|
NAME | DESCRIPTION | SUDOERS FILE FORMAT | SUDOERS OPTIONS | GROUP PROVIDER PLUGINS | LOG FORMAT | I/O LOG FILES | FILES | EXAMPLES | SECURITY NOTES | DEBUGGING | SEE ALSO | AUTHORS | CAVEATS | BUGS | SUPPORT | DISCLAIMER | COLOPHON |
|
|
|
SUDOERS(5) BSD File Formats Manual SUDOERS(5)
sudoers — default sudo security policy plugin
The sudoers policy plugin determines a user's sudo privileges. It
is the default sudo policy plugin. The policy is driven by the
/etc/sudoers file or, optionally in LDAP. The policy format is
described in detail in the SUDOERS FILE FORMAT section. For
information on storing sudoers policy information in LDAP, please
see sudoers.ldap(5).
Configuring sudo.conf for sudoers
sudo consults the sudo.conf(5) file to determine which policy and
I/O logging plugins to load. If no sudo.conf(5) file is present,
or if it contains no Plugin lines, sudoers will be used for policy
decisions and I/O logging. To explicitly configure sudo.conf(5) to
use the sudoers plugin, the following configuration can be used.
Plugin sudoers_audit sudoers.so
Plugin sudoers_policy sudoers.so
Plugin sudoers_io sudoers.so
Starting with sudo 1.8.5, it is possible to specify optional
arguments to the sudoers plugin in the sudo.conf(5) file. Plugin
arguments, if any, should be listed after the path to the plugin
(i.e., after sudoers.so). The arguments are only effective for the
plugin that opens (and parses) the sudoers file.
For sudo version 1.9.1 and higher, this is the sudoers_audit
plugin. For older versions, it is the sudoers_policy plugin.
Multiple arguments may be specified, separated by white space. For
example:
Plugin sudoers_audit sudoers.so sudoers_mode=0400 error_recovery=false
The following plugin arguments are supported:
error_recovery=bool
The error_recovery argument can be used to control
whether sudoers should attempt to recover from syntax
errors in the sudoers file. If set to true (the
default), sudoers will try to recover from a syntax error
by discarding the portion of the line that contains the
error until the end of the line. A value of false will
disable error recovery. Prior to version 1.9.3, no error
recovery was performed.
ldap_conf=pathname
The ldap_conf argument can be used to override the
default path to the ldap.conf file.
ldap_secret=pathname
The ldap_secret argument can be used to override the
default path to the ldap.secret file.
sudoers_file=pathname
The sudoers_file argument can be used to override the
default path to the sudoers file.
sudoers_uid=uid
The sudoers_uid argument can be used to override the
default owner of the sudoers file. It should be
specified as a numeric user-ID.
sudoers_gid=gid
The sudoers_gid argument can be used to override the
default group of the sudoers file. It must be specified
as a numeric group-ID (not a group name).
sudoers_mode=mode
The sudoers_mode argument can be used to override the
default file mode for the sudoers file. It should be
specified as an octal value.
For more information on configuring sudo.conf(5), please refer to
its manual.
User Authentication
The sudoers security policy requires that most users authenticate
themselves before they can use sudo. A password is not required if
the invoking user is root, if the target user is the same as the
invoking user, or if the policy has disabled authentication for the
user or command. Unlike su(1), when sudoers requires
authentication, it validates the invoking user's credentials, not
the target user's (or root's) credentials. This can be changed via
the rootpw, targetpw and runaspw flags, described later.
If a user who is not listed in the policy tries to run a command
via sudo, mail is sent to the proper authorities. The address used
for such mail is configurable via the mailto Defaults entry
(described later) and defaults to root.
Note that no mail will be sent if an unauthorized user tries to run
sudo with the -l or -v option unless there is an authentication
error and either the mail_always or mail_badpass flags are enabled.
This allows users to determine for themselves whether or not they
are allowed to use sudo. By default, all attempts to run sudo
(successful or not) are logged, regardless of whether or not mail
is sent.
If sudo is run by root and the SUDO_USER environment variable is
set, the sudoers policy will use this value to determine who the
actual user is. This can be used by a user to log commands through
sudo even when a root shell has been invoked. It also allows the
-e option to remain useful even when invoked via a sudo-run script
or program. Note, however, that the sudoers file lookup is still
done for root, not the user specified by SUDO_USER.
sudoers uses per-user time stamp files for credential caching.
Once a user has been authenticated, a record is written containing
the user-ID that was used to authenticate, the terminal session ID,
the start time of the session leader (or parent process) and a time
stamp (using a monotonic clock if one is available). The user may
then use sudo without a password for a short period of time (5
minutes unless overridden by the timestamp_timeout option). By
default, sudoers uses a separate record for each terminal, which
means that a user's login sessions are authenticated separately.
The timestamp_type option can be used to select the type of time
stamp record sudoers will use.
Logging
By default, sudoers logs both successful and unsuccessful attempts
(as well as errors). The log_allowed and log_denied flags can be
used to control this behavior. Messages can be logged to
syslog(3), a log file, or both. The default is to log to syslog(3)
but this is configurable via the syslog and logfile settings. See
LOG FORMAT for a description of the log file format.
sudoers is also capable of running a command in a pseudo-terminal
and logging all input and/or output. The standard input, standard
output and standard error can be logged even when not associated
with a terminal. I/O logging is not on by default but can be
enabled using the log_input and log_output options as well as the
LOG_INPUT and LOG_OUTPUT command tags. See I/O LOG FILES for
details on how I/O log files are stored.
Starting with version 1.9, the log_servers setting may be used to
send event and I/O log data to a remote server running sudo_logsrvd
or another service that implements the protocol described by
sudo_logsrv.proto(5).
Command environment
Since environment variables can influence program behavior, sudoers
provides a means to restrict which variables from the user's
environment are inherited by the command to be run. There are two
distinct ways sudoers can deal with environment variables.
By default, the env_reset flag is enabled. This causes commands to
be executed with a new, minimal environment. On AIX (and Linux
systems without PAM), the environment is initialized with the
contents of the /etc/environment file. The HOME, MAIL, SHELL,
LOGNAME and USER environment variables are initialized based on the
target user and the SUDO_* variables are set based on the invoking
user. Additional variables, such as DISPLAY, PATH and TERM, are
preserved from the invoking user's environment if permitted by the
env_check or env_keep options. A few environment variables are
treated specially. If the PATH and TERM variables are not
preserved from the user's environment, they will be set to default
values. The LOGNAME and USER are handled as a single entity. If
one of them is preserved (or removed) from the user's environment,
the other will be as well. If LOGNAME and USER are to be preserved
but only one of them is present in the user's environment, the
other will be set to the same value. This avoids an inconsistent
environment where one of the variables describing the user name is
set to the invoking user and one is set to the target user.
Environment variables with a value beginning with () are removed
unless both the name and value parts are matched by env_keep or
env_check, as they may be interpreted as functions by the bash
shell. Prior to version 1.8.11, such variables were always
removed.
If, however, the env_reset flag is disabled, any variables not
explicitly denied by the env_check and env_delete options are
allowed and their values are inherited from the invoking process.
Prior to version 1.8.21, environment variables with a value
beginning with () were always removed. Beginning with version
1.8.21, a pattern in env_delete is used to match bash shell
functions instead. Since it is not possible to block all
potentially dangerous environment variables, use of the default
env_reset behavior is encouraged.
Environment variables specified by env_check, env_delete, or
env_keep may include one or more ‘*’ characters which will match
zero or more characters. No other wildcard characters are
supported.
By default, environment variables are matched by name. However, if
the pattern includes an equal sign (‘=’), both the variables name
and value must match. For example, a bash shell function could be
matched as follows:
env_keep += "BASH_FUNC_my_func%%=()*"
Without the “=()*” suffix, this would not match, as bash shell
functions are not preserved by default.
The complete list of environment variables that are preserved or
removed, as modified by global Defaults parameters in sudoers, is
displayed when sudo is run by root with the -V option. Please note
that the list of environment variables to remove varies based on
the operating system sudo is running on.
Other sudoers options may influence the command environment, such
as always_set_home, secure_path, set_logname, and set_home.
On systems that support PAM where the pam_env module is enabled for
sudo, variables in the PAM environment may be merged in to the
environment. If a variable in the PAM environment is already
present in the user's environment, the value will only be
overridden if the variable was not preserved by sudoers. When
env_reset is enabled, variables preserved from the invoking user's
environment by the env_keep list take precedence over those in the
PAM environment. When env_reset is disabled, variables present the
invoking user's environment take precedence over those in the PAM
environment unless they match a pattern in the env_delete list.
Note that the dynamic linker on most operating systems will remove
variables that can control dynamic linking from the environment of
set-user-ID executables, including sudo. Depending on the
operating system this may include _RLD*, DYLD_*, LD_*, LDR_*,
LIBPATH, SHLIB_PATH, and others. These type of variables are
removed from the environment before sudo even begins execution and,
as such, it is not possible for sudo to preserve them.
As a special case, if the -i option (initial login) is specified,
sudoers will initialize the environment regardless of the value of
env_reset. The DISPLAY, PATH and TERM variables remain unchanged;
HOME, MAIL, SHELL, USER, and LOGNAME are set based on the target
user. On AIX (and Linux systems without PAM), the contents of
/etc/environment are also included. All other environment
variables are removed unless permitted by env_keep or env_check,
described above.
Finally, the restricted_env_file and env_file files are applied, if
present. The variables in restricted_env_file are applied first
and are subject to the same restrictions as the invoking user's
environment, as detailed above. The variables in env_file are
applied last and are not subject to these restrictions. In both
cases, variables present in the files will only be set to their
specified values if they would not conflict with an existing
environment variable.
The sudoers file is composed of two types of entries: aliases
(basically variables) and user specifications (which specify who
may run what).
When multiple entries match for a user, they are applied in order.
Where there are multiple matches, the last match is used (which is
not necessarily the most specific match).
The sudoers file grammar will be described below in Extended
Backus-Naur Form (EBNF). Don't despair if you are unfamiliar with
EBNF; it is fairly simple, and the definitions below are annotated.
Quick guide to EBNF
EBNF is a concise and exact way of describing the grammar of a
language. Each EBNF definition is made up of production rules.
E.g.,
symbol ::= definition | alternate1 | alternate2 ...
Each production rule references others and thus makes up a grammar
for the language. EBNF also contains the following operators,
which many readers will recognize from regular expressions. Do
not, however, confuse them with “wildcard” characters, which have
different meanings.
? Means that the preceding symbol (or group of symbols) is
optional. That is, it may appear once or not at all.
* Means that the preceding symbol (or group of symbols) may
appear zero or more times.
+ Means that the preceding symbol (or group of symbols) may
appear one or more times.
Parentheses may be used to group symbols together. For clarity, we
will use single quotes ('') to designate what is a verbatim
character string (as opposed to a symbol name).
Aliases
There are four kinds of aliases: User_Alias, Runas_Alias,
Host_Alias and Cmnd_Alias. Beginning with sudo 1.9.0, Cmd_Alias
may be used in place of Cmnd_Alias if desired.
Alias ::= 'User_Alias' User_Alias_Spec (':' User_Alias_Spec)* |
'Runas_Alias' Runas_Alias_Spec (':' Runas_Alias_Spec)* |
'Host_Alias' Host_Alias_Spec (':' Host_Alias_Spec)* |
'Cmnd_Alias' Cmnd_Alias_Spec (':' Cmnd_Alias_Spec)* |
'Cmd_Alias' Cmnd_Alias_Spec (':' Cmnd_Alias_Spec)*
User_Alias ::= NAME
User_Alias_Spec ::= User_Alias '=' User_List
Runas_Alias ::= NAME
Runas_Alias_Spec ::= Runas_Alias '=' Runas_List
Host_Alias ::= NAME
Host_Alias_Spec ::= Host_Alias '=' Host_List
Cmnd_Alias ::= NAME
Cmnd_Alias_Spec ::= Cmnd_Alias '=' Cmnd_List
NAME ::= [A-Z]([A-Z][0-9]_)*
Each alias definition is of the form
Alias_Type NAME = item1, item2, ...
where Alias_Type is one of User_Alias, Runas_Alias, Host_Alias, or
Cmnd_Alias. A NAME is a string of uppercase letters, numbers, and
underscore characters (‘_’). A NAME must start with an uppercase
letter. It is possible to put several alias definitions of the
same type on a single line, joined by a colon (‘:’). E.g.,
Alias_Type NAME = item1, item2, item3 : NAME = item4, item5
It is a syntax error to redefine an existing alias. It is possible
to use the same name for aliases of different types, but this is
not recommended.
The definitions of what constitutes a valid alias member follow.
User_List ::= User |
User ',' User_List
User ::= '!'* user name |
'!'* #uid |
'!'* %group |
'!'* %#gid |
'!'* +netgroup |
'!'* %:nonunix_group |
'!'* %:#nonunix_gid |
'!'* User_Alias
A User_List is made up of one or more user names, user-IDs
(prefixed with ‘#’), system group names and IDs (prefixed with ‘%’
and ‘%#’ respectively), netgroups (prefixed with ‘+’), non-Unix
group names and IDs (prefixed with ‘%:’ and ‘%:#’ respectively) and
User_Aliases. Each list item may be prefixed with zero or more ‘!’
operators. An odd number of ‘!’ operators negate the value of the
item; an even number just cancel each other out. User netgroups
are matched using the user and domain members only; the host member
is not used when matching.
A user name, uid, group, gid, netgroup, nonunix_group or
nonunix_gid may be enclosed in double quotes to avoid the need for
escaping special characters. Alternately, special characters may
be specified in escaped hex mode, e.g., \x20 for space. When using
double quotes, any prefix characters must be included inside the
quotes.
The actual nonunix_group and nonunix_gid syntax depends on the
underlying group provider plugin. For instance, the QAS AD plugin
supports the following formats:
• Group in the same domain: "%:Group Name"
• Group in any domain: "%:Group Name@FULLY.QUALIFIED.DOMAIN"
• Group SID: "%:S-1-2-34-5678901234-5678901234-5678901234-567"
See GROUP PROVIDER PLUGINS for more information.
Note that quotes around group names are optional. Unquoted strings
must use a backslash (‘\’) to escape spaces and special characters.
See Other special characters and reserved words for a list of
characters that need to be escaped.
Runas_List ::= Runas_Member |
Runas_Member ',' Runas_List
Runas_Member ::= '!'* user name |
'!'* #uid |
'!'* %group |
'!'* %#gid |
'!'* %:nonunix_group |
'!'* %:#nonunix_gid |
'!'* +netgroup |
'!'* Runas_Alias
A Runas_List is similar to a User_List except that instead of
User_Aliases it can contain Runas_Aliases. Note that user names
and groups are matched as strings. In other words, two users
(groups) with the same user (group) ID are considered to be
distinct. If you wish to match all user names with the same user-
ID (e.g., root and toor), you can use a user-ID instead of a name
(#0 in the example given). Note that the user-ID or group-ID
specified in a Runas_Member need not be listed in the password or
group database.
Host_List ::= Host |
Host ',' Host_List
Host ::= '!'* host name |
'!'* ip_addr |
'!'* network(/netmask)? |
'!'* +netgroup |
'!'* Host_Alias
A Host_List is made up of one or more host names, IP addresses,
network numbers, netgroups (prefixed with ‘+’) and other aliases.
Again, the value of an item may be negated with the ‘!’ operator.
Host netgroups are matched using the host (both qualified and
unqualified) and domain members only; the user member is not used
when matching. If you specify a network number without a netmask,
sudo will query each of the local host's network interfaces and, if
the network number corresponds to one of the hosts's network
interfaces, will use the netmask of that interface. The netmask
may be specified either in standard IP address notation (e.g.,
255.255.255.0 or ffff:ffff:ffff:ffff::), or CIDR notation (number
of bits, e.g., 24 or 64). A host name may include shell-style
wildcards (see the Wildcards section below), but unless the host
name command on your machine returns the fully qualified host name,
you'll need to use the fqdn flag for wildcards to be useful. Note
that sudo only inspects actual network interfaces; this means that
IP address 127.0.0.1 (localhost) will never match. Also, the host
name “localhost” will only match if that is the actual host name,
which is usually only the case for non-networked systems.
digest ::= [A-Fa-f0-9]+ |
[A-Za-z0-9\+/=]+
Digest_Spec ::= "sha224" ':' digest |
"sha256" ':' digest |
"sha384" ':' digest |
"sha512" ':' digest
Digest_List ::= Digest_Spec |
Digest_Spec ',' Digest_List
Cmnd_List ::= Cmnd |
Cmnd ',' Cmnd_List
command name ::= file name |
file name args |
file name '""'
Edit_Spec ::= "sudoedit" file name+
Cmnd ::= Digest_List? '!'* command name |
'!'* directory |
'!'* Edit_Spec |
'!'* Cmnd_Alias
A Cmnd_List is a list of one or more command names, directories,
and other aliases. A command name is a fully qualified file name
which may include shell-style wildcards (see the Wildcards section
below). A simple file name allows the user to run the command with
any arguments they wish. However, you may also specify command
line arguments (including wildcards). Alternately, you can specify
"" to indicate that the command may only be run without command
line arguments. A directory is a fully qualified path name ending
in a ‘/’. When you specify a directory in a Cmnd_List, the user
will be able to run any file within that directory (but not in any
sub-directories therein).
If a Cmnd has associated command line arguments, then the arguments
in the Cmnd must match exactly those given by the user on the
command line (or match the wildcards if there are any). Note that
the following characters must be escaped with a ‘\’ if they are
used in command arguments: ‘,’, ‘:’, ‘=’, ‘\’. The built-in
command “sudoedit” is used to permit a user to run sudo with the -e
option (or as sudoedit). It may take command line arguments just
as a normal command does. Note that “sudoedit” is a command built
into sudo itself and must be specified in the sudoers file without
a leading path. If a leading path is present, for example
/usr/bin/sudoedit, the path name will be silently converted to
“sudoedit”. A fully-qualified path for sudoedit is treated as an
error by visudo.
A command name may be preceded by a Digest_List, a comma-separated
list of one or more Digest_Spec entries. If a Digest_List is
present, the command will only match successfully if it can be
verified using one of the SHA-2 digests in the list. Starting with
version 1.9.0, the ALL reserved word can be used in conjunction
with a Digest_List. The following digest formats are supported:
sha224, sha256, sha384 and sha512. The string may be specified in
either hex or base64 format (base64 is more compact). There are
several utilities capable of generating SHA-2 digests in hex format
such as openssl, shasum, sha224sum, sha256sum, sha384sum,
sha512sum.
For example, using openssl:
$ openssl dgst -sha224 /bin/ls
SHA224(/bin/ls)= 118187da8364d490b4a7debbf483004e8f3e053ec954309de2c41a25
It is also possible to use openssl to generate base64 output:
$ openssl dgst -binary -sha224 /bin/ls | openssl base64
EYGH2oNk1JC0p9679IMATo8+BT7JVDCd4sQaJQ==
Warning, if the user has write access to the command itself
(directly or via a sudo command), it may be possible for the user
to replace the command after the digest check has been performed
but before the command is executed. A similar race condition
exists on systems that lack the fexecve(2) system call when the
directory in which the command is located is writable by the user.
See the description of the fdexec setting for more information on
how sudo executes commands that have an associated digest.
Command digests are only supported by version 1.8.7 or higher.
Defaults
Certain configuration options may be changed from their default
values at run-time via one or more Default_Entry lines. These may
affect all users on any host, all users on a specific host, a
specific user, a specific command, or commands being run as a
specific user. Note that per-command entries may not include
command line arguments. If you need to specify arguments, define a
Cmnd_Alias and reference that instead.
Default_Type ::= 'Defaults' |
'Defaults' '@' Host_List |
'Defaults' ':' User_List |
'Defaults' '!' Cmnd_List |
'Defaults' '>' Runas_List
Default_Entry ::= Default_Type Parameter_List
Parameter_List ::= Parameter |
Parameter ',' Parameter_List
Parameter ::= Parameter '=' Value |
Parameter '+=' Value |
Parameter '-=' Value |
'!'* Parameter
Parameters may be flags, integer values, strings, or lists. Flags
are implicitly boolean and can be turned off via the ‘!’ operator.
Some integer, string and list parameters may also be used in a
boolean context to disable them. Values may be enclosed in double
quotes ("") when they contain multiple words. Special characters
may be escaped with a backslash (‘\’).
Lists have two additional assignment operators, += and -=. These
operators are used to add to and delete from a list respectively.
It is not an error to use the -= operator to remove an element that
does not exist in a list.
Defaults entries are parsed in the following order: generic, host,
user and runas Defaults first, then command defaults. If there are
multiple Defaults settings of the same type, the last matching
setting is used. The following Defaults settings are parsed before
all others since they may affect subsequent entries: fqdn,
group_plugin, runas_default, sudoers_locale.
See SUDOERS OPTIONS for a list of supported Defaults parameters.
User specification
User_Spec ::= User_List Host_List '=' Cmnd_Spec_List \
(':' Host_List '=' Cmnd_Spec_List)*
Cmnd_Spec_List ::= Cmnd_Spec |
Cmnd_Spec ',' Cmnd_Spec_List
Cmnd_Spec ::= Runas_Spec? Option_Spec* Tag_Spec* Cmnd
Runas_Spec ::= '(' Runas_List? (':' Runas_List)? ')'
Option_Spec ::= (Date_Spec | Timeout_Spec | Chdir_Spec | Chroot_Spec)
Date_Spec ::= ('NOTBEFORE=timestamp' | 'NOTAFTER=timestamp')
Timeout_Spec ::= 'TIMEOUT=timeout'
Chdir_Spec ::= 'CWD=directory'
Chroot_Spec ::= 'CHROOT=directory'
Tag_Spec ::= ('EXEC:' | 'NOEXEC:' | 'FOLLOW:' | 'NOFOLLOW' |
'LOG_INPUT:' | 'NOLOG_INPUT:' | 'LOG_OUTPUT:' |
'NOLOG_OUTPUT:' | 'MAIL:' | 'NOMAIL:' | 'PASSWD:' |
'NOPASSWD:' | 'SETENV:' | 'NOSETENV:')
A user specification determines which commands a user may run (and
as what user) on specified hosts. By default, commands are run as
root, but this can be changed on a per-command basis.
The basic structure of a user specification is “who where =
(as_whom) what”. Let's break that down into its constituent parts:
Runas_Spec
A Runas_Spec determines the user and/or the group that a command
may be run as. A fully-specified Runas_Spec consists of two
Runas_Lists (as defined above) separated by a colon (‘:’) and
enclosed in a set of parentheses. The first Runas_List indicates
which users the command may be run as via the -u option. The
second defines a list of groups that can be specified via the -g
option in addition to any of the target user's groups. If both
Runas_Lists are specified, the command may be run with any
combination of users and groups listed in their respective
Runas_Lists. If only the first is specified, the command may be run
as any user in the list but no -g option may be specified. If the
first Runas_List is empty but the second is specified, the command
may be run as the invoking user with the group set to any listed in
the Runas_List. If both Runas_Lists are empty, the command may
only be run as the invoking user. If no Runas_Spec is specified
the command may be run as root and no group may be specified.
A Runas_Spec sets the default for the commands that follow it.
What this means is that for the entry:
dgb boulder = (operator) /bin/ls, /bin/kill, /usr/bin/lprm
The user dgb may run /bin/ls, /bin/kill, and /usr/bin/lprm on the
host boulder—but only as operator. E.g.,
$ sudo -u operator /bin/ls
It is also possible to override a Runas_Spec later on in an entry.
If we modify the entry like so:
dgb boulder = (operator) /bin/ls, (root) /bin/kill, /usr/bin/lprm
Then user dgb is now allowed to run /bin/ls as operator, but
/bin/kill and /usr/bin/lprm as root.
We can extend this to allow dgb to run /bin/ls with either the user
or group set to operator:
dgb boulder = (operator : operator) /bin/ls, (root) /bin/kill,\
/usr/bin/lprm
Note that while the group portion of the Runas_Spec permits the
user to run as command with that group, it does not force the user
to do so. If no group is specified on the command line, the
command will run with the group listed in the target user's
password database entry. The following would all be permitted by
the sudoers entry above:
$ sudo -u operator /bin/ls
$ sudo -u operator -g operator /bin/ls
$ sudo -g operator /bin/ls
In the following example, user tcm may run commands that access a
modem device file with the dialer group.
tcm boulder = (:dialer) /usr/bin/tip, /usr/bin/cu,\
/usr/local/bin/minicom
Note that in this example only the group will be set, the command
still runs as user tcm. E.g.
$ sudo -g dialer /usr/bin/cu
Multiple users and groups may be present in a Runas_Spec, in which
case the user may select any combination of users and groups via
the -u and -g options. In this example:
alan ALL = (root, bin : operator, system) ALL
user alan may run any command as either user root or bin,
optionally setting the group to operator or system.
Option_Spec
A Cmnd may have zero or more options associated with it. Options
may consist of start and/or end dates and command timeouts. Once
an option is set for a Cmnd, subsequent Cmnds in the
Cmnd_Spec_List, inherit that option unless it is overridden by
another option. Note that the option names are reserved words in
sudoers. This means that none of the valid option names (see
below) can be used when declaring an alias.
Date_Spec
sudoers rules can be specified with a start and end date via the
NOTBEFORE and NOTAFTER settings. The time stamp must be specified
in Generalized Time as defined by RFC 4517. The format is
effectively yyyymmddHHMMSSZ where the minutes and seconds are
optional. The ‘Z’ suffix indicates that the time stamp is in
Coordinated Universal Time (UTC). It is also possible to specify a
timezone offset from UTC in hours and minutes instead of a ‘Z’.
For example, ‘-0500’ would correspond to Eastern Standard time in
the US. As an extension, if no ‘Z’ or timezone offset is
specified, local time will be used.
The following are all valid time stamps:
20170214083000Z
2017021408Z
20160315220000-0500
20151201235900
Timeout_Spec
A command may have a timeout associated with it. If the timeout
expires before the command has exited, the command will be
terminated. The timeout may be specified in combinations of days,
hours, minutes and seconds with a single-letter case-insensitive
suffix that indicates the unit of time. For example, a timeout of
7 days, 8 hours, 30 minutes and 10 seconds would be written as
7d8h30m10s. If a number is specified without a unit, seconds are
assumed. Any of the days, minutes, hours or seconds may be
omitted. The order must be from largest to smallest unit and a
unit may not be specified more than once.
The following are all valid timeout values: 7d8h30m10s, 14d, 8h30m,
600s, 3600. The following are invalid timeout values: 12m2w1d,
30s10m4h, 1d2d3h.
This setting is only supported by version 1.8.20 or higher.
Chdir_Spec
The working directory that the command will be run in can be
specified using the CWD setting. The directory must be a fully-
qualified path name beginning with a ‘/’ or ‘~’ character, or the
special value “*”. A value of “*” indicates that the user may
specify the working directory by running sudo with the -D option.
By default, commands are run from the invoking user's current
working directory, unless the -i option is given. Path names of
the form ~user/path/name are interpreted as being relative to the
named user's home directory. If the user name is omitted, the path
will be relative to the runas user's home directory.
This setting is only supported by version 1.9.3 or higher.
Chroot_Spec
The root directory that the command will be run in can be specified
using the CHROOT setting. The directory must be a fully-qualified
path name beginning with a ‘/’ or ‘~’ character, or the special
value “*”. A value of “*” indicates that the user may specify the
root directory by running sudo with the -R option. This setting
can be used to run the command in a chroot(2) “sandbox” similar to
the chroot(8) utility. Path names of the form ~user/path/name are
interpreted as being relative to the named user's home directory.
If the user name is omitted, the path will be relative to the runas
user's home directory.
This setting is only supported by version 1.9.3 or higher.
Tag_Spec
A command may have zero or more tags associated with it. The
following tag values are supported: EXEC, NOEXEC, FOLLOW, NOFOLLOW,
LOG_INPUT, NOLOG_INPUT, LOG_OUTPUT, NOLOG_OUTPUT, MAIL, NOMAIL,
PASSWD, NOPASSWD, SETENV, and NOSETENV. Once a tag is set on a
Cmnd, subsequent Cmnds in the Cmnd_Spec_List, inherit the tag
unless it is overridden by the opposite tag (in other words, PASSWD
overrides NOPASSWD and NOEXEC overrides EXEC).
EXEC and NOEXEC
If sudo has been compiled with noexec support and the underlying
operating system supports it, the NOEXEC tag can be used to
prevent a dynamically-linked executable from running further
commands itself.
In the following example, user aaron may run /usr/bin/more and
/usr/bin/vi but shell escapes will be disabled.
aaron shanty = NOEXEC: /usr/bin/more, /usr/bin/vi
See the Preventing shell escapes section below for more details
on how NOEXEC works and whether or not it will work on your
system.
FOLLOW and NOFOLLOW Starting with version 1.8.15, sudoedit will not
open a file that is a symbolic link unless the sudoedit_follow
flag is enabled. The FOLLOW and NOFOLLOW tags override the value
of sudoedit_follow and can be used to permit (or deny) the
editing of symbolic links on a per-command basis. These tags are
only effective for the sudoedit command and are ignored for all
other commands.
LOG_INPUT and NOLOG_INPUT
These tags override the value of the log_input flag on a per-
command basis. For more information, see the description of
log_input in the SUDOERS OPTIONS section below.
LOG_OUTPUT and NOLOG_OUTPUT
These tags override the value of the log_output flag on a per-
command basis. For more information, see the description of
log_output in the SUDOERS OPTIONS section below.
MAIL and NOMAIL
These tags provide fine-grained control over whether mail will be
sent when a user runs a command by overriding the value of the
mail_all_cmnds flag on a per-command basis. They have no effect
when sudo is run with the -l or -v options. A NOMAIL tag will
also override the mail_always and mail_no_perms options. For
more information, see the descriptions of mail_all_cmnds,
mail_always, and mail_no_perms in the SUDOERS OPTIONS section
below.
PASSWD and NOPASSWD
By default, sudo requires that a user authenticate him or herself
before running a command. This behavior can be modified via the
NOPASSWD tag. Like a Runas_Spec, the NOPASSWD tag sets a default
for the commands that follow it in the Cmnd_Spec_List.
Conversely, the PASSWD tag can be used to reverse things. For
example:
ray rushmore = NOPASSWD: /bin/kill, /bin/ls, /usr/bin/lprm
would allow the user ray to run /bin/kill, /bin/ls, and
/usr/bin/lprm as root on the machine rushmore without
authenticating himself. If we only want ray to be able to run
/bin/kill without a password the entry would be:
ray rushmore = NOPASSWD: /bin/kill, PASSWD: /bin/ls, /usr/bin/lprm
Note, however, that the PASSWD tag has no effect on users who are
in the group specified by the exempt_group setting.
By default, if the NOPASSWD tag is applied to any of a user's
entries for the current host, the user will be able to run “sudo
-l” without a password. Additionally, a user may only run “sudo
-v” without a password if all of the user's entries for the
current host have the NOPASSWD tag. This behavior may be
overridden via the verifypw and listpw options.
SETENV and NOSETENV
These tags override the value of the setenv flag on a per-command
basis. Note that if SETENV has been set for a command, the user
may disable the env_reset flag from the command line via the -E
option. Additionally, environment variables set on the command
line are not subject to the restrictions imposed by env_check,
env_delete, or env_keep. As such, only trusted users should be
allowed to set variables in this manner. If the command matched
is ALL, the SETENV tag is implied for that command; this default
may be overridden by use of the NOSETENV tag.
Wildcards
sudo allows shell-style wildcards (aka meta or glob characters) to
be used in host names, path names and command line arguments in the
sudoers file. Wildcard matching is done via the glob(3) and
fnmatch(3) functions as specified by IEEE Std 1003.1 (“POSIX.1”).
* Matches any set of zero or more characters (including
white space).
? Matches any single character (including white space).
[...] Matches any character in the specified range.
[!...] Matches any character not in the specified range.
\x For any character ‘x’, evaluates to ‘x’. This is used to
escape special characters such as: ‘*’, ‘?’, ‘[’, and
‘]’.
Note that these are not regular expressions. Unlike a regular
expression there is no way to match one or more characters within a
range.
Character classes may be used if your system's glob(3) and
fnmatch(3) functions support them. However, because the ‘:’
character has special meaning in sudoers, it must be escaped. For
example:
/bin/ls [[\:alpha\:]]*
Would match any file name beginning with a letter.
Note that a forward slash (‘/’) will not be matched by wildcards
used in the file name portion of the command. This is to make a
path like:
/usr/bin/*
match /usr/bin/who but not /usr/bin/X11/xterm.
When matching the command line arguments, however, a slash does get
matched by wildcards since command line arguments may contain
arbitrary strings and not just path names.
Wildcards in command line arguments should be used with care.
Command line arguments are matched as a single, concatenated
string. This mean a wildcard character such as ‘?’ or ‘*’ will
match across word boundaries, which may be unexpected. For
example, while a sudoers entry like:
%operator ALL = /bin/cat /var/log/messages*
will allow command like:
$ sudo cat /var/log/messages.1
It will also allow:
$ sudo cat /var/log/messages /etc/shadow
which is probably not what was intended. In most cases it is
better to do command line processing outside of the sudoers file in
a scripting language.
Exceptions to wildcard rules
The following exceptions apply to the above rules:
"" If the empty string "" is the only command line argument
in the sudoers file entry it means that command is not
allowed to be run with any arguments.
sudoedit Command line arguments to the sudoedit built-in command
should always be path names, so a forward slash (‘/’)
will not be matched by a wildcard.
Including other files from within sudoers
It is possible to include other sudoers files from within the
sudoers file currently being parsed using the @include and
@includedir directives. For compatibility with sudo versions prior
to 1.9.1, #include and #includedir are also accepted.
An include file can be used, for example, to keep a site-wide
sudoers file in addition to a local, per-machine file. For the
sake of this example the site-wide sudoers file will be
/etc/sudoers and the per-machine one will be /etc/sudoers.local.
To include /etc/sudoers.local from within /etc/sudoers one would
use the following line in /etc/sudoers:
@include /etc/sudoers.local
When sudo reaches this line it will suspend processing of the
current file (/etc/sudoers) and switch to /etc/sudoers.local. Upon
reaching the end of /etc/sudoers.local, the rest of /etc/sudoers
will be processed. Files that are included may themselves include
other files. A hard limit of 128 nested include files is enforced
to prevent include file loops.
The path to the include file may contain white space if it is
escaped with a backslash (‘\’). Alternately, the entire path may
be enclosed in double quotes (""), in which case no escaping is
necessary. To include a literal backslash in the path, ‘\\’ should
be used.
If the path to the include file is not fully-qualified (does not
begin with a ‘/’), it must be located in the same directory as the
sudoers file it was included from. For example, if /etc/sudoers
contains the line:
@include sudoers.local
the file that will be included is /etc/sudoers.local.
The file name may also include the %h escape, signifying the short
form of the host name. In other words, if the machine's host name
is “xerxes”, then
@include /etc/sudoers.%h
will cause sudo to include the file /etc/sudoers.xerxes.
The @includedir directive can be used to create a sudoers.d
directory that the system package manager can drop sudoers file
rules into as part of package installation. For example, given:
@includedir /etc/sudoers.d
sudo will suspend processing of the current file and read each file
in /etc/sudoers.d, skipping file names that end in ‘~’ or contain a
‘.’ character to avoid causing problems with package manager or
editor temporary/backup files. Files are parsed in sorted lexical
order. That is, /etc/sudoers.d/01_first will be parsed before
/etc/sudoers.d/10_second. Be aware that because the sorting is
lexical, not numeric, /etc/sudoers.d/1_whoops would be loaded after
/etc/sudoers.d/10_second. Using a consistent number of leading
zeroes in the file names can be used to avoid such problems. After
parsing the files in the directory, control returns to the file
that contained the @includedir directive.
Note that unlike files included via @include, visudo will not edit
the files in a @includedir directory unless one of them contains a
syntax error. It is still possible to run visudo with the -f flag
to edit the files directly, but this will not catch the
redefinition of an alias that is also present in a different file.
Other special characters and reserved words
The pound sign (‘#’) is used to indicate a comment (unless it is
part of a #include directive or unless it occurs in the context of
a user name and is followed by one or more digits, in which case it
is treated as a user-ID). Both the comment character and any text
after it, up to the end of the line, are ignored.
The reserved word ALL is a built-in alias that always causes a
match to succeed. It can be used wherever one might otherwise use
a Cmnd_Alias, User_Alias, Runas_Alias, or Host_Alias. Attempting
to define an alias named ALL will result in a syntax error. Please
note that using ALL can be dangerous since in a command context, it
allows the user to run any command on the system.
The following option names permitted in an Option_Spec are also
considered reserved words: CHROOT, TIMEOUT, CWD, NOTBEFORE and
NOTAFTER. Attempting to define an alias with the same name as one
of the options will result in a syntax error.
An exclamation point (‘!’) can be used as a logical not operator in
a list or alias as well as in front of a Cmnd. This allows one to
exclude certain values. For the ‘!’ operator to be effective,
there must be something for it to exclude. For example, to match
all users except for root one would use:
ALL,!root
If the ALL, is omitted, as in:
!root
it would explicitly deny root but not match any other users. This
is different from a true “negation” operator.
Note, however, that using a ‘!’ in conjunction with the built-in
ALL alias to allow a user to run “all but a few” commands rarely
works as intended (see SECURITY NOTES below).
Long lines can be continued with a backslash (‘\’) as the last
character on the line.
White space between elements in a list as well as special syntactic
characters in a User Specification (‘=’, ‘:’, ‘(’, ‘)’) is
optional.
The following characters must be escaped with a backslash (‘\’)
when used as part of a word (e.g., a user name or host name): ‘!’,
‘=’, ‘:’, ‘,’, ‘(’, ‘)’, ‘\’.
sudo's behavior can be modified by Default_Entry lines, as
explained earlier. A list of all supported Defaults parameters,
grouped by type, are listed below.
Boolean Flags:
always_query_group_plugin
If a group_plugin is configured, use it to
resolve groups of the form %group as long as
there is not also a system group of the same
name. Normally, only groups of the form %:group
are passed to the group_plugin. This flag is off
by default.
always_set_home If enabled, sudo will set the HOME environment
variable to the home directory of the target user
(which is the root user unless the -u option is
used). This flag is largely obsolete and has no
effect unless the env_reset flag has been
disabled or HOME is present in the env_keep list,
both of which are strongly discouraged. This
flag is off by default.
authenticate If set, users must authenticate themselves via a
password (or other means of authentication)
before they may run commands. This default may
be overridden via the PASSWD and NOPASSWD tags.
This flag is on by default.
case_insensitive_group
If enabled, group names in sudoers will be
matched in a case insensitive manner. This may
be necessary when users are stored in LDAP or AD.
This flag is on by default.
case_insensitive_user
If enabled, user names in sudoers will be matched
in a case insensitive manner. This may be
necessary when groups are stored in LDAP or AD.
This flag is on by default.
closefrom_override
If set, the user may use the -C option which
overrides the default starting point at which
sudo begins closing open file descriptors. This
flag is off by default.
compress_io If set, and sudo is configured to log a command's
input or output, the I/O logs will be compressed
using zlib. This flag is on by default when sudo
is compiled with zlib support.
exec_background By default, sudo runs a command as the foreground
process as long as sudo itself is running in the
foreground. When the exec_background flag is
enabled and the command is being run in a pseudo-
terminal (due to I/O logging or the use_pty
flag), the command will be run as a background
process. Attempts to read from the controlling
terminal (or to change terminal settings) will
result in the command being suspended with the
SIGTTIN signal (or SIGTTOU in the case of
terminal settings). If this happens when sudo is
a foreground process, the command will be granted
the controlling terminal and resumed in the
foreground with no user intervention required.
The advantage of initially running the command in
the background is that sudo need not read from
the terminal unless the command explicitly
requests it. Otherwise, any terminal input must
be passed to the command, whether it has required
it or not (the kernel buffers terminals so it is
not possible to tell whether the command really
wants the input). This is different from
historic sudo behavior or when the command is not
being run in a pseudo-terminal.
For this to work seamlessly, the operating system
must support the automatic restarting of system
calls. Unfortunately, not all operating systems
do this by default, and even those that do may
have bugs. For example, macOS fails to restart
the tcgetattr() and tcsetattr() system calls
(this is a bug in macOS). Furthermore, because
this behavior depends on the command stopping
with the SIGTTIN or SIGTTOU signals, programs
that catch these signals and suspend themselves
with a different signal (usually SIGTOP) will not
be automatically foregrounded. Some versions of
the linux su(1) command behave this way. This
flag is off by default.
This setting is only supported by version 1.8.7
or higher. It has no effect unless I/O logging
is enabled or the use_pty flag is enabled.
env_editor If set, visudo will use the value of the
SUDO_EDITOR, VISUAL or EDITOR environment
variables before falling back on the default
editor list. Note that visudo is typically run
as root so this flag may allow a user with visudo
privileges to run arbitrary commands as root
without logging. An alternative is to place a
colon-separated list of “safe” editors int the
editor variable. visudo will then only use
SUDO_EDITOR, VISUAL or EDITOR if they match a
value specified in editor. If the env_reset flag
is enabled, the SUDO_EDITOR, VISUAL and/or EDITOR
environment variables must be present in the
env_keep list for the env_editor flag to function
when visudo is invoked via sudo. This flag is on
by default.
env_reset If set, sudo will run the command in a minimal
environment containing the TERM, PATH, HOME,
MAIL, SHELL, LOGNAME, USER and SUDO_* variables.
Any variables in the caller's environment or in
the file specified by the restricted_env_file
setting that match the env_keep and env_check
lists are then added, followed by any variables
present in the file specified by the env_file
setting (if any). The contents of the env_keep
and env_check lists, as modified by global
Defaults parameters in sudoers, are displayed
when sudo is run by root with the -V option. If
the secure_path setting is enabled, its value
will be used for the PATH environment variable.
This flag is on by default.
fast_glob Normally, sudo uses the glob(3) function to do
shell-style globbing when matching path names.
However, since it accesses the file system,
glob(3) can take a long time to complete for some
patterns, especially when the pattern references
a network file system that is mounted on demand
(auto mounted). The fast_glob flag causes sudo
to use the fnmatch(3) function, which does not
access the file system to do its matching. The
disadvantage of fast_glob is that it is unable to
match relative path names such as ./ls or
../bin/ls. This has security implications when
path names that include globbing characters are
used with the negation operator, ‘!’, as such
rules can be trivially bypassed. As such, this
flag should not be used when the sudoers file
contains rules that contain negated path names
which include globbing characters. This flag is
off by default.
fqdn Set this flag if you want to put fully qualified
host names in the sudoers file when the local
host name (as returned by the hostname command)
does not contain the domain name. In other
words, instead of myhost you would use
myhost.mydomain.edu. You may still use the short
form if you wish (and even mix the two). This
flag is only effective when the “canonical” host
name, as returned by the getaddrinfo() or
gethostbyname() function, is a fully-qualified
domain name. This is usually the case when the
system is configured to use DNS for host name
resolution.
If the system is configured to use the /etc/hosts
file in preference to DNS, the “canonical” host
name may not be fully-qualified. The order that
sources are queried for host name resolution is
usually specified in the /etc/nsswitch.conf,
/etc/netsvc.conf, /etc/host.conf, or, in some
cases, /etc/resolv.conf file. In the /etc/hosts
file, the first host name of the entry is
considered to be the “canonical” name; subsequent
names are aliases that are not used by sudoers.
For example, the following hosts file line for
the machine “xyzzy” has the fully-qualified
domain name as the “canonical” host name, and the
short version as an alias.
192.168.1.1 xyzzy.sudo.ws xyzzy
If the machine's hosts file entry is not
formatted properly, the fqdn flag will not be
effective if it is queried before DNS.
Beware that when using DNS for host name
resolution, turning on fqdn requires sudoers to
make DNS lookups which renders sudo unusable if
DNS stops working (for example if the machine is
disconnected from the network). Also note that
just like with the hosts file, you must use the
“canonical” name as DNS knows it. That is, you
may not use a host alias (CNAME entry) due to
performance issues and the fact that there is no
way to get all aliases from DNS.
This flag is off by default.
ignore_audit_errors
Allow commands to be run even if sudoers cannot
write to the audit log. If enabled, an audit log
write failure is not treated as a fatal error.
If disabled, a command may only be run after the
audit event is successfully written. This flag
is only effective on systems for which sudoers
supports audit logging, including FreeBSD, Linux,
macOS and Solaris. This flag is on by default.
ignore_dot If set, sudo will ignore "." or "" (both denoting
current directory) in the PATH environment
variable; the PATH itself is not modified. This
flag is off by default.
ignore_iolog_errors
Allow commands to be run even if sudoers cannot
write to the I/O log (local or remote). If
enabled, an I/O log write failure is not treated
as a fatal error. If disabled, the command will
be terminated if the I/O log cannot be written
to. This flag is off by default.
ignore_logfile_errors
Allow commands to be run even if sudoers cannot
write to the log file. If enabled, a log file
write failure is not treated as a fatal error.
If disabled, a command may only be run after the
log file entry is successfully written. This
flag only has an effect when sudoers is
configured to use file-based logging via the
logfile setting. This flag is on by default.
ignore_local_sudoers
If set via LDAP, parsing of /etc/sudoers will be
skipped. This is intended for Enterprises that
wish to prevent the usage of local sudoers files
so that only LDAP is used. This thwarts the
efforts of rogue operators who would attempt to
add roles to /etc/sudoers. When this flag is
enabled, /etc/sudoers does not even need to
exist. Since this flag tells sudo how to behave
when no specific LDAP entries have been matched,
this sudoOption is only meaningful for the
cn=defaults section. This flag is off by
default.
ignore_unknown_defaults
If set, sudo will not produce a warning if it
encounters an unknown Defaults entry in the
sudoers file or an unknown sudoOption in LDAP.
This flag is off by default.
insults If set, sudo will insult users when they enter an
incorrect password. This flag is off by default.
log_allowed If set, sudoers will log commands allowed by the
policy to the system audit log (where supported)
as well as to syslog and/or a log file. This
flag is on by default.
This setting is only supported by version 1.8.29
or higher.
log_denied If set, sudoers will log commands denied by the
policy to the system audit log (where supported)
as well as to syslog and/or a log file. This
flag is on by default.
This setting is only supported by version 1.8.29
or higher.
log_host If set, the host name will be included in log
entries written to the file configured by the
logfile setting. This flag is off by default.
log_input If set, sudo will run the command in a pseudo-
terminal and log all user input. If the standard
input is not connected to the user's tty, due to
I/O redirection or because the command is part of
a pipeline, that input is also captured and
stored in a separate log file. Anything sent to
the standard input will be consumed, regardless
of whether or not the command run via sudo is
actually reading the standard input. This may
have unexpected results when using sudo in a
shell script that expects to process the standard
input. For more information about I/O logging,
see the I/O LOG FILES section. This flag is off
by default.
log_output If set, sudo will run the command in a pseudo-
terminal and log all output that is sent to the
screen, similar to the script(1) command. For
more information about I/O logging, see the I/O
LOG FILES section. This flag is off by default.
log_server_keepalive
If set, sudo will enable the TCP keepalive socket
option on the connection to the log server. This
enables the periodic transmission of keepalive
messages to the server. If the server does not
respond to a message, the connection will be
closed and the running command will be terminated
unless the ignore_iolog_errors flag (I/O logging
enabled) or the ignore_log_errors flag (I/O
logging disabled) is set. This flag is on by
default.
This setting is only supported by version 1.9.0
or higher.
log_server_verify
If set, the server certificate received during
the TLS handshake must be valid and it must
contain either the server name (from log_servers)
or its IP address. If either of these conditions
is not met, the TLS handshake will fail. This
flag is on by default.
This setting is only supported by version 1.9.0
or higher.
log_year If set, the four-digit year will be logged in the
(non-syslog) sudo log file. This flag is off by
default.
long_otp_prompt When validating with a One Time Password (OTP)
scheme such as S/Key or OPIE, a two-line prompt
is used to make it easier to cut and paste the
challenge to a local window. It's not as pretty
as the default but some people find it more
convenient. This flag is off by default.
mail_all_cmnds Send mail to the mailto user every time a user
attempts to run a command via sudo (this includes
sudoedit). No mail will be sent if the user runs
sudo with the -l or -v option unless there is an
authentication error and the mail_badpass flag is
also set. This flag is off by default.
mail_always Send mail to the mailto user every time a user
runs sudo. This flag is off by default.
mail_badpass Send mail to the mailto user if the user running
sudo does not enter the correct password. If the
command the user is attempting to run is not
permitted by sudoers and one of the
mail_all_cmnds, mail_always, mail_no_host,
mail_no_perms or mail_no_user flags are set, this
flag will have no effect. This flag is off by
default.
mail_no_host If set, mail will be sent to the mailto user if
the invoking user exists in the sudoers file, but
is not allowed to run commands on the current
host. This flag is off by default.
mail_no_perms If set, mail will be sent to the mailto user if
the invoking user is allowed to use sudo but the
command they are trying is not listed in their
sudoers file entry or is explicitly denied. This
flag is off by default.
mail_no_user If set, mail will be sent to the mailto user if
the invoking user is not in the sudoers file.
This flag is on by default.
match_group_by_gid
By default, sudoers will look up each group the
user is a member of by group-ID to determine the
group name (this is only done once). The
resulting list of the user's group names is used
when matching groups listed in the sudoers file.
This works well on systems where the number of
groups listed in the sudoers file is larger than
the number of groups a typical user belongs to.
On systems where group lookups are slow, where
users may belong to a large number of groups, and
where the number of groups listed in the sudoers
file is relatively small, it may be prohibitively
expensive and running commands via sudo may take
longer than normal. On such systems it may be
faster to use the match_group_by_gid flag to
avoid resolving the user's group-IDs to group
names. In this case, sudoers must look up any
group name listed in the sudoers file and use the
group-ID instead of the group name when
determining whether the user is a member of the
group.
Note that if match_group_by_gid is enabled, group
database lookups performed by sudoers will be
keyed by group name as opposed to group-ID. On
systems where there are multiple sources for the
group database, it is possible to have
conflicting group names or group-IDs in the local
/etc/group file and the remote group database.
On such systems, enabling or disabling
match_group_by_gid can be used to choose whether
group database queries are performed by name
(enabled) or ID (disabled), which may aid in
working around group entry conflicts.
The match_group_by_gid flag has no effect when
sudoers data is stored in LDAP. This flag is off
by default.
This setting is only supported by version 1.8.18
or higher.
netgroup_tuple If set, netgroup lookups will be performed using
the full netgroup tuple: host name, user name and
domain (if one is set). Historically, sudo only
matched the user name and domain for netgroups
used in a User_List and only matched the host
name and domain for netgroups used in a
Host_List. This flag is off by default.
noexec If set, all commands run via sudo will behave as
if the NOEXEC tag has been set, unless overridden
by an EXEC tag. See the description of EXEC and
NOEXEC above as well as the Preventing shell
escapes section at the end of this manual. This
flag is off by default.
pam_acct_mgmt On systems that use PAM for authentication, sudo
will perform PAM account validation for the
invoking user by default. The actual checks
performed depend on which PAM modules are
configured. If enabled, account validation will
be performed regardless of whether or not a
password is required. This flag is on by
default.
This setting is only supported by version 1.8.28
or higher.
pam_rhost On systems that use PAM for authentication, sudo
will set the PAM remote host value to the name of
the local host when the pam_rhost flag is
enabled. On Linux systems, enabling pam_rhost
may result in DNS lookups of the local host name
when PAM is initialized. On Solaris versions
prior to Solaris 8, pam_rhost must be enabled if
pam_ruser is also enabled to avoid a crash in the
Solaris PAM implementation.
This flag is off by default on systems other than
Solaris.
This setting is only supported by version 1.9.0
or higher.
pam_ruser On systems that use PAM for authentication, sudo
will set the PAM remote user value to the name of
the user that invoked sudo when the pam_ruser
flag is enabled. This flag is on by default.
This setting is only supported by version 1.9.0
or higher.
pam_session On systems that use PAM for authentication, sudo
will create a new PAM session for the command to
be run in. Unless sudo is given the -i or -s
options, PAM session modules are run with the
“silent” flag enabled. This prevents last login
information from being displayed for every
command on some systems. Disabling pam_session
may be needed on older PAM implementations or on
operating systems where opening a PAM session
changes the utmp or wtmp files. If PAM session
support is disabled, resource limits may not be
updated for the command being run. If
pam_session, pam_setcred, and use_pty are
disabled, log_servers has not been set and I/O
logging has not been configured, sudo will
execute the command directly instead of running
it as a child process. This flag is on by
default.
This setting is only supported by version 1.8.7
or higher.
pam_setcred On systems that use PAM for authentication, sudo
will attempt to establish credentials for the
target user by default, if supported by the
underlying authentication system. One example of
a credential is a Kerberos ticket. If
pam_session, pam_setcred, and use_pty are
disabled, log_servers has not been set and I/O
logging has not been configured, sudo will
execute the command directly instead of running
it as a child process. This flag is on by
default.
This setting is only supported by version 1.8.8
or higher.
passprompt_override
If set, the prompt specified by passprompt or the
SUDO_PROMPT environment variable will always be
used and will replace the prompt provided by a
PAM module or other authentication method. This
flag is off by default.
path_info Normally, sudo will tell the user when a command
could not be found in their PATH environment
variable. Some sites may wish to disable this as
it could be used to gather information on the
location of executables that the normal user does
not have access to. The disadvantage is that if
the executable is simply not in the user's PATH,
sudo will tell the user that they are not allowed
to run it, which can be confusing. This flag is
on by default.
preserve_groups By default, sudo will initialize the group vector
to the list of groups the target user is in.
When preserve_groups is set, the user's existing
group vector is left unaltered. The real and
effective group-IDs, however, are still set to
match the target user. This flag is off by
default.
pwfeedback By default, sudo reads the password like most
other Unix programs, by turning off echo until
the user hits the return (or enter) key. Some
users become confused by this as it appears to
them that sudo has hung at this point. When
pwfeedback is set, sudo will provide visual
feedback when the user presses a key. Note that
this does have a security impact as an onlooker
may be able to determine the length of the
password being entered. This flag is off by
default.
requiretty If set, sudo will only run when the user is
logged in to a real tty. When this flag is set,
sudo can only be run from a login session and not
via other means such as cron(8) or cgi-bin
scripts. This flag is off by default.
root_sudo If set, root is allowed to run sudo too.
Disabling this prevents users from “chaining”
sudo commands to get a root shell by doing
something like “sudo sudo /bin/sh”. Note,
however, that turning off root_sudo will also
prevent root from running sudoedit. Disabling
root_sudo provides no real additional security;
it exists purely for historical reasons. This
flag is on by default.
rootpw If set, sudo will prompt for the root password
instead of the password of the invoking user when
running a command or editing a file. This flag
is off by default.
runas_allow_unknown_id
If enabled, allow matching of runas user and
group IDs that are not present in the password or
group databases. In addition to explicitly
matching unknown user or group IDs in a
Runas_List, this option also allows the ALL alias
to match unknown IDs. This flag is off by
default.
This setting is only supported by version 1.8.30
or higher. Older versions of sudo always allowed
matching of unknown user and group IDs.
runas_check_shell
If enabled, sudo will only run commands as a user
whose shell appears in the /etc/shells file, even
if the invoking user's Runas_List would otherwise
permit it. If no /etc/shells file is present, a
system-dependent list of built-in default shells
is used. On many operating systems, system users
such as “bin”, do not have a valid shell and this
flag can be used to prevent commands from being
run as those users. This flag is off by default.
This setting is only supported by version 1.8.30
or higher.
runaspw If set, sudo will prompt for the password of the
user defined by the runas_default option
(defaults to root) instead of the password of the
invoking user when running a command or editing a
file. This flag is off by default.
set_home If enabled and sudo is invoked with the -s
option, the HOME environment variable will be set
to the home directory of the target user (which
is the root user unless the -u option is used).
This flag is largely obsolete and has no effect
unless the env_reset flag has been disabled or
HOME is present in the env_keep list, both of
which are strongly discouraged. This flag is off
by default.
set_logname Normally, sudo will set the LOGNAME and USER
environment variables to the name of the target
user (usually root unless the -u option is
given). However, since some programs (including
the RCS revision control system) use LOGNAME to
determine the real identity of the user, it may
be desirable to change this behavior. This can
be done by negating the set_logname option. Note
that set_logname will have no effect if the
env_reset option has not been disabled and the
env_keep list contains LOGNAME or USER. This
flag is on by default.
set_utmp When enabled, sudo will create an entry in the
utmp (or utmpx) file when a pseudo-terminal is
allocated. A pseudo-terminal is allocated by
sudo when it is running in a terminal and one or
more of the log_input, log_output or use_pty
flags is enabled. By default, the new entry will
be a copy of the user's existing utmp entry (if
any), with the tty, time, type and pid fields
updated. This flag is on by default.
setenv Allow the user to disable the env_reset option
from the command line via the -E option.
Additionally, environment variables set via the
command line are not subject to the restrictions
imposed by env_check, env_delete, or env_keep.
As such, only trusted users should be allowed to
set variables in this manner. This flag is off
by default.
shell_noargs If set and sudo is invoked with no arguments it
acts as if the -s option had been given. That
is, it runs a shell as root (the shell is
determined by the SHELL environment variable if
it is set, falling back on the shell listed in
the invoking user's /etc/passwd entry if not).
This flag is off by default.
stay_setuid Normally, when sudo executes a command the real
and effective UIDs are set to the target user
(root by default). This option changes that
behavior such that the real UID is left as the
invoking user's UID. In other words, this makes
sudo act as a set-user-ID wrapper. This can be
useful on systems that disable some potentially
dangerous functionality when a program is run
set-user-ID. This option is only effective on
systems that support either the setreuid(2) or
setresuid(2) system call. This flag is off by
default.
sudoedit_checkdir
If set, sudoedit will check all directory
components of the path to be edited for
writability by the invoking user. Symbolic links
will not be followed in writable directories and
sudoedit will refuse to edit a file located in a
writable directory. These restrictions are not
enforced when sudoedit is run by root. On some
systems, if all directory components of the path
to be edited are not readable by the target user,
sudoedit will be unable to edit the file. This
flag is on by default.
This setting was first introduced in version
1.8.15 but initially suffered from a race
condition. The check for symbolic links in
writable intermediate directories was added in
version 1.8.16.
sudoedit_follow By default, sudoedit will not follow symbolic
links when opening files. The sudoedit_follow
option can be enabled to allow sudoedit to open
symbolic links. It may be overridden on a per-
command basis by the FOLLOW and NOFOLLOW tags.
This flag is off by default.
This setting is only supported by version 1.8.15
or higher.
syslog_pid When logging via syslog(3), include the process
ID in the log entry. This flag is off by
default.
This setting is only supported by version 1.8.21
or higher.
targetpw If set, sudo will prompt for the password of the
user specified by the -u option (defaults to
root) instead of the password of the invoking
user when running a command or editing a file.
Note that this flag precludes the use of a user-
ID not listed in the passwd database as an
argument to the -u option. This flag is off by
default.
tty_tickets If set, users must authenticate on a per-tty
basis. With this flag enabled, sudo will use a
separate record in the time stamp file for each
terminal. If disabled, a single record is used
for all login sessions.
This option has been superseded by the
timestamp_type option.
umask_override If set, sudo will set the umask as specified in
the sudoers file without modification. This
makes it possible to specify a umask in the
sudoers file that is more permissive than the
user's own umask and matches historical behavior.
If umask_override is not set, sudo will set the
umask to be the union of the user's umask and
what is specified in sudoers. This flag is off
by default.
use_netgroups If set, netgroups (prefixed with ‘+’), may be
used in place of a user or host. For LDAP-based
sudoers, netgroup support requires an expensive
sub-string match on the server unless the
NETGROUP_BASE directive is present in the
/etc/ldap.conf file. If netgroups are not
needed, this option can be disabled to reduce the
load on the LDAP server. This flag is on by
default.
use_pty If set, and sudo is running in a terminal, the
command will be run in a pseudo-terminal (even if
no I/O logging is being done). If the sudo
process is not attached to a terminal, use_pty
has no effect.
A malicious program run under sudo may be capable
of injecting commands into the user's terminal or
running a background process that retains access
to the user's terminal device even after the main
program has finished executing. By running the
command in a separate pseudo-terminal, this
attack is no longer possible. This flag is off
by default.
user_command_timeouts
If set, the user may specify a timeout on the
command line. If the timeout expires before the
command has exited, the command will be
terminated. If a timeout is specified both in
the sudoers file and on the command line, the
smaller of the two timeouts will be used. See
the Timeout_Spec section for a description of the
timeout syntax. This flag is off by default.
This setting is only supported by version 1.8.20
or higher.
utmp_runas If set, sudo will store the name of the runas
user when updating the utmp (or utmpx) file. By
default, sudo stores the name of the invoking
user. This flag is off by default.
visiblepw By default, sudo will refuse to run if the user
must enter a password but it is not possible to
disable echo on the terminal. If the visiblepw
flag is set, sudo will prompt for a password even
when it would be visible on the screen. This
makes it possible to run things like “ssh
somehost sudo ls” since by default, ssh(1) does
not allocate a tty when running a command. This
flag is off by default.
Integers:
closefrom Before it executes a command, sudo will close all
open file descriptors other than standard input,
standard output and standard error (ie: file
descriptors 0-2). The closefrom option can be
used to specify a different file descriptor at
which to start closing. The default is 3.
command_timeout The maximum amount of time a command is allowed
to run before it is terminated. See the
Timeout_Spec section for a description of the
timeout syntax.
This setting is only supported by version 1.8.20
or higher.
log_server_timeout
The maximum amount of time to wait when
connecting to a log server or waiting for a
server response. See the Timeout_Spec section
for a description of the timeout syntax. The
default value is 30 seconds.
This setting is only supported by version 1.9.0
or higher.
maxseq The maximum sequence number that will be
substituted for the “%{seq}” escape in the I/O
log file (see the iolog_dir description below for
more information). While the value substituted
for “%{seq}” is in base 36, maxseq itself should
be expressed in decimal. Values larger than
2176782336 (which corresponds to the base 36
sequence number “ZZZZZZ”) will be silently
truncated to 2176782336. The default value is
2176782336.
Once the local sequence number reaches the value
of maxseq, it will “roll over” to zero, after
which sudoers will truncate and re-use any
existing I/O log path names.
This setting is only supported by version 1.8.7
or higher.
passwd_tries The number of tries a user gets to enter his/her
password before sudo logs the failure and exits.
The default is 3.
syslog_maxlen On many systems, syslog(3) has a relatively small
log buffer. IETF RFC 5424 states that syslog
servers must support messages of at least 480
bytes and should support messages up to 2048
bytes. By default, sudoers creates log messages
up to 980 bytes which corresponds to the historic
BSD syslog implementation which used a 1024 byte
buffer to store the message, date, hostname and
program name. To prevent syslog messages from
being truncated, sudoers will split up log
messages that are larger than syslog_maxlen
bytes. When a message is split, additional parts
will include the string “(command continued)”
after the user name and before the continued
command line arguments.
This setting is only supported by version 1.8.19
or higher.
Integers that can be used in a boolean context:
loglinelen Number of characters per line for the file log.
This value is used to decide when to wrap lines
for nicer log files. This has no effect on the
syslog log file, only the file log. The default
is 80 (use 0 or negate the option to disable word
wrap).
passwd_timeout Number of minutes before the sudo password prompt
times out, or 0 for no timeout. The timeout may
include a fractional component if minute
granularity is insufficient, for example 2.5.
The default is 5.
timestamp_timeout
Number of minutes that can elapse before sudo
will ask for a passwd again. The timeout may
include a fractional component if minute
granularity is insufficient, for example 2.5.
The default is 5. Set this to 0 to always prompt
for a password. If set to a value less than 0
the user's time stamp will not expire until the
system is rebooted. This can be used to allow
users to create or delete their own time stamps
via “sudo -v” and “sudo -k” respectively.
umask File mode creation mask to use when running the
command. Negate this option or set it to 0777 to
prevent sudoers from changing the umask. Unless
the umask_override flag is set, the actual umask
will be the union of the user's umask and the
value of the umask setting, which defaults to
0022. This guarantees that sudo never lowers the
umask when running a command.
If umask is explicitly set in sudoers, it will
override any umask setting in PAM or login.conf.
If umask is not set in sudoers, the umask
specified by PAM or login.conf will take
precedence. The umask setting in PAM is not used
for sudoedit, which does not create a new PAM
session.
Strings:
authfail_message Message that is displayed after a user fails to
authenticate. The message may include the ‘%d’
escape which will expand to the number of failed
password attempts. If set, it overrides the
default message, %d incorrect password
attempt(s).
badpass_message Message that is displayed if a user enters an
incorrect password. The default is Sorry, try
again. unless insults are enabled.
editor A colon (‘:’) separated list of editors path
names used by sudoedit and visudo. For sudoedit,
this list is used to find an editor when none of
the SUDO_EDITOR, VISUAL or EDITOR environment
variables are set to an editor that exists and is
executable. For visudo, it is used as a white
list of allowed editors; visudo will choose the
editor that matches the user's SUDO_EDITOR,
VISUAL or EDITOR environment variable if
possible, or the first editor in the list that
exists and is executable if not. Unless invoked
as sudoedit, sudo does not preserve the
SUDO_EDITOR, VISUAL or EDITOR environment
variables unless they are present in the env_keep
list or the env_reset option is disabled. The
default is vi.
iolog_dir The top-level directory to use when constructing
the path name for the input/output log directory.
Only used if the log_input or log_output options
are enabled or when the LOG_INPUT or LOG_OUTPUT
tags are present for a command. The session
sequence number, if any, is stored in the
directory. The default is /var/log/sudo-io.
The following percent (‘%’) escape sequences are
supported:
%{seq}
expanded to a monotonically increasing
base-36 sequence number, such as 0100A5,
where every two digits are used to form a
new directory, e.g., 01/00/A5
%{user}
expanded to the invoking user's login name
%{group}
expanded to the name of the invoking user's
real group-ID
%{runas_user}
expanded to the login name of the user the
command will be run as (e.g., root)
%{runas_group}
expanded to the group name of the user the
command will be run as (e.g., wheel)
%{hostname}
expanded to the local host name without the
domain name
%{command}
expanded to the base name of the command
being run
In addition, any escape sequences supported by
the system's strftime(3) function will be
expanded.
To include a literal ‘%’ character, the string
‘%%’ should be used.
iolog_file The path name, relative to iolog_dir, in which to
store input/output logs when the log_input or
log_output options are enabled or when the
LOG_INPUT or LOG_OUTPUT tags are present for a
command. Note that iolog_file may contain
directory components. The default is “%{seq}”.
See the iolog_dir option above for a list of
supported percent (‘%’) escape sequences.
In addition to the escape sequences, path names
that end in six or more Xs will have the Xs
replaced with a unique combination of digits and
letters, similar to the mktemp(3) function.
If the path created by concatenating iolog_dir
and iolog_file already exists, the existing I/O
log file will be truncated and overwritten unless
iolog_file ends in six or more Xs.
iolog_flush If set, sudo will flush I/O log data to disk
after each write instead of buffering it. This
makes it possible to view the logs in real-time
as the program is executing but may significantly
reduce the effectiveness of I/O log compression.
This flag is off by default.
This setting is only supported by version 1.8.20
or higher.
iolog_group The group name to look up when setting the group-
ID on new I/O log files and directories. If
iolog_group is not set, the primary group-ID of
the user specified by iolog_user is used. If
neither iolog_group nor iolog_user are set, I/O
log files and directories are created with group-
ID 0.
This setting is only supported by version 1.8.19
or higher.
iolog_mode The file mode to use when creating I/O log files.
Mode bits for read and write permissions for
owner, group or other are honored, everything
else is ignored. The file permissions will
always include the owner read and write bits,
even if they are not present in the specified
mode. When creating I/O log directories, search
(execute) bits are added to match the read and
write bits specified by iolog_mode. Defaults to
0600 (read and write by user only).
This setting is only supported by version 1.8.19
or higher.
iolog_user The user name to look up when setting the user
and group-IDs on new I/O log files and
directories. If iolog_group is set, it will be
used instead of the user's primary group-ID. By
default, I/O log files and directories are
created with user and group-ID 0.
This setting can be useful when the I/O logs are
stored on a Network File System (NFS) share.
Having a dedicated user own the I/O log files
means that sudoers does not write to the log
files as user-ID 0, which is usually not
permitted by NFS.
This setting is only supported by version 1.8.19
or higher.
lecture_status_dir
The directory in which sudo stores per-user
lecture status files. Once a user has received
the lecture, a zero-length file is created in
this directory so that sudo will not lecture the
user again. This directory should not be cleared
when the system reboots. The default is
/var/db/sudo/lectured.
log_server_cabundle
The path to a certificate authority bundle file,
in PEM format, to use instead of the system's
default certificate authority database when
authenticating the log server. The default is to
use the system's default certificate authority
database. This setting has no effect unless
log_servers is set and the remote log server is
secured with TLS.
This setting is only supported by version 1.9.0
or higher.
log_server_peer_cert
The path to the client's certificate file, in PEM
format. This setting is required when
log_servers is set and the remote log server is
secured with TLS.
This setting is only supported by version 1.9.0
or higher.
log_server_peer_key
The path to the client's private key file, in PEM
format. This setting is required when
log_servers is set and the remote log server is
secured with TLS.
This setting is only supported by version 1.9.0
or higher.
mailsub Subject of the mail sent to the mailto user. The
escape %h will expand to the host name of the
machine. Default is “*** SECURITY information
for %h ***”.
noexec_file As of sudo version 1.8.1 this option is no longer
supported. The path to the noexec file should
now be set in the sudo.conf(5) file.
pam_login_service
On systems that use PAM for authentication, this
is the service name used when the -i option is
specified. The default value is “sudo”. See the
description of pam_service for more information.
This setting is only supported by version 1.8.8
or higher.
pam_service On systems that use PAM for authentication, the
service name specifies the PAM policy to apply.
This usually corresponds to an entry in the
pam.conf file or a file in the /etc/pam.d
directory. The default value is “sudo”.
This setting is only supported by version 1.8.8
or higher.
passprompt The default prompt to use when asking for a
password; can be overridden via the -p option or
the SUDO_PROMPT environment variable. The
following percent (‘%’) escape sequences are
supported:
%H expanded to the local host name including
the domain name (only if the machine's host
name is fully qualified or the fqdn option
is set)
%h expanded to the local host name without the
domain name
%p expanded to the user whose password is
being asked for (respects the rootpw,
targetpw and runaspw flags in sudoers)
%U expanded to the login name of the user the
command will be run as (defaults to root)
%u expanded to the invoking user's login name
%% two consecutive % characters are collapsed
into a single % character
On systems that use PAM for authentication,
passprompt will only be used if the prompt
provided by the PAM module matches the string
“Password: ” or “username's Password: ”. This
ensures that the passprompt setting does not
interfere with challenge-response style
authentication. The passprompt_override flag can
be used to change this behavior.
The default value is “Password: ”.
runas_default The default user to run commands as if the -u
option is not specified on the command line.
This defaults to root.
sudoers_locale Locale to use when parsing the sudoers file,
logging commands, and sending email. Note that
changing the locale may affect how sudoers is
interpreted. Defaults to “C”.
timestamp_type sudoers uses per-user time stamp files for
credential caching. The timestamp_type option
can be used to specify the type of time stamp
record used. It has the following possible
values:
global A single time stamp record is used for
all of a user's login sessions,
regardless of the terminal or parent
process ID. An additional record is used
to serialize password prompts when sudo
is used multiple times in a pipeline, but
this does not affect authentication.
ppid A single time stamp record is used for
all processes with the same parent
process ID (usually the shell). Commands
run from the same shell (or other common
parent process) will not require a
password for timestamp_timeout minutes (5
by default). Commands run via sudo with
a different parent process ID, for
example from a shell script, will be
authenticated separately.
tty One time stamp record is used for each
terminal, which means that a user's login
sessions are authenticated separately.
If no terminal is present, the behavior
is the same as ppid. Commands run from
the same terminal will not require a
password for timestamp_timeout minutes (5
by default).
kernel The time stamp is stored in the kernel as
an attribute of the terminal device. If
no terminal is present, the behavior is
the same as ppid. Negative
timestamp_timeout values are not
supported and positive values are limited
to a maximum of 60 minutes. This is
currently only supported on OpenBSD.
The default value is tty.
This setting is only supported by version 1.8.21
or higher.
timestampdir The directory in which sudo stores its time stamp
files. This directory should be cleared when the
system reboots. The default is /run/sudo/ts.
timestampowner The owner of the lecture status directory, time
stamp directory and all files stored therein.
The default is root.
Strings that can be used in a boolean context:
env_file The env_file option specifies the fully qualified
path to a file containing variables to be set in the
environment of the program being run. Entries in
this file should either be of the form
“VARIABLE=value” or “export VARIABLE=value”. The
value may optionally be enclosed in single or double
quotes. Variables in this file are only added if the
variable does not already exist in the environment.
This file is considered to be part of the security
policy, its contents are not subject to other sudo
environment restrictions such as env_keep and
env_check.
exempt_group Users in this group are exempt from password and PATH
requirements. The group name specified should not
include a % prefix. This is not set by default.
fdexec Determines whether sudo will execute a command by its
path or by an open file descriptor. It has the
following possible values:
always Always execute by file descriptor.
never Never execute by file descriptor.
digest_only
Only execute by file descriptor if the
command has an associated digest in the
sudoers file.
The default value is digest_only. This avoids a time
of check versus time of use race condition when the
command is located in a directory writable by the
invoking user.
Note that fdexec will change the first element of the
argument vector for scripts ($0 in the shell) due to
the way the kernel runs script interpreters. Instead
of being a normal path, it will refer to a file
descriptor. For example, /dev/fd/4 on Solaris and
/proc/self/fd/4 on Linux. A workaround is to use the
SUDO_COMMAND environment variable instead.
The fdexec setting is only used when the command is
matched by path name. It has no effect if the
command is matched by the built-in ALL alias.
This setting is only supported by version 1.8.20 or
higher. If the operating system does not support the
fexecve(2) system call, this setting has no effect.
group_plugin A string containing a sudoers group plugin with
optional arguments. The string should consist of the
plugin path, either fully-qualified or relative to
the /usr/local/libexec/sudo directory, followed by
any configuration arguments the plugin requires.
These arguments (if any) will be passed to the
plugin's initialization function. If arguments are
present, the string must be enclosed in double quotes
("").
For more information see GROUP PROVIDER PLUGINS.
lecture This option controls when a short lecture will be
printed along with the password prompt. It has the
following possible values:
always Always lecture the user.
never Never lecture the user.
once Only lecture the user the first time they run
sudo.
If no value is specified, a value of once is implied.
Negating the option results in a value of never being
used. The default value is once.
lecture_file Path to a file containing an alternate sudo lecture
that will be used in place of the standard lecture if
the named file exists. By default, sudo uses a
built-in lecture.
listpw This option controls when a password will be required
when a user runs sudo with the -l option. It has the
following possible values:
all All the user's sudoers file entries for the
current host must have the NOPASSWD flag
set to avoid entering a password.
always The user must always enter a password to
use the -l option.
any At least one of the user's sudoers file
entries for the current host must have the
NOPASSWD flag set to avoid entering a
password.
never The user need never enter a password to use
the -l option.
If no value is specified, a value of any is implied.
Negating the option results in a value of never being
used. The default value is any.
log_format The event log format. Supported log formats are:
json Logs in JSON format. JSON log entries
contain the full user details as well as
the execution environment if the command
was allowed. Due to limitations of the
protocol, JSON events sent via syslog may
be truncated.
sudo Traditional sudo-style logs, see LOG FORMAT
for a description of the log file format.
This setting affects logs sent via syslog(3) as well
as the file specified by the logfile setting, if any.
The default value is sudo.
logfile Path to the sudo log file (not the syslog log file).
Setting a path turns on logging to a file; negating
this option turns it off. By default, sudo logs via
syslog.
mailerflags Flags to use when invoking mailer. Defaults to -t.
mailerpath Path to mail program used to send warning mail.
Defaults to the path to sendmail found at configure
time.
mailfrom Address to use for the “from” address when sending
warning and error mail. The address should be
enclosed in double quotes ("") to protect against
sudo interpreting the @ sign. Defaults to the name
of the user running sudo.
mailto Address to send warning and error mail to. The
address should be enclosed in double quotes ("") to
protect against sudo interpreting the @ sign.
Defaults to root.
restricted_env_file
The restricted_env_file option specifies the fully
qualified path to a file containing variables to be
set in the environment of the program being run.
Entries in this file should either be of the form
“VARIABLE=value” or “export VARIABLE=value”. The
value may optionally be enclosed in single or double
quotes. Variables in this file are only added if the
variable does not already exist in the environment.
Unlike env_file, the file's contents are not trusted
and are processed in a manner similar to that of the
invoking user's environment. If env_reset is
enabled, variables in the file will only be added if
they are matched by either the env_check or env_keep
list. If env_reset is disabled, variables in the
file are added as long as they are not matched by the
env_delete list. In either case, the contents of
restricted_env_file are processed before the contents
of env_file.
runchroot If set, sudo will use this value for the root
directory when running a command. The special value
“*” will allow the user to specify the root directory
via sudo's -R option. See the Chroot_Spec section
for more details.
It is only possible to use runchroot as a command-
specific Defaults setting if the command exists with
the same path both inside and outside the chroot
jail. This restriction does not apply to generic,
host or user-based Defaults settings or to a
Cmnd_Spec that includes a Chroot_Spec.
This setting is only supported by version 1.9.3 or
higher.
runcwd If set, sudo will use this value for the working
directory when running a command. The special value
“*” will allow the user to specify the working
directory via sudo's -D option. See the Chdir_Spec
section for more details.
This setting is only supported by version 1.9.3 or
higher.
secure_path If set, sudo will use this value in place of the
user's PATH environment variable. This option can be
used to reset the PATH to a known good value that
contains directories for system administrator
commands such as /usr/sbin.
Users in the group specified by the exempt_group
option are not affected by secure_path. This option
is not set by default.
syslog Syslog facility if syslog is being used for logging
(negate to disable syslog logging). Defaults to
authpriv.
The following syslog facilities are supported:
authpriv (if your OS supports it), auth, daemon,
user, local0, local1, local2, local3, local4, local5,
local6, and local7.
syslog_badpri
Syslog priority to use when the user is not allowed
to run a command or when authentication is
unsuccessful. Defaults to alert.
The following syslog priorities are supported: alert,
crit, debug, emerg, err, info, notice, warning, and
none. Negating the option or setting it to a value
of none will disable logging of unsuccessful
commands.
syslog_goodpri
Syslog priority to use when the user is allowed to
run a command and authentication is successful.
Defaults to notice.
See syslog_badpri for the list of supported syslog
priorities. Negating the option or setting it to a
value of none will disable logging of successful
commands.
verifypw This option controls when a password will be required
when a user runs sudo with the -v option. It has the
following possible values:
all All the user's sudoers file entries for the
current host must have the NOPASSWD flag set
to avoid entering a password.
always The user must always enter a password to use
the -v option.
any At least one of the user's sudoers file
entries for the current host must have the
NOPASSWD flag set to avoid entering a
password.
never The user need never enter a password to use
the -v option.
If no value is specified, a value of all is implied.
Negating the option results in a value of never being
used. The default value is all.
Lists that can be used in a boolean context:
env_check Environment variables to be removed from the
user's environment unless they are considered
“safe”. For all variables except TZ, “safe”
means that the variable's value does not contain
any ‘%’ or ‘/’ characters. This can be used to
guard against printf-style format vulnerabilities
in poorly-written programs. The TZ variable is
considered unsafe if any of the following are
true:
• It consists of a fully-qualified path name,
optionally prefixed with a colon (‘:’), that
does not match the location of the zoneinfo
directory.
• It contains a .. path element.
• It contains white space or non-printable
characters.
• It is longer than the value of PATH_MAX.
The argument may be a double-quoted, space-
separated list or a single value without double-
quotes. The list can be replaced, added to,
deleted from, or disabled by using the =, +=, -=,
and ! operators respectively. Regardless of
whether the env_reset option is enabled or
disabled, variables specified by env_check will
be preserved in the environment if they pass the
aforementioned check. The global list of
environment variables to check is displayed when
sudo is run by root with the -V option.
env_delete Environment variables to be removed from the
user's environment when the env_reset option is
not in effect. The argument may be a double-
quoted, space-separated list or a single value
without double-quotes. The list can be replaced,
added to, deleted from, or disabled by using the
=, +=, -=, and ! operators respectively. The
global list of environment variables to remove is
displayed when sudo is run by root with the -V
option. Note that many operating systems will
remove potentially dangerous variables from the
environment of any set-user-ID process (such as
sudo).
env_keep Environment variables to be preserved in the
user's environment when the env_reset option is
in effect. This allows fine-grained control over
the environment sudo-spawned processes will
receive. The argument may be a double-quoted,
space-separated list or a single value without
double-quotes. The list can be replaced, added
to, deleted from, or disabled by using the =, +=,
-=, and ! operators respectively. The global
list of variables to keep is displayed when sudo
is run by root with the -V option.
Preserving the HOME environment variable has
security implications since many programs use it
when searching for configuration or data files.
Adding HOME to env_keep may enable a user to run
unrestricted commands via sudo and is strongly
discouraged. Users wishing to edit files with
sudo should run sudoedit (or sudo -e) to get
their accustomed editor configuration instead of
invoking the editor directly.
log_servers A list of one or more servers to use for remote
event and I/O log storage, separated by white
space. Log servers must be running sudo_logsrvd
or another service that implements the protocol
described by sudo_logsrv.proto(5).
Server addresses should be of the form
“host[:port][(tls)]”. The host portion may be a
host name, an IPv4 address, or an IPv6 address in
square brackets.
If the optional tls flag is present, the
connection will be secured with Transport Layer
Security (TLS) version 1.2 or 1.3. Versions of
TLS prior to 1.2 are not supported.
If a port is specified, it may either be a port
number or a well-known service name as defined by
the system service name database. If no port is
specified, port 30343 will be used for plaintext
connections and port 30344 will be used for TLS
connections.
When log_servers is set, event log data will be
logged both locally (see the syslog and log_file
settings) as well as remotely, but I/O log data
will only be logged remotely. If multiple hosts
are specified, they will be attempted in reverse
order. If no log servers are available, the user
will not be able to run a command unless either
the ignore_iolog_errors flag (I/O logging
enabled) or the ignore_log_errors flag (I/O
logging disabled) is set. Likewise, if the
connection to the log server is interrupted while
sudo is running, the command will be terminated
unless the ignore_iolog_errors flag (I/O logging
enabled) or the ignore_log_errors flag (I/O
logging disabled) is set.
This setting is only supported by version 1.9.0
or higher.
The sudoers plugin supports its own plugin interface to allow non-
Unix group lookups which can query a group source other than the
standard Unix group database. This can be used to implement
support for the nonunix_group syntax described earlier.
Group provider plugins are specified via the group_plugin setting.
The argument to group_plugin should consist of the plugin path,
either fully-qualified or relative to the /usr/local/libexec/sudo
directory, followed by any configuration options the plugin
requires. These options (if specified) will be passed to the
plugin's initialization function. If options are present, the
string must be enclosed in double quotes ("").
The following group provider plugins are installed by default:
group_file
The group_file plugin supports an alternate group file
that uses the same syntax as the /etc/group file. The
path to the group file should be specified as an option
to the plugin. For example, if the group file to be used
is /etc/sudo-group:
Defaults group_plugin="group_file.so /etc/sudo-group"
system_group
The system_group plugin supports group lookups via the
standard C library functions getgrnam() and getgrid().
This plugin can be used in instances where the user
belongs to groups not present in the user's supplemental
group vector. This plugin takes no options:
Defaults group_plugin=system_group.so
The group provider plugin API is described in detail in
sudo_plugin(5).
sudoers can log events in either JSON or sudo format, this section
describes the sudo log format. Depending on sudoers configuration,
sudoers can log events via syslog(3), to a local log file, or both.
The log format is almost identical in both cases.
Accepted command log entries
Commands that sudo runs are logged using the following format
(split into multiple lines for readability):
date hostname progname: username : TTY=ttyname ; PWD=cwd ; \
USER=runasuser ; GROUP=runasgroup ; TSID=logid ; \
ENV=env_vars COMMAND=command
Where the fields are as follows:
date The date the command was run. Typically, this is in
the format “MMM, DD, HH:MM:SS”. If logging via
syslog(3), the actual date format is controlled by
the syslog daemon. If logging to a file and the
log_year option is enabled, the date will also
include the year.
hostname The name of the host sudo was run on. This field is
only present when logging via syslog(3).
progname The name of the program, usually sudo or sudoedit.
This field is only present when logging via
syslog(3).
username The login name of the user who ran sudo.
ttyname The short name of the terminal (e.g., “console”,
“tty01”, or “pts/0”) sudo was run on, or “unknown” if
there was no terminal present.
cwd The current working directory that sudo was run in.
runasuser The user the command was run as.
runasgroup The group the command was run as if one was specified
on the command line.
logid An I/O log identifier that can be used to replay the
command's output. This is only present when the
log_input or log_output option is enabled.
env_vars A list of environment variables specified on the
command line, if specified.
command The actual command that was executed.
Messages are logged using the locale specified by sudoers_locale,
which defaults to the “C” locale.
Denied command log entries
If the user is not allowed to run the command, the reason for the
denial will follow the user name. Possible reasons include:
user NOT in sudoers
The user is not listed in the sudoers file.
user NOT authorized on host
The user is listed in the sudoers file but is not allowed to run
commands on the host.
command not allowed
The user is listed in the sudoers file for the host but they are
not allowed to run the specified command.
3 incorrect password attempts
The user failed to enter their password after 3 tries. The
actual number of tries will vary based on the number of failed
attempts and the value of the passwd_tries option.
a password is required
The -n option was specified but a password was required.
sorry, you are not allowed to set the following environment
variables
The user specified environment variables on the command line that
were not allowed by sudoers.
Error log entries
If an error occurs, sudoers will log a message and, in most cases,
send a message to the administrator via email. Possible errors
include:
parse error in /etc/sudoers near line N
sudoers encountered an error when parsing the specified file. In
some cases, the actual error may be one line above or below the
line number listed, depending on the type of error.
problem with defaults entries
The sudoers file contains one or more unknown Defaults settings.
This does not prevent sudo from running, but the sudoers file
should be checked using visudo.
timestamp owner (username): No such user
The time stamp directory owner, as specified by the
timestampowner setting, could not be found in the password
database.
unable to open/read /etc/sudoers
The sudoers file could not be opened for reading. This can
happen when the sudoers file is located on a remote file system
that maps user-ID 0 to a different value. Normally, sudoers
tries to open the sudoers file using group permissions to avoid
this problem. Consider either changing the ownership of
/etc/sudoers or adding an argument like “sudoers_uid=N” (where
‘N’ is the user-ID that owns the sudoers file) to the end of the
sudoers Plugin line in the sudo.conf(5) file.
unable to stat /etc/sudoers
The /etc/sudoers file is missing.
/etc/sudoers is not a regular file
The /etc/sudoers file exists but is not a regular file or
symbolic link.
/etc/sudoers is owned by uid N, should be 0
The sudoers file has the wrong owner. If you wish to change the
sudoers file owner, please add “sudoers_uid=N” (where ‘N’ is the
user-ID that owns the sudoers file) to the sudoers Plugin line in
the sudo.conf(5) file.
/etc/sudoers is world writable
The permissions on the sudoers file allow all users to write to
it. The sudoers file must not be world-writable, the default
file mode is 0440 (readable by owner and group, writable by
none). The default mode may be changed via the “sudoers_mode”
option to the sudoers Plugin line in the sudo.conf(5) file.
/etc/sudoers is owned by gid N, should be 1
The sudoers file has the wrong group ownership. If you wish to
change the sudoers file group ownership, please add
“sudoers_gid=N” (where ‘N’ is the group-ID that owns the sudoers
file) to the sudoers Plugin line in the sudo.conf(5) file.
unable to open /run/sudo/ts/username
sudoers was unable to read or create the user's time stamp file.
This can happen when timestampowner is set to a user other than
root and the mode on /run/sudo is not searchable by group or
other. The default mode for /run/sudo is 0711.
unable to write to /run/sudo/ts/username
sudoers was unable to write to the user's time stamp file.
/run/sudo/ts is owned by uid X, should be Y
The time stamp directory is owned by a user other than
timestampowner. This can occur when the value of timestampowner
has been changed. sudoers will ignore the time stamp directory
until the owner is corrected.
/run/sudo/ts is group writable
The time stamp directory is group-writable; it should be writable
only by timestampowner. The default mode for the time stamp
directory is 0700. sudoers will ignore the time stamp directory
until the mode is corrected.
Notes on logging via syslog
By default, sudoers logs messages via syslog(3). The date,
hostname, and progname fields are added by the system's syslog()
function, not sudoers itself. As such, they may vary in format on
different systems.
The maximum size of syslog messages varies from system to system.
The syslog_maxlen setting can be used to change the maximum syslog
message size from the default value of 980 bytes. For more
information, see the description of syslog_maxlen.
Notes on logging to a file
If the logfile option is set, sudoers will log to a local file,
such as /var/log/sudo. When logging to a file, sudoers uses a
format similar to syslog(3), with a few important differences:
1. The progname and hostname fields are not present.
2. If the log_year option is enabled, the date will also include
the year.
3. Lines that are longer than loglinelen characters (80 by
default) are word-wrapped and continued on the next line with
a four character indent. This makes entries easier to read
for a human being, but makes it more difficult to use grep(1)
on the log files. If the loglinelen option is set to 0 (or
negated with a ‘!’), word wrap will be disabled.
When I/O logging is enabled, sudo will run the command in a pseudo-
terminal and log all user input and/or output, depending on which
options are enabled. I/O can be logged either to the local machine
or to a remote log server. For local logs, I/O is logged to the
directory specified by the iolog_dir option (/var/log/sudo-io by
default) using a unique session ID that is included in the sudo log
line, prefixed with “TSID=”. The iolog_file option may be used to
control the format of the session ID. For remote logs, the
log_servers setting is used to specify one or more log servers
running sudo_logsrvd or another server that implements the protocol
described by sudo_logsrv.proto(5).
For both local and remote I/O logs, each log is stored in a
separate directory that contains the following files:
log A text file containing information about the command.
The first line consists of the following colon-delimited
fields: the time the command was run, the name of the
user who ran sudo, the name of the target user, the name
of the target group (optional), the terminal that sudo
was run from, and the number of lines and columns of the
terminal. The second and third lines contain the working
directory the command was run from and the path name of
the command itself (with arguments if present).
log.json A JSON-formatted file containing information about the
command. This is similar to the log file but contains
additional information and is easily extensible. The
log.json file will be used by sudoreplay(8) in preference
to the log file if it exists. The file may contain the
following elements:
timestamp
A JSON object containing time the command was
run. It consists of two values, seconds and
nanoseconds.
columns The number of columns of the terminal the
command ran on, or zero if no terminal was
present.
command The fully-qualified path of the command that
was run.
lines The number of lines of the terminal the command
ran on, or zero if no terminal was present.
runargv A JSON array representing the command's
argument vector as passed to the execve(2)
system call.
runenv A JSON array representing the command's
environment as passed to the execve(2) system
call.
rungid The group ID the command ran as. This element
is only present when the user specifies a group
on the command line.
rungroup The name of the group the command ran as. This
element is only present when the user specifies
a group on the command line.
runuid The user ID the command ran as.
runuser The name of the user the command ran as.
submitcwd
The current working directory at the time sudo
was run.
submithost
The name of the host the command was run on.
submituser
The name of the user who ran the command via
sudo.
ttyname The path name of the terminal the user invoked
sudo from. If the command was run in a pseudo-
terminal, ttyname will be different from the
terminal the command actually ran in.
timing Timing information used to replay the session. Each line
consists of the I/O log entry type and amount of time
since the last entry, followed by type-specific data.
The I/O log entry types and their corresponding type-
specific data are:
0 standard input, number of bytes in the entry
1 standard output, number of bytes in the entry
2 standard error, number of bytes in the entry
3 terminal input, number of bytes in the entry
4 terminal output, number of bytes in the entry
5 window change, new number lines and columns
6 bug compatibility for sudo 1.8.7 terminal output
7 command suspend or resume, signal received
ttyin Raw input from the user's terminal, exactly as it was
received. No post-processing is performed. For manual
viewing, you may wish to convert carriage return
characters in the log to line feeds. For example:
‘gunzip -c ttyin | tr "\r" "\n"’
stdin The standard input when no terminal is present, or input
redirected from a pipe or file.
ttyout Output from the pseudo-terminal (what the command writes
to the screen). Note that terminal-specific post-
processing is performed before the data is logged. This
means that, for example, line feeds are usually converted
to line feed/carriage return pairs and tabs may be
expanded to spaces.
stdout The standard output when no terminal is present, or
output redirected to a pipe or file.
stderr The standard error redirected to a pipe or file.
All files other than log are compressed in gzip format unless the
compress_io flag has been disabled. Due to buffering, it is not
normally possible to display the I/O logs in real-time as the
program is executing. The I/O log data will not be complete until
the program run by sudo has exited or has been terminated by a
signal. The iolog_flush flag can be used to disable buffering, in
which case I/O log data is written to disk as soon as it is
available. The output portion of an I/O log file can be viewed
with the sudoreplay(8) utility, which can also be used to list or
search the available logs.
Note that user input may contain sensitive information such as
passwords (even if they are not echoed to the screen), which will
be stored in the log file unencrypted. In most cases, logging the
command output via log_output or LOG_OUTPUT is all that is
required.
Since each session's I/O logs are stored in a separate directory,
traditional log rotation utilities cannot be used to limit the
number of I/O logs. The simplest way to limit the number of I/O is
by setting the maxseq option to the maximum number of logs you wish
to store. Once the I/O log sequence number reaches maxseq, it will
be reset to zero and sudoers will truncate and re-use any existing
I/O logs.
/etc/sudo.conf Sudo front end configuration
/etc/sudoers List of who can run what
/etc/group Local groups file
/etc/netgroup List of network groups
/var/log/sudo-io I/O log files
/run/sudo/ts Directory containing time stamps for the
sudoers security policy
/var/db/sudo/lectured Directory containing lecture status files
for the sudoers security policy
/etc/environment Initial environment for -i mode on AIX
and Linux systems
Below are example sudoers file entries. Admittedly, some of these
are a bit contrived. First, we allow a few environment variables
to pass and then define our aliases:
# Run X applications through sudo; HOME is used to find the
# .Xauthority file. Note that other programs use HOME to find
# configuration files and this may lead to privilege escalation!
Defaults env_keep += "DISPLAY HOME"
# User alias specification
User_Alias FULLTIMERS = millert, mikef, dowdy
User_Alias PARTTIMERS = bostley, jwfox, crawl
User_Alias WEBADMIN = will, wendy, wim
# Runas alias specification
Runas_Alias OP = root, operator
Runas_Alias DB = oracle, sybase
Runas_Alias ADMINGRP = adm, oper
# Host alias specification
Host_Alias SPARC = bigtime, eclipse, moet, anchor :\
SGI = grolsch, dandelion, black :\
ALPHA = widget, thalamus, foobar :\
HPPA = boa, nag, python
Host_Alias CUNETS = 128.138.0.0/255.255.0.0
Host_Alias CSNETS = 128.138.243.0, 128.138.204.0/24, 128.138.242.0
Host_Alias SERVERS = primary, mail, www, ns
Host_Alias CDROM = orion, perseus, hercules
# Cmnd alias specification
Cmnd_Alias DUMPS = /usr/bin/mt, /usr/sbin/dump, /usr/sbin/rdump,\
/usr/sbin/restore, /usr/sbin/rrestore,\
sha224:0GomF8mNN3wlDt1HD9XldjJ3SNgpFdbjO1+NsQ== \
/home/operator/bin/start_backups
Cmnd_Alias KILL = /usr/bin/kill
Cmnd_Alias PRINTING = /usr/sbin/lpc, /usr/bin/lprm
Cmnd_Alias SHUTDOWN = /usr/sbin/shutdown
Cmnd_Alias HALT = /usr/sbin/halt
Cmnd_Alias REBOOT = /usr/sbin/reboot
Cmnd_Alias SHELLS = /usr/bin/sh, /usr/bin/csh, /usr/bin/ksh,\
/usr/local/bin/tcsh, /usr/bin/rsh,\
/usr/local/bin/zsh
Cmnd_Alias SU = /usr/bin/su
Cmnd_Alias PAGERS = /usr/bin/more, /usr/bin/pg, /usr/bin/less
Here we override some of the compiled in default values. We want
sudo to log via syslog(3) using the auth facility in all cases and
for commands to be run with the target user's home directory as the
working directory. We don't want to subject the full time staff to
the sudo lecture and we want to allow them to run commands in a
chroot(2) “sandbox” via the -R option. User millert need not
provide a password and we don't want to reset the LOGNAME or USER
environment variables when running commands as root. Additionally,
on the machines in the SERVERS Host_Alias, we keep an additional
local log file and make sure we log the year in each log line since
the log entries will be kept around for several years. Lastly, we
disable shell escapes for the commands in the PAGERS Cmnd_Alias
(/usr/bin/more, /usr/bin/pg and /usr/bin/less). Note that this
will not effectively constrain users with sudo ALL privileges.
# Override built-in defaults
Defaults syslog=auth,runcwd=~
Defaults>root !set_logname
Defaults:FULLTIMERS !lecture,runchroot=*
Defaults:millert !authenticate
Defaults@SERVERS log_year, logfile=/var/log/sudo.log
Defaults!PAGERS noexec
The User specification is the part that actually determines who may
run what.
root ALL = (ALL) ALL
%wheel ALL = (ALL) ALL
We let root and any user in group wheel run any command on any host
as any user.
FULLTIMERS ALL = NOPASSWD: ALL
Full time sysadmins (millert, mikef, and dowdy) may run any command
on any host without authenticating themselves.
PARTTIMERS ALL = ALL
Part time sysadmins bostley, jwfox, and crawl) may run any command
on any host but they must authenticate themselves first (since the
entry lacks the NOPASSWD tag).
jack CSNETS = ALL
The user jack may run any command on the machines in the CSNETS
alias (the networks 128.138.243.0, 128.138.204.0, and
128.138.242.0). Of those networks, only 128.138.204.0 has an
explicit netmask (in CIDR notation) indicating it is a class C
network. For the other networks in CSNETS, the local machine's
netmask will be used during matching.
lisa CUNETS = ALL
The user lisa may run any command on any host in the CUNETS alias
(the class B network 128.138.0.0).
operator ALL = DUMPS, KILL, SHUTDOWN, HALT, REBOOT, PRINTING,\
sudoedit /etc/printcap, /usr/oper/bin/
The operator user may run commands limited to simple maintenance.
Here, those are commands related to backups, killing processes, the
printing system, shutting down the system, and any commands in the
directory /usr/oper/bin/. Note that one command in the DUMPS
Cmnd_Alias includes a sha224 digest,
/home/operator/bin/start_backups. This is because the directory
containing the script is writable by the operator user. If the
script is modified (resulting in a digest mismatch) it will no
longer be possible to run it via sudo.
joe ALL = /usr/bin/su operator
The user joe may only su(1) to operator.
pete HPPA = /usr/bin/passwd [A-Za-z]*, !/usr/bin/passwd *root*
%opers ALL = (: ADMINGRP) /usr/sbin/
Users in the opers group may run commands in /usr/sbin/ as
themselves with any group in the ADMINGRP Runas_Alias (the adm and
oper groups).
The user pete is allowed to change anyone's password except for
root on the HPPA machines. Because command line arguments are
matched as a single, concatenated string, the ‘*’ wildcard will
match multiple words. This example assumes that passwd(1) does not
take multiple user names on the command line. Note that on GNU
systems, options to passwd(1) may be specified after the user
argument. As a result, this rule will also allow:
passwd username --expire
which may not be desirable.
bob SPARC = (OP) ALL : SGI = (OP) ALL
The user bob may run anything on the SPARC and SGI machines as any
user listed in the OP Runas_Alias (root and operator.)
jim +biglab = ALL
The user jim may run any command on machines in the biglab
netgroup. sudo knows that “biglab” is a netgroup due to the ‘+’
prefix.
+secretaries ALL = PRINTING, /usr/bin/adduser, /usr/bin/rmuser
Users in the secretaries netgroup need to help manage the printers
as well as add and remove users, so they are allowed to run those
commands on all machines.
fred ALL = (DB) NOPASSWD: ALL
The user fred can run commands as any user in the DB Runas_Alias
(oracle or sybase) without giving a password.
john ALPHA = /usr/bin/su [!-]*, !/usr/bin/su *root*
On the ALPHA machines, user john may su to anyone except root but
he is not allowed to specify any options to the su(1) command.
jen ALL, !SERVERS = ALL
The user jen may run any command on any machine except for those in
the SERVERS Host_Alias (primary, mail, www and ns).
jill SERVERS = /usr/bin/, !SU, !SHELLS
For any machine in the SERVERS Host_Alias, jill may run any
commands in the directory /usr/bin/ except for those commands
belonging to the SU and SHELLS Cmnd_Aliases. While not
specifically mentioned in the rule, the commands in the PAGERS
Cmnd_Alias all reside in /usr/bin and have the noexec option set.
steve CSNETS = (operator) /usr/local/op_commands/
The user steve may run any command in the directory
/usr/local/op_commands/ but only as user operator.
matt valkyrie = KILL
On his personal workstation, valkyrie, matt needs to be able to
kill hung processes.
WEBADMIN www = (www) ALL, (root) /usr/bin/su www
On the host www, any user in the WEBADMIN User_Alias (will, wendy,
and wim), may run any command as user www (which owns the web
pages) or simply su(1) to www.
ALL CDROM = NOPASSWD: /sbin/umount /CDROM,\
/sbin/mount -o nosuid\,nodev /dev/cd0a /CDROM
Any user may mount or unmount a CD-ROM on the machines in the CDROM
Host_Alias (orion, perseus, hercules) without entering a password.
This is a bit tedious for users to type, so it is a prime candidate
for encapsulating in a shell script.
Limitations of the ‘!’ operator
It is generally not effective to “subtract” commands from ALL using
the ‘!’ operator. A user can trivially circumvent this by copying
the desired command to a different name and then executing that.
For example:
bill ALL = ALL, !SU, !SHELLS
Doesn't really prevent bill from running the commands listed in SU
or SHELLS since he can simply copy those commands to a different
name, or use a shell escape from an editor or other program.
Therefore, these kind of restrictions should be considered advisory
at best (and reinforced by policy).
In general, if a user has sudo ALL there is nothing to prevent them
from creating their own program that gives them a root shell (or
making their own copy of a shell) regardless of any ‘!’ elements in
the user specification.
Security implications of fast_glob
If the fast_glob option is in use, it is not possible to reliably
negate commands where the path name includes globbing (aka
wildcard) characters. This is because the C library's fnmatch(3)
function cannot resolve relative paths. While this is typically
only an inconvenience for rules that grant privileges, it can
result in a security issue for rules that subtract or revoke
privileges.
For example, given the following sudoers file entry:
john ALL = /usr/bin/passwd [a-zA-Z0-9]*, /usr/bin/chsh [a-zA-Z0-9]*,\
/usr/bin/chfn [a-zA-Z0-9]*, !/usr/bin/* root
User john can still run /usr/bin/passwd root if fast_glob is
enabled by changing to /usr/bin and running ./passwd root instead.
Preventing shell escapes
Once sudo executes a program, that program is free to do whatever
it pleases, including run other programs. This can be a security
issue since it is not uncommon for a program to allow shell
escapes, which lets a user bypass sudo's access control and
logging. Common programs that permit shell escapes include shells
(obviously), editors, paginators, mail and terminal programs.
There are two basic approaches to this problem:
restrict Avoid giving users access to commands that allow the user
to run arbitrary commands. Many editors have a
restricted mode where shell escapes are disabled, though
sudoedit is a better solution to running editors via
sudo. Due to the large number of programs that offer
shell escapes, restricting users to the set of programs
that do not is often unworkable.
noexec Many systems that support shared libraries have the
ability to override default library functions by pointing
an environment variable (usually LD_PRELOAD) to an
alternate shared library. On such systems, sudo's noexec
functionality can be used to prevent a program run by
sudo from executing any other programs. Note, however,
that this applies only to dynamically-linked executables.
Statically-linked executables and executables running
under binary emulation are not affected.
The noexec feature is known to work on SunOS, Solaris,
*BSD, Linux, IRIX, Tru64 UNIX, macOS, HP-UX 11.x and AIX
5.3 and above. It should be supported on most operating
systems that support the LD_PRELOAD environment variable.
Check your operating system's manual pages for the
dynamic linker (usually ld.so, ld.so.1, dyld, dld.sl,
rld, or loader) to see if LD_PRELOAD is supported.
On Solaris 10 and higher, noexec uses Solaris privileges
instead of the LD_PRELOAD environment variable.
To enable noexec for a command, use the NOEXEC tag as
documented in the User Specification section above. Here
is that example again:
aaron shanty = NOEXEC: /usr/bin/more, /usr/bin/vi
This allows user aaron to run /usr/bin/more and
/usr/bin/vi with noexec enabled. This will prevent those
two commands from executing other commands (such as a
shell). If you are unsure whether or not your system is
capable of supporting noexec you can always just try it
out and check whether shell escapes work when noexec is
enabled.
Note that restricting shell escapes is not a panacea. Programs
running as root are still capable of many potentially hazardous
operations (such as changing or overwriting files) that could lead
to unintended privilege escalation. In the specific case of an
editor, a safer approach is to give the user permission to run
sudoedit (see below).
Secure editing
The sudoers plugin includes sudoedit support which allows users to
securely edit files with the editor of their choice. As sudoedit
is a built-in command, it must be specified in the sudoers file
without a leading path. However, it may take command line
arguments just as a normal command does. Wildcards used in
sudoedit command line arguments are expected to be path names, so a
forward slash (‘/’) will not be matched by a wildcard.
Unlike other sudo commands, the editor is run with the permissions
of the invoking user and with the environment unmodified. More
information may be found in the description of the -e option in
sudo(8).
For example, to allow user operator to edit the “message of the
day” file:
operator sudoedit /etc/motd
The operator user then runs sudoedit as follows:
$ sudoedit /etc/motd
The editor will run as the operator user, not root, on a temporary
copy of /etc/motd. After the file has been edited, /etc/motd will
be updated with the contents of the temporary copy.
Users should never be granted sudoedit permission to edit a file
that resides in a directory the user has write access to, either
directly or via a wildcard. If the user has write access to the
directory it is possible to replace the legitimate file with a link
to another file, allowing the editing of arbitrary files. To
prevent this, starting with version 1.8.16, symbolic links will not
be followed in writable directories and sudoedit will refuse to
edit a file located in a writable directory unless the
sudoedit_checkdir option has been disabled or the invoking user is
root. Additionally, in version 1.8.15 and higher, sudoedit will
refuse to open a symbolic link unless either the sudoedit_follow
option is enabled or the sudoedit command is prefixed with the
FOLLOW tag in the sudoers file.
Time stamp file checks
sudoers will check the ownership of its time stamp directory
(/run/sudo/ts by default) and ignore the directory's contents if it
is not owned by root or if it is writable by a user other than
root. Older versions of sudo stored time stamp files in /tmp; this
is no longer recommended as it may be possible for a user to create
the time stamp themselves on systems that allow unprivileged users
to change the ownership of files they create.
While the time stamp directory should be cleared at reboot time,
not all systems contain a /run or /var/run directory. To avoid
potential problems, sudoers will ignore time stamp files that date
from before the machine booted on systems where the boot time is
available.
Some systems with graphical desktop environments allow unprivileged
users to change the system clock. Since sudoers relies on the
system clock for time stamp validation, it may be possible on such
systems for a user to run sudo for longer than timestamp_timeout by
setting the clock back. To combat this, sudoers uses a monotonic
clock (which never moves backwards) for its time stamps if the
system supports it.
sudoers will not honor time stamps set far in the future. Time
stamps with a date greater than current_time + 2 * TIMEOUT will be
ignored and sudoers will log and complain.
If the timestamp_type option is set to “tty”, the time stamp record
includes the device number of the terminal the user authenticated
with. This provides per-terminal granularity but time stamp
records may still outlive the user's session.
Unless the timestamp_type option is set to “global”, the time stamp
record also includes the session ID of the process that last
authenticated. This prevents processes in different terminal
sessions from using the same time stamp record. On systems where a
process's start time can be queried, the start time of the session
leader is recorded in the time stamp record. If no terminal is
present or the timestamp_type option is set to “ppid”, the start
time of the parent process is used instead. In most cases this
will prevent a time stamp record from being re-used without the
user entering a password when logging out and back in again.
Versions 1.8.4 and higher of the sudoers plugin support a flexible
debugging framework that can help track down what the plugin is
doing internally if there is a problem. This can be configured in
the sudo.conf(5) file.
The sudoers plugin uses the same debug flag format as the sudo
front-end: subsystem@priority.
The priorities used by sudoers, in order of decreasing severity,
are: crit, err, warn, notice, diag, info, trace and debug. Each
priority, when specified, also includes all priorities higher than
it. For example, a priority of notice would include debug messages
logged at notice and higher.
The following subsystems are used by the sudoers plugin:
alias User_Alias, Runas_Alias, Host_Alias and Cmnd_Alias
processing
all matches every subsystem
audit BSM and Linux audit code
auth user authentication
defaults sudoers file Defaults settings
env environment handling
ldap LDAP-based sudoers
logging logging support
match matching of users, groups, hosts and netgroups in the
sudoers file
netif network interface handling
nss network service switch handling in sudoers
parser sudoers file parsing
perms permission setting
plugin The equivalent of main for the plugin.
pty pseudo-terminal related code
rbtree redblack tree internals
sssd SSSD-based sudoers
util utility functions
For example:
Debug sudo /var/log/sudo_debug match@info,nss@info
For more information, see the sudo.conf(5) manual.
ssh(1), su(1), fnmatch(3), glob(3), mktemp(3), strftime(3),
sudo.conf(5), sudo_plugin(5), sudoers.ldap(5),
sudoers_timestamp(5), sudo(8), visudo(8)
Many people have worked on sudo over the years; this version
consists of code written primarily by:
Todd C. Miller
See the CONTRIBUTORS file in the sudo distribution
(https://www.sudo.ws/contributors.html) for an exhaustive list of
people who have contributed to sudo.
The sudoers file should always be edited by the visudo utility
which locks the file and checks for syntax errors. If sudoers
contains syntax errors, sudo may refuse to run, which is a serious
problem if sudo is your only method of obtaining superuser
privileges. Recent versions of sudoers will attempt to recover
after a syntax error by ignoring the rest of the line after
encountering an error. Older versions of sudo will not run if
sudoers contains a syntax error.
When using netgroups of machines (as opposed to users), if you
store fully qualified host name in the netgroup (as is usually the
case), you either need to have the machine's host name be fully
qualified as returned by the hostname command or use the fqdn
option in sudoers.
If you feel you have found a bug in sudo, please submit a bug
report at https://bugzilla.sudo.ws/
Limited free support is available via the sudo-users mailing list,
see https://www.sudo.ws/mailman/listinfo/sudo-users to subscribe or
search the archives.
sudo is provided “AS IS” and any express or implied warranties,
including, but not limited to, the implied warranties of
merchantability and fitness for a particular purpose are
disclaimed. See the LICENSE file distributed with sudo or
https://www.sudo.ws/license.html for complete details.
This page is part of the sudo (execute a command as another user)
project. Information about the project can be found at
https://www.sudo.ws/. If you have a bug report for this manual
page, see ⟨https://bugzilla.sudo.ws/⟩. This page was obtained from
the project's upstream Git repository
⟨https://github.com/sudo-project/sudo⟩ on 2020-12-18. (At that
time, the date of the most recent commit that was found in the
repository was 2020-12-15.) If you discover any rendering problems
in this HTML version of the page, or you believe there is a better
or more up-to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not part
of the original manual page), send a mail to man-pages@man7.org
Sudo 1.9.4p1 December 11, 2020 Sudo 1.9.4p1
Pages that refer to this page: proc(5)
|
HTML rendering created 2020-12-21 by Michael Kerrisk, author of The Linux Programming Interface, maintainer of the Linux man-pages project. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
|