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NAME | SYNOPSIS | DESCRIPTION | ARGUMENTS | OPTIONS | EXAMPLE | SECURITY NOTICE | ISSUE FILES | FILES | BUGS | DIAGNOSTICS | AUTHORS | AVAILABILITY | COLOPHON |
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AGETTY(8) System Administration AGETTY(8)
agetty - alternative Linux getty
agetty [options] port [baud_rate...] [term]
agetty opens a tty port, prompts for a login name and invokes the
/bin/login command. It is normally invoked by init(8).
agetty has several non-standard features that are useful for
hardwired and for dial-in lines:
• Adapts the tty settings to parity bits and to erase, kill,
end-of-line and uppercase characters when it reads a login
name. The program can handle 7-bit characters with even,
odd, none or space parity, and 8-bit characters with no
parity. The following special characters are recognized:
Control-U (kill); DEL and backspace (erase); carriage
return and line feed (end of line). See also the
--erase-chars and --kill-chars options.
• Optionally deduces the baud rate from the CONNECT messages
produced by Hayes(tm)-compatible modems.
• Optionally does not hang up when it is given an already
opened line (useful for call-back applications).
• Optionally does not display the contents of the /etc/issue
file.
• Optionally displays an alternative issue files or
directories instead of /etc/issue or /etc/issue.d.
• Optionally does not ask for a login name.
• Optionally invokes a non-standard login program instead of
/bin/login.
• Optionally turns on hardware flow control.
• Optionally forces the line to be local with no need for
carrier detect.
This program does not use the /etc/gettydefs (System V) or
/etc/gettytab (SunOS 4) files.
port A path name relative to the /dev directory. If a "-" is
specified, agetty assumes that its standard input is
already connected to a tty port and that a connection to a
remote user has already been established.
Under System V, a "-" port argument should be preceded by
a "--".
baud_rate,...
A comma-separated list of one or more baud rates. Each
time agetty receives a BREAK character it advances through
the list, which is treated as if it were circular.
Baud rates should be specified in descending order, so
that the null character (Ctrl-@) can also be used for
baud-rate switching.
This argument is optional and unnecessary for virtual
terminals.
The default for serial terminals is keep the current baud
rate (see --keep-baud) and if unsuccessful then default to
'9600'.
term The value to be used for the TERM environment variable.
This overrides whatever init(1) may have set, and is
inherited by login and the shell.
The default is 'vt100', or 'linux' for Linux on a virtual
terminal, or 'hurd' for GNU Hurd on a virtual terminal.
-8, --8bits
Assume that the tty is 8-bit clean, hence disable parity
detection.
-a, --autologin username
Automatically log in the specified user without asking for
a username or password. Using this option causes an -f
username option and argument to be added to the /bin/login
command line. See --login-options, which can be used to
modify this option's behavior.
Note that --autologin may affect the way in which getty
initializes the serial line, because on auto-login agetty
does not read from the line and it has no opportunity
optimize the line setting.
-c, --noreset
Do not reset terminal cflags (control modes). See
termios(3) for more details.
-E, --remote
Typically the login(1) command is given a remote hostname
when called by something such as telnetd(8). This option
allows agetty to pass what it is using for a hostname to
login(1) for use in utmp(5). See --host, login(1), and
utmp(5).
If the --host fakehost option is given, then an -h
fakehost option and argument are added to the /bin/login
command line.
If the --nohostname option is given, then an -H option is
added to the /bin/login command line.
See --login-options.
-f, --issue-file path
Specifies a ":" delimited list of files and directories to
be displayed instead of /etc/issue (or other). All
specified files and directories are displayed, missing or
empty files are silently ignored. If the specified path
is a directory then display all files with .issue file
extension in version-sort order from the directory. This
allows custom messages to be displayed on different
terminals. The --noissue option will override this
option.
--show-issue
Display the current issue file (or other) on the current
terminal and exit. Use this option to review the current
setting, it is not designed for any other purpose. Note
that output may use some default or incomplete information
as proper output depends on terminal and agetty command
line.
-h, --flow-control
Enable hardware (RTS/CTS) flow control. It is left up to
the application to disable software (XON/XOFF) flow
protocol where appropriate.
-H, --host fakehost
Write the specified fakehost into the utmp file.
Normally, no login host is given, since agetty is used for
local hardwired connections and consoles. However, this
option can be useful for identifying terminal
concentrators and the like.
-i, --noissue
Do not display the contents of /etc/issue (or other)
before writing the login prompt. Terminals or
communications hardware may become confused when receiving
lots of text at the wrong baud rate; dial-up scripts may
fail if the login prompt is preceded by too much text.
-I, --init-string initstring
Set an initial string to be sent to the tty or modem
before sending anything else. This may be used to
initialize a modem. Non-printable characters may be sent
by writing their octal code preceded by a backslash (\).
For example, to send a linefeed character (ASCII 10, octal
012), write \012.
-J, --noclear
Do not clear the screen before prompting for the login
name. By default the screen is cleared.
-l, --login-program login_program
Invoke the specified login_program instead of /bin/login.
This allows the use of a non-standard login program. Such
a program could, for example, ask for a dial-up password
or use a different password file. See --login-options.
-L, --local-line[=mode]
Control the CLOCAL line flag. The optional mode argument
is 'auto', 'always' or 'never'. If the mode argument is
omitted, then the default is 'always'. If the
--local-line option is not given at all, then the default
is 'auto'.
always Forces the line to be a local line with no need for
carrier detect. This can be useful when you have a
locally attached terminal where the serial line
does not set the carrier-detect signal.
never Explicitly clears the CLOCAL flag from the line
setting and the carrier-detect signal is expected
on the line.
auto The agetty default. Does not modify the CLOCAL
setting and follows the setting enabled by the
kernel.
-m, --extract-baud
Try to extract the baud rate from the CONNECT status
message produced by Hayes(tm)-compatible modems. These
status messages are of the form: "<junk><speed><junk>".
agetty assumes that the modem emits its status message at
the same speed as specified with (the first) baud_rate
value on the command line.
Since the --extract-baud feature may fail on heavily-
loaded systems, you still should enable BREAK processing
by enumerating all expected baud rates on the command
line.
--list-speeds
Display supported baud rates. These are determined at
compilation time.
-n, --skip-login
Do not prompt the user for a login name. This can be used
in connection with the --login-program option to invoke a
non-standard login process such as a BBS system. Note
that with the --skip-login option, agetty gets no input
from the user who logs in and therefore will not be able
to figure out parity, character size, and newline
processing of the connection. It defaults to space
parity, 7 bit characters, and ASCII CR (13) end-of-line
character. Beware that the program that agetty starts
(usually /bin/login) is run as root.
-N, --nonewline
Do not print a newline before writing out /etc/issue.
-o, --login-options "login_options"
Options and arguments that are passed to login(1). Where
\u is replaced by the login name. For example:
--login-options '-h darkstar -- \u'
See --autologin, --login-program and --remote.
Please read the SECURITY NOTICE below before using this
option.
-p, --login-pause
Wait for any key before dropping to the login prompt. Can
be combined with --autologin to save memory by lazily
spawning shells.
-r, --chroot directory
Change root to the specified directory.
-R, --hangup
Call vhangup() to do a virtual hangup of the specified
terminal.
-s, --keep-baud
Try to keep the existing baud rate. The baud rates from
the command line are used when agetty receives a BREAK
character. If another baud rates specified then the
original baud rate is also saved to the end of the wanted
baud rates list. This can be used to return to the
original baud rate after unexpected BREAKs.
-t, --timeout timeout
Terminate if no user name could be read within timeout
seconds. Use of this option with hardwired terminal lines
is not recommended.
-U, --detect-case
Turn on support for detecting an uppercase-only terminal.
This setting will detect a login name containing only
capitals as indicating an uppercase-only terminal and turn
on some upper-to-lower case conversions. Note that this
has no support for any Unicode characters.
-w, --wait-cr
Wait for the user or the modem to send a carriage-return
or a linefeed character before sending the /etc/issue file
(or others) and the login prompt. This is useful with the
--init-string option.
--nohints
Do not print hints about Num, Caps and Scroll Locks.
--nohostname
By default the hostname will be printed. With this option
enabled, no hostname at all will be shown.
--long-hostname
By default the hostname is only printed until the first
dot. With this option enabled, the fully qualified
hostname by gethostname(3P) or (if not found) by
getaddrinfo(3) is shown.
--erase-chars string
This option specifies additional characters that should be
interpreted as a backspace ("ignore the previous
character") when the user types the login name. The
default additional ´erase´ has been ´#´, but since util-
linux 2.23 no additional erase characters are enabled by
default.
--kill-chars string
This option specifies additional characters that should be
interpreted as a kill ("ignore all previous characters")
when the user types the login name. The default
additional ´kill´ has been ´@´, but since util-linux 2.23
no additional kill characters are enabled by default.
--chdir directory
Change directory before the login.
--delay number
Sleep seconds before open tty.
--nice number
Run login with this priority.
--reload
Ask all running agetty instances to reload and update
their displayed prompts, if the user has not yet commenced
logging in. After doing so the command will exit. This
feature might be unsupported on systems without Linux
inotify(7).
--version
Display version information and exit.
--help Display help text and exit.
This section shows examples for the process field of an entry in
the /etc/inittab file. You'll have to prepend appropriate values
for the other fields. See inittab(5) for more details.
For a hardwired line or a console tty:
/sbin/agetty 9600 ttyS1
For a directly connected terminal without proper carrier-detect
wiring (try this if your terminal just sleeps instead of giving
you a password: prompt):
/sbin/agetty --local-line 9600 ttyS1 vt100
For an old-style dial-in line with a 9600/2400/1200 baud modem:
/sbin/agetty --extract-baud --timeout 60 ttyS1 9600,2400,1200
For a Hayes modem with a fixed 115200 bps interface to the
machine (the example init string turns off modem echo and result
codes, makes modem/computer DCD track modem/modem DCD, makes a
DTR drop cause a disconnection, and turns on auto-answer after 1
ring):
/sbin/agetty --wait-cr --init-string 'ATE0Q1&D2&C1S0=1 15' 115200 ttyS1
If you use the --login-program and --login-options options, be
aware that a malicious user may try to enter lognames with
embedded options, which then get passed to the used login
program. Agetty does check for a leading "-" and makes sure the
logname gets passed as one parameter (so embedded spaces will not
create yet another parameter), but depending on how the login
binary parses the command line that might not be sufficient.
Check that the used login program cannot be abused this way.
Some programs use "--" to indicate that the rest of the command
line should not be interpreted as options. Use this feature if
available by passing "--" before the username gets passed by \u.
The default issue file is /etc/issue. If the file exists, then
agetty also checks for /etc/issue.d directory. The directory is
optional extension to the default issue file and content of the
directory is printed after /etc/issue content. If the /etc/issue
does not exist, then the directory is ignored. All files with
.issue extension from the directory are printed in version-sort
order. The directory can be used to maintain 3rd-party messages
independently on the primary system /etc/issue file.
Since version 2.35 additional locations for issue file and
directory are supported. If the default /etc/issue does not
exist, then agetty checks for /run/issue and /run/issue.d,
thereafter for /usr/lib/issue and /usr/lib/issue.d. The
directory /etc is expected for host specific configuration, /run
is expected for generated stuff and /usr/lib for static
distribution maintained configuration.
The default path maybe overridden by --issue-file option. In this
case specified path has to be file or directory and all the
default issue file and directory locations are ignored.
The issue file feature can be completely disabled by --noissue
option.
It is possible to review the current issue file by agetty
--show-issue on the current terminal.
The issue files may contain certain escape codes to display the
system name, date, time et cetera. All escape codes consist of a
backslash (\) immediately followed by one of the characters
listed below.
4 or 4{interface}
Insert the IPv4 address of the specified network interface
(for example: \4{eth0}). If the interface argument is not
specified, then select the first fully configured (UP,
non-LOCALBACK, RUNNING) interface. If not any configured
interface is found, fall back to the IP address of the
machine's hostname.
6 or 6{interface}
The same as \4 but for IPv6.
b Insert the baudrate of the current line.
d Insert the current date.
e or e{name}
Translate the human-readable name to an escape sequence
and insert it (for example: \e{red}Alert text.\e{reset}).
If the name argument is not specified, then insert \033.
The currently supported names are: black, blink, blue,
bold, brown, cyan, darkgray, gray, green, halfbright,
lightblue, lightcyan, lightgray, lightgreen, lightmagenta,
lightred, magenta, red, reset, reverse, yellow and white.
All unknown names are silently ignored.
s Insert the system name (the name of the operating system).
Same as 'uname -s'. See also the \S escape code.
S or S{VARIABLE}
Insert the VARIABLE data from /etc/os-release. If this
file does not exist then fall back to /usr/lib/os-release.
If the VARIABLE argument is not specified, then use
PRETTY_NAME from the file or the system name (see \s).
This escape code can be used to keep /etc/issue
distribution and release independent. Note that
\S{ANSI_COLOR} is converted to the real terminal escape
sequence.
l Insert the name of the current tty line.
m Insert the architecture identifier of the machine. Same
as 'uname -m'.
n Insert the nodename of the machine, also known as the
hostname. Same as 'uname -n'.
o Insert the NIS domainname of the machine. Same as
'hostname -d'.
O Insert the DNS domainname of the machine.
r Insert the release number of the OS. Same as 'uname -r'.
t Insert the current time.
u Insert the number of current users logged in.
U Insert the string "1 user" or "<n> users" where <n> is the
number of current users logged in.
v Insert the version of the OS, that is, the build-date and
such.
An example. On my system, the following /etc/issue file:
This is \n.\o (\s \m \r) \t
displays as:
This is thingol.orcan.dk (Linux i386 1.1.9) 18:29:30
/var/run/utmp
the system status file.
/etc/issue
printed before the login prompt.
/etc/os-release /usr/lib/os-release
operating system identification data.
/dev/console
problem reports (if syslog(3) is not used).
/etc/inittab
init(8) configuration file for SysV-style init daemon.
The baud-rate detection feature (the --extract-baud option)
requires that agetty be scheduled soon enough after completion of
a dial-in call (within 30 ms with modems that talk at 2400 baud).
For robustness, always use the --extract-baud option in
combination with a multiple baud rate command-line argument, so
that BREAK processing is enabled.
The text in the /etc/issue file (or other) and the login prompt
are always output with 7-bit characters and space parity.
The baud-rate detection feature (the --extract-baud option)
requires that the modem emits its status message after raising
the DCD line.
Depending on how the program was configured, all diagnostics are
written to the console device or reported via the syslog(3)
facility. Error messages are produced if the port argument does
not specify a terminal device; if there is no utmp entry for the
current process (System V only); and so on.
Werner Fink ⟨werner@suse.de⟩
Karel Zak ⟨kzak@redhat.com⟩
The original agetty for serial terminals was written by W.Z.
Venema <wietse@wzv.win.tue.nl> and ported to Linux by Peter
Orbaek <poe@daimi.aau.dk>.
The agetty command is part of the util-linux package and is
available from
https://www.kernel.org/pub/linux/utils/util-linux/.
This page is part of the util-linux (a random collection of Linux
utilities) project. Information about the project can be found
at ⟨https://www.kernel.org/pub/linux/utils/util-linux/⟩. If you
have a bug report for this manual page, send it to
util-linux@vger.kernel.org. This page was obtained from the
project's upstream Git repository
⟨git://git.kernel.org/pub/scm/utils/util-linux/util-linux.git⟩ on
2020-12-18. (At that time, the date of the most recent commit
that was found in the repository was 2020-12-17.) 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
util-linux February 2016 AGETTY(8)
Pages that refer to this page: tty(4), ttyS(4), issue(5), systemd.exec(5), ttytype(5), utmp(5), systemd-getty-generator(8)
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