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NAME | SYNOPSIS | DESCRIPTION | OPTIONS | CONFIGURATION FILE | TCP_WRAPPERS SUPPORT | FILES | SEE ALSO | AUTHOR | COLOPHON |
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rpc.mountd(8) System Manager's Manual rpc.mountd(8)
rpc.mountd - NFS mount daemon
/usr/sbin/rpc.mountd [options]
The rpc.mountd daemon implements the server side of the NFS MOUNT
protocol, an NFS side protocol used by NFS version 2 [RFC1094]
and NFS version 3 [RFC1813].
An NFS server maintains a table of local physical file systems
that are accessible to NFS clients. Each file system in this
table is referred to as an exported file system, or export, for
short.
Each file system in the export table has an access control list.
rpc.mountd uses these access control lists to determine whether
an NFS client is permitted to access a given file system. For
details on how to manage your NFS server's export table, see the
exports(5) and exportfs(8) man pages.
Mounting exported NFS File Systems
The NFS MOUNT protocol has several procedures. The most
important of these are MNT (mount an export) and UMNT (unmount an
export).
A MNT request has two arguments: an explicit argument that
contains the pathname of the root directory of the export to be
mounted, and an implicit argument that is the sender's IP
address.
When receiving a MNT request from an NFS client, rpc.mountd
checks both the pathname and the sender's IP address against its
export table. If the sender is permitted to access the requested
export, rpc.mountd returns an NFS file handle for the export's
root directory to the client. The client can then use the root
file handle and NFS LOOKUP requests to navigate the directory
structure of the export.
The rmtab File
The rpc.mountd daemon registers every successful MNT request by
adding an entry to the /var/lib/nfs/rmtab file. When receivng a
UMNT request from an NFS client, rpc.mountd simply removes the
matching entry from /var/lib/nfs/rmtab, as long as the access
control list for that export allows that sender to access the
export.
Clients can discover the list of file systems an NFS server is
currently exporting, or the list of other clients that have
mounted its exports, by using the showmount(8) command.
showmount(8) uses other procedures in the NFS MOUNT protocol to
report information about the server's exported file systems.
Note, however, that there is little to guarantee that the
contents of /var/lib/nfs/rmtab are accurate. A client may
continue accessing an export even after invoking UMNT. If the
client reboots without sending a UMNT request, stale entries
remain for that client in /var/lib/nfs/rmtab.
-d kind or --debug kind
Turn on debugging. Valid kinds are: all, auth, call,
general and parse.
-F or --foreground
Run in foreground (do not daemonize)
-h or --help
Display usage message.
-o num or --descriptors num
Set the limit of the number of open file descriptors to
num. The default is to leave the limit unchanged.
-N mountd-version or --no-nfs-version mountd-version
This option can be used to request that rpc.mountd do not
offer certain versions of NFS. The current version of
rpc.mountd can support both NFS version 2, 3 and 4. If the
either one of these version should not be offered,
rpc.mountd must be invoked with the option --no-nfs-
version <vers> .
-n or --no-tcp
Don't advertise TCP for mount.
-p num or -P num or --port num
Specifies the port number used for RPC listener sockets.
If this option is not specified, rpc.mountd will try to
consult /etc/services, if gets port succeed, set the same
port for all listener socket, otherwise chooses a random
ephemeral port for each listener socket.
This option can be used to fix the port value of
rpc.mountd's listeners when NFS MOUNT requests must
traverse a firewall between clients and servers.
-H prog or --ha-callout prog
Specify a high availability callout program. This program
receives callouts for all MOUNT and UNMOUNT requests.
This allows rpc.mountd to be used in a High Availability
NFS (HA-NFS) environment.
The callout program is run with 4 arguments. The first is
mount or unmount depending on the reason for the callout.
The second will be the name of the client performing the
mount. The third will be the path that the client is
mounting. The last is the number of concurrent mounts
that we believe the client has of that path.
This callout is not needed with 2.6 and later kernels.
Instead, mount the nfsd filesystem on /proc/fs/nfsd.
-s, --state-directory-path directory
Specify a directory in which to place state information
(etab and rmtab). If this option is not specified the
default of /var/lib/nfs is used.
-r, --reverse-lookup
rpc.mountd tracks IP addresses in the rmtab file. When a
DUMP request is made (by someone running showmount -a, for
instance), it returns IP addresses instead of hostnames by
default. This option causes rpc.mountd to perform a
reverse lookup on each IP address and return that hostname
instead. Enabling this can have a substantial negative
effect on performance in some situations.
-t N or --num-threads=N or --num-threads N
This option specifies the number of worker threads that
rpc.mountd spawns. The default is 1 thread, which is
probably enough. More threads are usually only needed for
NFS servers which need to handle mount storms of hundreds
of NFS mounts in a few seconds, or when your DNS server is
slow or unreliable.
-u or --no-udp
Don't advertise UDP for mounting
-V version or --nfs-version version
This option can be used to request that rpc.mountd offer
certain versions of NFS. The current version of rpc.mountd
can support both NFS version 2 and the newer version 3.
-v or --version
Print the version of rpc.mountd and exit.
-g or --manage-gids
Accept requests from the kernel to map user id numbers
into lists of group id numbers for use in access control.
An NFS request will normally (except when using Kerberos
or other cryptographic authentication) contains a user-id
and a list of group-ids. Due to a limitation in the NFS
protocol, at most 16 groups ids can be listed. If you use
the -g flag, then the list of group ids received from the
client will be replaced by a list of group ids determined
by an appropriate lookup on the server. Note that the
'primary' group id is not affected so a newgroup command
on the client will still be effective. This function
requires a Linux Kernel with version at least 2.6.21.
Many of the options that can be set on the command line can also
be controlled through values set in the [mountd] or, in some
cases, the [nfsd] sections of the /etc/nfs.conf configuration
file. Values recognized in the [mountd] section include manage-
gids, descriptors, port, threads, reverse-lookup, and state-
directory-path, ha-callout which each have the same effect as the
option with the same name.
The values recognized in the [nfsd] section include TCP, UDP,
vers2, vers3, and vers4 which each have same same meaning as
given by rpc.nfsd(8).
You can protect your rpc.mountd listeners using the tcp_wrapper
library or iptables(8).
Note that the tcp_wrapper library supports only IPv4 networking.
Add the hostnames of NFS peers that are allowed to access
rpc.mountd to /etc/hosts.allow. Use the daemon name mountd even
if the rpc.mountd binary has a different name.
Hostnames used in either access file will be ignored when they
can not be resolved into IP addresses. For further information
see the tcpd(8) and hosts_access(5) man pages.
IPv6 and TI-RPC support
TI-RPC is a pre-requisite for supporting NFS on IPv6. If TI-RPC
support is built into rpc.mountd, it attempts to start listeners
on network transports marked 'visible' in /etc/netconfig. As
long as at least one network transport listener starts
successfully, rpc.mountd will operate.
/etc/exports
input file for exportfs, listing exports, export options,
and access control lists
/var/lib/nfs/rmtab
table of clients accessing server's exports
exportfs(8), exports(5), showmount(8), rpc.nfsd(8),
rpc.rquotad(8), nfs(5), nfs.conf(5), tcpd(8), hosts_access(5),
iptables(8), netconfig(5)
RFC 1094 - "NFS: Network File System Protocol Specification"
RFC 1813 - "NFS Version 3 Protocol Specification"
Olaf Kirch, H. J. Lu, G. Allan Morris III, and a host of others.
This page is part of the nfs-utils (NFS utilities) project.
Information about the project can be found at
⟨http://linux-nfs.org/wiki/index.php/Main_Page⟩. If you have a
bug report for this manual page, see
⟨http://linux-nfs.org/wiki/index.php/Main_Page⟩. This page was
obtained from the project's upstream Git repository
⟨http://git.linux-nfs.org/?p=steved/nfs-utils.git;a=summary⟩ on
2020-12-18. (At that time, the date of the most recent commit
that was found in the repository was 2020-12-16.) 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
31 Dec 2009 rpc.mountd(8)
Pages that refer to this page: exports(5), nfs.conf(5), nfsd(7), exportfs(8), mount(8), nfsd(8), showmount(8)
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