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+.\"@(#)rpc.mountd.8"
+.\"
+.\" Copyright (C) 1999 Olaf Kirch <okir@monad.swb.de>
+.\" Modified by Paul Clements, 2004.
+.\"
+.TH rpc.mountd 8 "31 Dec 2009"
+.SH NAME
+rpc.mountd \- NFS mount daemon
+.SH SYNOPSIS
+.BI "/usr/sbin/rpc.mountd [" options "]"
+.SH DESCRIPTION
+The
+.B 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].
+It also responds to requests from the Linux kernel to authenticate
+clients and provides details of access permissions.
+.PP
+The NFS server
+.RI ( nfsd )
+maintains a cache of authentication and authorization information which
+is used to identify the source of each request, and then what access
+permissions that source has to any local filesystem. When required
+information is not found in the cache, the server sends a request to
+.B mountd
+to fill in the missing information. Mountd uses a table of information
+stored in
+.B /var/lib/nfs/etab
+and maintained by
+.BR exportfs (8),
+possibly based on the contents of
+.BR exports (5),
+to respond to each request.
+.SS 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).
+.PP
+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.
+.PP
+When receiving a MNT request from an NFS client,
+.B 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,
+.B 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.
+.SS The rmtab File
+The
+.B rpc.mountd
+daemon registers every successful MNT request by adding an entry to the
+.I /var/lib/nfs/rmtab
+file.
+When receivng a UMNT request from an NFS client,
+.B rpc.mountd
+simply removes the matching entry from
+.IR /var/lib/nfs/rmtab ,
+as long as the access control list for that export allows that sender
+to access the export.
+.PP
+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
+.BR showmount (8)
+command.
+.BR showmount (8)
+uses other procedures in the NFS MOUNT protocol to report information
+about the server's exported file systems.
+.PP
+Note, however, that there is little to guarantee that the contents of
+.I /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
+.IR /var/lib/nfs/rmtab .
+.SS Mounting File Systems with NFSv4
+Version 4 (and later) of NFS does not use a separate NFS MOUNT
+protocol. Instead mounting is performed using regular NFS requests
+handled by the NFS server in the Linux kernel
+.RI ( nfsd ).
+Consequently
+.I /var/lib/nfs/rmtab
+is not updated to reflect any NFSv4 activity.
+.SH OPTIONS
+.TP
+.B \-d kind " or " \-\-debug kind
+Turn on debugging. Valid kinds are: all, auth, call, general and parse.
+.TP
+.BR \-l " or " \-\-log\-auth
+Enable logging of responses to authentication and access requests from
+nfsd. Each response is then cached by the kernel for 30 minutes (or as set by
+.B \-\-ttl
+below), and will be refreshed after 15 minutes (half the ttl time) if
+the relevant client remains active.
+Note that
+.B -l
+is equivalent to
+.B "-d auth"
+and so can be enabled in
+.B /etc/nfs.conf
+with
+.B "\[dq]debug = auth\[dq]"
+in the
+.B "[mountd]"
+section.
+.IP
+.B rpc.mountd
+will always log authentication responses to MOUNT requests when NFSv3 is
+used, but to get similar logs for NFSv4, this option is required.
+.TP
+.BR \-i " or " \-\-cache\-use\-ipaddr
+Normally each client IP address is matched against each host identifier
+(name, wildcard, netgroup etc) found in
+.B /etc/exports
+and a combined identity is formed from all matching identifiers.
+Often many clients will map to the same combined identity so performing
+this mapping reduces the number of distinct access details that the
+kernel needs to store.
+Specifying the
+.B \-i
+option suppresses this mapping so that access to each filesystem is
+requested and cached separately for each client IP address. Doing this
+can increase the burden of updating the cache slightly, but can make the
+log messages produced by the
+.B -l
+option easier to read.
+.TP
+.B \-T " or " \-\-ttl
+Provide a time-to-live (TTL) for cached information given to the kernel.
+The kernel will normally request an update if the information is needed
+after half of this time has expired. Increasing the provided number,
+which is in seconds, reduces the rate of cache update requests, and this
+is particularly noticeable when these requests are logged with
+.BR \-l .
+However increasing also means that changes to hostname to address
+mappings can take longer to be noticed.
+The default TTL is 1800 (30 minutes).
+.TP
+.B \-F " or " \-\-foreground
+Run in foreground (do not daemonize)
+.TP
+.B \-h " or " \-\-help
+Display usage message.
+.TP
+.B \-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.
+.TP
+.B \-N mountd-version " or " \-\-no-nfs-version mountd-version
+This option can be used to request that
+.B rpc.mountd
+do not offer certain versions of NFS. The current version of
+.B rpc.mountd
+can support both NFS version 2, 3 and 4. If the
+either one of these version should not be offered,
+.B rpc.mountd
+must be invoked with the option
+.B "\-\-no-nfs-version <vers>" .
+.TP
+.B \-n " or " \-\-no-tcp
+Don't advertise TCP for mount.
+.TP
+.B \-p num " or " \-P num " or " \-\-port num
+Specifies the port number used for RPC listener sockets.
+If this option is not specified,
+.B rpc.mountd
+will try to consult
+.IR /etc/services ,
+if gets port succeed, set the same port for all listener socket,
+otherwise chooses a random ephemeral port for each listener socket.
+.IP
+This option can be used to fix the port value of
+.BR rpc.mountd 's
+listeners when NFS MOUNT requests must traverse a firewall
+between clients and servers.
+.TP
+.B \-H " prog or " \-\-ha-callout prog
+Specify a high availability callout program.
+This program receives callouts for all MOUNT and UNMOUNT requests.
+This allows
+.B rpc.mountd
+to be used in a High Availability NFS (HA-NFS) environment.
+.IP
+The callout program is run with 4 arguments.
+The first is
+.B mount
+or
+.B 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.
+.IP
+This callout is not needed with 2.6 and later kernels.
+Instead, mount the nfsd filesystem on
+.IR /proc/fs/nfsd .
+.TP
+.BI "\-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
+.I /var/lib/nfs
+is used.
+.TP
+.BI "\-r," "" " \-\-reverse\-lookup"
+.B rpc.mountd
+tracks IP addresses in the
+.I rmtab
+file. When a DUMP request is made (by
+someone running
+.BR "showmount -a" ,
+for instance), it returns IP addresses instead
+of hostnames by default. This option causes
+.B 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.
+.TP
+.BR "\-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.
+.TP
+.B \-u " or " \-\-no-udp
+Don't advertise UDP for mounting
+.TP
+.B \-V version " or " \-\-nfs-version version
+This option can be used to request that
+.B rpc.mountd
+offer certain versions of NFS. The current version of
+.B rpc.mountd
+can support both NFS version 2 and the newer version 3.
+.TP
+.B \-v " or " \-\-version
+Print the version of
+.B rpc.mountd
+and exit.
+.TP
+.B \-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
+.B \-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
+.B newgroup
+command on the client will still be effective. This function requires
+a Linux Kernel with version at least 2.6.21.
+
+.SH CONFIGURATION FILE
+Many of the options that can be set on the command line can also be
+controlled through values set in the
+.B [mountd]
+or, in some cases, the
+.B [nfsd]
+sections of the
+.I /etc/nfs.conf
+configuration file.
+Values recognized in the
+.B [mountd]
+section include
+.BR manage-gids ,
+.BR cache\-use\-ipaddr ,
+.BR descriptors ,
+.BR port ,
+.BR threads ,
+.BR ttl ,
+.BR reverse-lookup ", and"
+.BR state-directory-path ,
+.B ha-callout
+which each have the same effect as the option with the same name.
+
+The values recognized in the
+.B [nfsd]
+section include
+.BR TCP ,
+.BR UDP ,
+.BR vers3 ", and"
+.B vers4
+which each have the same meaning as given by
+.BR rpc.nfsd (8).
+
+.SH TCP_WRAPPERS SUPPORT
+You can protect your
+.B rpc.mountd
+listeners using the
+.B tcp_wrapper
+library or
+.BR iptables (8).
+.PP
+Note that the
+.B tcp_wrapper
+library supports only IPv4 networking.
+.PP
+Add the hostnames of NFS peers that are allowed to access
+.B rpc.mountd
+to
+.IR /etc/hosts.allow .
+Use the daemon name
+.B mountd
+even if the
+.B rpc.mountd
+binary has a different name.
+.PP
+Hostnames used in either access file will be ignored when
+they can not be resolved into IP addresses.
+For further information see the
+.BR tcpd (8)
+and
+.BR hosts_access (5)
+man pages.
+.SS IPv6 and TI-RPC support
+TI-RPC is a pre-requisite for supporting NFS on IPv6.
+If TI-RPC support is built into
+.BR rpc.mountd ,
+it attempts to start listeners on network transports marked 'visible' in
+.IR /etc/netconfig .
+As long as at least one network transport listener starts successfully,
+.B rpc.mountd
+will operate.
+.SH FILES
+.TP 2.5i
+.I /etc/exports
+input file for
+.BR exportfs ,
+listing exports, export options, and access control lists
+.TP 2.5i
+.I /var/lib/nfs/rmtab
+table of clients accessing server's exports
+.SH SEE ALSO
+.BR exportfs (8),
+.BR exports (5),
+.BR showmount (8),
+.BR rpc.nfsd (8),
+.BR rpc.rquotad (8),
+.BR nfs (5),
+.BR nfs.conf (5),
+.BR tcpd (8),
+.BR hosts_access (5),
+.BR iptables (8),
+.BR netconfig (5)
+.sp
+RFC 1094 - "NFS: Network File System Protocol Specification"
+.br
+RFC 1813 - "NFS Version 3 Protocol Specification"
+.br
+RFC 7530 - "Network File System (NFS) Version 4 Protocol"
+.br
+RFC 8881 - "Network File System (NFS) Version 4 Minor Version 1 Protocol"
+.SH AUTHOR
+Olaf Kirch, H. J. Lu, G. Allan Morris III, and a host of others.