1rpc.mountd(8) System Manager's Manual rpc.mountd(8)
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6 rpc.mountd - NFS mount daemon
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9 /usr/sbin/rpc.mountd [options]
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12 The rpc.mountd daemon implements the server side of the NFS MOUNT pro‐
13 tocol, an NFS side protocol used by NFS version 2 [RFC1094] and NFS
14 version 3 [RFC1813].
15 An NFS server maintains a table of local physical file systems that are
17 accessible to NFS clients. Each file system in this table is referred
18 to as an exported file system, or export, for short.
19 Each file system in the export table has an access control list.
21 rpc.mountd uses these access control lists to determine whether an NFS
22 client is permitted to access a given file system. For details on how
23 to manage your NFS server's export table, see the exports(5) and
24 exportfs(8) man pages.
25 Mounting exported NFS File Systems
27 The NFS MOUNT protocol has several procedures. The most important of
28 these are MNT (mount an export) and UMNT (unmount an export).
29 A MNT request has two arguments: an explicit argument that contains the
31 pathname of the root directory of the export to be mounted, and an
32 implicit argument that is the sender's IP address.
33 When receiving a MNT request from an NFS client, rpc.mountd checks both
35 the pathname and the sender's IP address against its export table. If
36 the sender is permitted to access the requested export, rpc.mountd
37 returns an NFS file handle for the export's root directory to the
38 client. The client can then use the root file handle and NFS LOOKUP
39 requests to navigate the directory structure of the export.
40 The rmtab File
42 The rpc.mountd daemon registers every successful MNT request by adding
43 an entry to the /var/lib/nfs/rmtab file. When receivng a UMNT request
44 from an NFS client, rpc.mountd simply removes the matching entry from
45 /var/lib/nfs/rmtab, as long as the access control list for that export
46 allows that sender to access the export.
47 Clients can discover the list of file systems an NFS server is cur‐
49 rently exporting, or the list of other clients that have mounted its
50 exports, by using the showmount(8) command. showmount(8) uses other
51 procedures in the NFS MOUNT protocol to report information about the
52 server's exported file systems.
53 Note, however, that there is little to guarantee that the contents of
55 /var/lib/nfs/rmtab are accurate. A client may continue accessing an
56 export even after invoking UMNT. If the client reboots without sending
57 a UMNT request, stale entries remain for that client in
58 /var/lib/nfs/rmtab.
59
61 -d kind or --debug kind
62 Turn on debugging. Valid kinds are: all, auth, call, general and
63 parse.
64 -F or --foreground
66 Run in foreground (do not daemonize)
67 -h or --help
69 Display usage message.
70 -o num or --descriptors num
72 Set the limit of the number of open file descriptors to num. The
73 default is to leave the limit unchanged.
74 -N mountd-version or --no-nfs-version mountd-version
76 This option can be used to request that rpc.mountd do not offer
77 certain versions of NFS. The current version of rpc.mountd can
78 support both NFS version 2, 3 and 4. If the either one of these
79 version should not be offered, rpc.mountd must be invoked with
80 the option --no-nfs-version <vers> .
81 -n or --no-tcp
83 Don't advertise TCP for mount.
84 -p num or -P num or --port num
86 Specifies the port number used for RPC listener sockets. If
87 this option is not specified, rpc.mountd will try to consult
88 /etc/services, if gets port succeed, set the same port for all
89 listener socket, otherwise chooses a random ephemeral port for
90 each listener socket.
91 This option can be used to fix the port value of rpc.mountd's
93 listeners when NFS MOUNT requests must traverse a firewall
94 between clients and servers.
95 -H prog or --ha-callout prog
97 Specify a high availability callout program. This program
98 receives callouts for all MOUNT and UNMOUNT requests. This
99 allows rpc.mountd to be used in a High Availability NFS (HA-NFS)
100 environment.
101 The callout program is run with 4 arguments. The first is mount
103 or unmount depending on the reason for the callout. The second
104 will be the name of the client performing the mount. The third
105 will be the path that the client is mounting. The last is the
106 number of concurrent mounts that we believe the client has of
107 that path.
108 This callout is not needed with 2.6 and later kernels. Instead,
110 mount the nfsd filesystem on /proc/fs/nfsd.
111 -s, --state-directory-path directory
113 Specify a directory in which to place state information (etab
114 and rmtab). If this option is not specified the default of
115 /var/lib/nfs is used.
116 -r, --reverse-lookup
118 rpc.mountd tracks IP addresses in the rmtab file. When a DUMP
119 request is made (by someone running showmount -a, for instance),
120 it returns IP addresses instead of hostnames by default. This
121 option causes rpc.mountd to perform a reverse lookup on each IP
122 address and return that hostname instead. Enabling this can
123 have a substantial negative effect on performance in some situa‐
124 tions.
125 -t N or --num-threads=N or --num-threads N
127 This option specifies the number of worker threads that
128 rpc.mountd spawns. The default is 1 thread, which is probably
129 enough. More threads are usually only needed for NFS servers
130 which need to handle mount storms of hundreds of NFS mounts in a
131 few seconds, or when your DNS server is slow or unreliable.
132 -u or --no-udp
134 Don't advertise UDP for mounting
135 -V version or --nfs-version version
137 This option can be used to request that rpc.mountd offer certain
138 versions of NFS. The current version of rpc.mountd can support
139 both NFS version 2 and the newer version 3.
140 -v or --version
142 Print the version of rpc.mountd and exit.
143 -g or --manage-gids
145 Accept requests from the kernel to map user id numbers into
146 lists of group id numbers for use in access control. An NFS
147 request will normally (except when using Kerberos or other cryp‐
148 tographic authentication) contains a user-id and a list of
149 group-ids. Due to a limitation in the NFS protocol, at most 16
150 groups ids can be listed. If you use the -g flag, then the list
151 of group ids received from the client will be replaced by a list
152 of group ids determined by an appropriate lookup on the server.
153 Note that the 'primary' group id is not affected so a newgroup
154 command on the client will still be effective. This function
155 requires a Linux Kernel with version at least 2.6.21.
156
159 Many of the options that can be set on the command line can also be
160 controlled through values set in the [mountd] or, in some cases, the
161 [nfsd] sections of the /etc/nfs.conf configuration file. Values recog‐
162 nized in the [mountd] section include manage-gids, descriptors, port,
163 threads, reverse-lookup, and state-directory-path, ha-callout which
164 each have the same effect as the option with the same name.
165 The values recognized in the [nfsd] section include TCP, UDP, vers2,
167 vers3, and vers4 which each have same same meaning as given by
168 rpc.nfsd(8).
169
172 TI-RPC is a pre-requisite for supporting NFS on IPv6. If TI-RPC sup‐
173 port is built into rpc.mountd, it attempts to start listeners on net‐
174 work transports marked 'visible' in /etc/netconfig. As long as at
175 least one network transport listener starts successfully, rpc.mountd
176 will operate.
177
179 /etc/exports input file for exportfs, listing exports,
180 export options, and access control lists
181 /var/lib/nfs/rmtab table of clients accessing server's exports
183
185 exportfs(8), exports(5), showmount(8), rpc.nfsd(8), rpc.rquotad(8),
186 nfs(5), nfs.conf(5), tcpd(8), iptables(8), netconfig(5)
187 RFC 1094 - "NFS: Network File System Protocol Specification"
189 RFC 1813 - "NFS Version 3 Protocol Specification"
190
192 Olaf Kirch, H. J. Lu, G. Allan Morris III, and a host of others.
193 31 Dec 2009 rpc.mountd(8)