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 -f export-file or --exports-file export-file
69 This option specifies the exports file, listing the clients that
70 this server is prepared to serve and parameters to apply to each
71 such mount (see exports(5)). By default, export information is
72 read from /etc/exports.
73 -h or --help
75 Display usage message.
76 -o num or --descriptors num
78 Set the limit of the number of open file descriptors to num. The
79 default is to leave the limit unchanged.
80 -N mountd-version or --no-nfs-version mountd-version
82 This option can be used to request that rpc.mountd do not offer
83 certain versions of NFS. The current version of rpc.mountd can
84 support both NFS version 2, 3 and 4. If the either one of these
85 version should not be offered, rpc.mountd must be invoked with
86 the option --no-nfs-version <vers> .
87 -n or --no-tcp
89 Don't advertise TCP for mount.
90 -p num or -P num or --port num
92 Specifies the port number used for RPC listener sockets. If
93 this option is not specified, rpc.mountd chooses a random
94 ephemeral port for each listener socket.
95 This option can be used to fix the port value of rpc.mountd's
97 listeners when NFS MOUNT requests must traverse a firewall
98 between clients and servers.
99 -H prog or --ha-callout prog
101 Specify a high availability callout program. This program
102 receives callouts for all MOUNT and UNMOUNT requests. This
103 allows rpc.mountd to be used in a High Availability NFS (HA-NFS)
104 environment.
105 The callout program is run with 4 arguments. The first is mount
107 or unmount depending on the reason for the callout. The second
108 will be the name of the client performing the mount. The third
109 will be the path that the client is mounting. The last is the
110 number of concurrent mounts that we believe the client has of
111 that path.
112 This callout is not needed with 2.6 and later kernels. Instead,
114 mount the nfsd filesystem on /proc/fs/nfsd.
115 -s, --state-directory-path directory
117 Specify a directory in which to place statd state information.
118 If this option is not specified the default of /var/lib/nfs is
119 used.
120 -r, --reverse-lookup
122 rpc.mountd tracks IP addresses in the rmtab file. When a DUMP
123 request is made (by someone running showmount -a, for instance),
124 it returns IP addresses instead of hostnames by default. This
125 option causes rpc.mountd to perform a reverse lookup on each IP
126 address and return that hostname instead. Enabling this can
127 have a substantial negative effect on performance in some situa‐
128 tions.
129 -t N or --num-threads=Nor --num-threads N
131 This option specifies the number of worker threads that
132 rpc.mountd spawns. The default is 1 thread, which is probably
133 enough. More threads are usually only needed for NFS servers
134 which need to handle mount storms of hundreds of NFS mounts in a
135 few seconds, or when your DNS server is slow or unreliable.
136 -V version or --nfs-version version
138 This option can be used to request that rpc.mountd offer certain
139 versions of NFS. The current version of rpc.mountd can support
140 both NFS version 2 and the newer version 3.
141 -v or --version
143 Print the version of rpc.mountd and exit.
144 -g or --manage-gids
146 Accept requests from the kernel to map user id numbers into
147 lists of group id numbers for use in access control. An NFS
148 request will normally (except when using Kerberos or other cryp‐
149 tographic authentication) contains a user-id and a list of
150 group-ids. Due to a limitation in the NFS protocol, at most 16
151 groups ids can be listed. If you use the -g flag, then the list
152 of group ids received from the client will be replaced by a list
153 of group ids determined by an appropriate lookup on the server.
154 Note that the 'primary' group id is not affected so a newgroup
155 command on the client will still be effective. This function
156 requires a Linux Kernel with version at least 2.6.21.
157
159 You can protect your rpc.mountd listeners using the tcp_wrapper library
160 or iptables(8).
161 Note that the tcp_wrapper library supports only IPv4 networking.
163 Add the hostnames of NFS peers that are allowed to access rpc.mountd to
165 /etc/hosts.allow. Use the daemon name mountd even if the rpc.mountd
166 binary has a different name.
167 Hostnames used in either access file will be ignored when they can not
169 be resolved into IP addresses. For further information see the tcpd(8)
170 and hosts_access(5) man pages.
171 IPv6 and TI-RPC support
173 TI-RPC is a pre-requisite for supporting NFS on IPv6. If TI-RPC sup‐
174 port is built into rpc.mountd, it attempts to start listeners on net‐
175 work transports marked 'visible' in /etc/netconfig. As long as at
176 least one network transport listener starts successfully, rpc.mountd
177 will operate.
178
180 /etc/exports input file for exportfs, listing exports,
181 export options, and access control lists
182 /var/lib/nfs/rmtab table of clients accessing server's exports
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186 exportfs(8), exports(5), showmount(8), rpc.nfsd(8), rpc.rquotad(8),
187 nfs(5), tcpd(8), hosts_access(5), iptables(8), netconfig(5)
188 RFC 1094 - "NFS: Network File System Protocol Specification"
190 RFC 1813 - "NFS Version 3 Protocol Specification"
191
193 Olaf Kirch, H. J. Lu, G. Allan Morris III, and a host of others.
194 31 Dec 2009 rpc.mountd(8)