1rpc.mountd(8)               System Manager's Manual              rpc.mountd(8)
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NAME

6       rpc.mountd - NFS mount daemon
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SYNOPSIS

9       /usr/sbin/rpc.mountd [options]
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DESCRIPTION

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].
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16       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.
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20       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
26   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).
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30       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.
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34       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.
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41   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.
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48       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.
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54       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.
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OPTIONS

61       -d kind  or  --debug kind
62              Turn on debugging. Valid kinds are: all, auth, call, general and
63              parse.
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65       -F  or  --foreground
66              Run in foreground (do not daemonize)
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68       -h  or  --help
69              Display usage message.
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71       -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.
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75       -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> .
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82       -n  or  --no-tcp
83              Don't advertise TCP for mount.
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85       -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.
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92              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.
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96       -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
102              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.
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109              This callout is not needed with 2.6 and later kernels.  Instead,
110              mount the nfsd filesystem on /proc/fs/nfsd.
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112       -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.
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117       -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.
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126       -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.
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133       -u  or  --no-udp
134              Don't advertise UDP for mounting
135
136       -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.
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141       -v  or  --version
142              Print the version of rpc.mountd and exit.
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144       -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.
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157

CONFIGURATION FILE

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.
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166       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).
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IPv6 and TI-RPC support

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.
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FILES

179       /etc/exports             input  file  for  exportfs,  listing  exports,
180                                export options, and access control lists
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182       /var/lib/nfs/rmtab       table of clients accessing server's exports
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SEE ALSO

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
188       RFC 1094 - "NFS: Network File System Protocol Specification"
189       RFC 1813 - "NFS Version 3 Protocol Specification"
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AUTHOR

192       Olaf Kirch, H. J. Lu, G. Allan Morris III, and a host of others.
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196                                  31 Dec 2009                    rpc.mountd(8)
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