NFS(5)              Linux Programmer's Manual              NFS(5)

NAME
       nfs - nfs fstab format and options

SYNOPSIS
       /etc/fstab

DESCRIPTION
       The  fstab  file contains information about which filesys-
       tems to mount  where  and  with  what  options.   For  NFS
       mounts,  it  contains  the server name and exported server
       directory to mount from, the local directory that  is  the
       mount point, and the NFS specific options that control the
       way the filesystem is mounted.

       Here is an example from an /etc/fstab  file  from  an  NFS
       mount.

       server:/usr/local/pub    /pub   nfs    rsize=8192,wsize=8192,timeo=14,intr

   Options
       rsize=n        The  number  of bytes NFS uses when reading
                      files from  an  NFS  server.   The  default
                      value is dependent on the kernel, currently
                      1024  bytes.    (However,   throughput   is
                      improved greatly by asking for rsize=8192.)

       wsize=n        The number of bytes NFS uses  when  writing
                      files  to an NFS server.  The default value
                      is dependent on the kernel, currently  1024
                      bytes.   (However,  throughput  is improved
                      greatly by asking for wsize=8192.)

       timeo=n        The value in  tenths  of  a  second  before
                      sending  the  first retransmission after an
                      RPC timeout.  The default value is 7 tenths
                      of  a second.  After the first timeout, the
                      timeout is doubled  after  each  successive
                      timeout  until a maximum timeout of 60 sec-
                      onds is reached or the  enough  retransmis-
                      sions  have  occured to cause a major time-
                      out.   Then,  if  the  filesystem  is  hard
                      mounted,  each new timeout cascade restarts
                      at twice the initial value of the  previous
                      cascade, again doubling at each retransmis-
                      sion.  The maximum  timeout  is  always  60
                      seconds.  Better overall performance may be
                      achieved by  increasing  the  timeout  when
                      mounting  on  a  busy  network,  to  a slow
                      server, or through several routers or gate-
                      ways.

       retrans=n      The  number  of minor timeouts and retrans-
                      missions that must  occur  before  a  major
                      timeout occurs.  The default is 3 timeouts.
                      When a major timeout occurs, the file oper-
                      ation  is  either  aborted or a "server not
                      responding" message is printed on the  con-
                      sole.

       acregmin=n     The minimum time in seconds that attributes
                      of a regular file should be  cached  before
                      requesting fresh information from a server.
                      The default is 3 seconds.

       acregmax=n     The maximum time in seconds that attributes
                      of  a  regular  file  can  be cached before
                      requesting fresh information from a server.
                      The default is 60 seconds.

       acdirmin=n     The minimum time in seconds that attributes
                      of a  directory  should  be  cached  before
                      requesting fresh information from a server.
                      The default is 30 seconds.

       acdirmax=n     The maximum time in seconds that attributes
                      of   a   directory  can  be  cached  before
                      requesting fresh information from a server.
                      The default is 60 seconds.

       actimeo=n      Using  actimeo sets all of acregmin, acreg-
                      max, acdirmin, and  acdirmax  to  the  same
                      value.  There is no default value.

       retry=n        The number of minutes to retry an NFS mount
                      operation in the foreground  or  background
                      before  giving  up.   The  default value is
                      10000 minutes, which is roughly one week.

       namlen=n       When an NFS server does not support version
                      two  of the RPC mount protocol, this option
                      can be used to specify the  maximum  length
                      of  a  filename  that  is  supported on the
                      remote filesystem.  This is used to support
                      the  POSIX pathconf functions.  The default
                      is 255 characters.

       port=n         The numeric value of the port to connect to
                      the NFS server on.  If the port number is 0
                      (the default) then query the remote  host's
                      portmapper  for the port number to use.  If
                      the remote host's NFS daemon is not  regis-
                      tered with its portmapper, the standard NFS
                      port number 2049 is used instead.

       mountport=n    The numeric value of the mountd port.

       mounthost=name The name of the host running mountd .

       mountprog=n    Use an alternate RPC program number to con-
                      tact  the  mount daemon on the remote host.
                      This option is useful for  hosts  that  can
                      run  multiple  NFS  servers.   The  default
                      value is 100005 which is the  standard  RPC
                      mount daemon program number.

       mountvers=n    Use an alternate RPC version number to con-
                      tact the mount daemon on the  remote  host.
                      This  option  is  useful for hosts that can
                      run  multiple  NFS  servers.   The  default
                      value is version 1.

       nfsprog=n      Use an alternate RPC program number to con-
                      tact the NFS daemon  on  the  remote  host.
                      This  option  is  useful for hosts that can
                      run  multiple  NFS  servers.   The  default
                      value  is  100003 which is the standard RPC
                      NFS daemon program number.

       nfsvers=n      Use an alternate RPC version number to con-
                      tact  the  NFS  daemon  on the remote host.
                      This option is useful for  hosts  that  can
                      run  multiple  NFS  servers.   The  default
                      value is version 2.

       bg             If the first NFS mount attempt  times  out,
                      retry the mount in the background.  After a
                      mount operation is backgrounded, all subse-
                      quent mounts on the same NFS server will be
                      backgrounded  immediately,  without   first
                      attempting  the  mount.   A  missing  mount
                      point is treated as a timeout, to allow for
                      nested NFS mounts.

       fg             If  the  first NFS mount attempt times out,
                      retry the mount in the foreground.  This is
                      the  complement  of the bg option, and also
                      the default behavior.

       soft           If an NFS file operation has a major  time-
                      out then report an I/O error to the calling
                      program.  The default is to continue retry-
                      ing NFS file operations indefinitely.

       hard           If  an NFS file operation has a major time-
                      out then report "server not responding"  on
                      the  console  and continue retrying indefi-
                      nitely.  This is the default.

       intr           If an NFS file operation has a major  time-
                      out and it is hard mounted, then allow sig-
                      nals to interupt  the  file  operation  and
                      cause  it  to  return  EINTR to the calling
                      program.  The default is to not allow  file
                      operations to be interrupted.

       posix          Mount the NFS filesystem using POSIX seman-
                      tics.  This allows  an  NFS  filesystem  to
                      properly support the POSIX pathconf command
                      by querying the mount server for the  maxi-
                      mum  length of a filename.  To do this, the
                      remote host must support version two of the
                      RPC  mount protocol.  Many NFS servers sup-
                      port only version one.

       nocto          Suppress the retrieval  of  new  attributes
                      when creating a file.

       noac           Disable  all  forms  of  attribute  caching
                      entirely.  This extracts a  server  perfor-
                      mance  penalty  but it allows two different
                      NFS clients to get reasonable good  results
                      when  both  clients are actively writing to
                      common filesystem on the server.

       tcp            Mount the NFS filesystem using the TCP pro-
                      tocol  instead of the default UDP protocol.
                      Many NFS severs only support UDP.

       udp            Mount the NFS filesystem using the UDP pro-
                      tocol.  This is the default.

       All  of  the non-value options have corresponding nooption
       forms.  For example, nointr means don't allow file  opera-
       tions to be interrupted.

FILES
       /etc/fstab

SEE ALSO
       fstab(5), mount(8), umount(8), exports(5)

AUTHOR
       "Rick Sladkey" <jrs@world.std.com>

BUGS
       The  posix, and nocto options are parsed by mount but cur-
       rently are silently ignored.

       The tcp and namlen options are  implemented  but  are  not
       currently supported by the Linux kernel.

       The  umount  command  should notify the server when an NFS
       filesystem is unmounted.

Linux 0.99               20 November 1993                       1