NFS(5)                     Linux Programmer's Manual                    NFS(5)
NAME
       nfs - nfs and nfs4 fstab format and options

SYNOPSIS
       /etc/fstab

DESCRIPTION
       The  fstab  file  contains information about which filesystems 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.

       Three different versions of the NFS protocol are supported by the Linux
       NFS client: NFS version 2, NFS version 3, and NFS version 4.  To  mount
       via  NFS version 2, use the nfs file system type and specify nfsvers=2.
       To mount via NFS version 3, use the nfs file system  type  and  specify
       nfsvers=3.   Version 3 is the default protocol version for the nfs file
       system type when nfsvers= is not specified on the  mount  command.   To
       mount  via  NFS version 4, use the nfs4 file system type.  The nfsvers=
       keyword is not supported for the nfs4 file system type.

       These file system types share similar mount  options;  the  differences
       are listed below.

       Here is an example from an /etc/fstab file for an NFSv2 mount over UDP.

       server:/usr/local/pub    /pub   nfs    rsize=32768,wsize=32768,timeo=14,intr

       Here is an example for an NFSv4 mount over TCP using Kerberos 5  mutual
       authentication.

       server:/usr/local/pub    /pub   nfs4   proto=tcp,sec=krb5,hard,intr

   Options for the nfs file system type
       rsize=n        The  number of bytes NFS uses when reading files from an
                      NFS server.  The rsize is negotiated between the  server
                      and client to determine the largest block size that both
                      can support.  The value specified by this option is  the
                      maximum  size  that  could  be used; however, the actual
                      size used may be smaller.  Note: Setting this size to  a
                      value  less  than  the largest supported block size will
                      adversely affect performance.

       wsize=n        The number of bytes NFS uses when writing  files  to  an
                      NFS  server.  The wsize is negotiated between the server
                      and client to determine the largest block size that both
                      can  support.  The value specified by this option is the
                      maximum size that could be  used;  however,  the  actual
                      size  used may be smaller.  Note: Setting this size to a
                      value less than the largest supported  block  size  will
                      adversely affect performance.

       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 seconds is reached or the enough
                      retransmissions have occured to cause a  major  timeout.
                      Then,  if the filesystem is hard mounted, each new time-
                      out cascade restarts at twice the initial value  of  the
                      previous cascade, again doubling at each retransmission.
                      The maximum timeout is always 60 seconds.  Better  over-
                      all  performance may be achieved by increasing the time-
                      out when mounting on a busy network, to a  slow  server,
                      or through several routers or gateways.

       retrans=n      The  number  of  minor timeouts and retransmissions that
                      must occur before a major timeout occurs.   The  default
                      is  3  timeouts.   When a major timeout occurs, the file
                      operation is either aborted or a "server not responding"
                      message is printed on the console.

       acregmin=n     The minimum time in seconds that attributes of a regular
                      file should be cached before requesting  fresh  informa-
                      tion 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 direc-
                      tory should be cached before requesting  fresh  informa-
                      tion from a server.  The default is 30 seconds.

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

       actimeo=n      Using  actimeo sets all of acregmin, acregmax, 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  for  forground mounts is 2 minutes.  The
                      default value for background mounts  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 charac-
                      ters.

       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.

       proto=n        Mount the NFS filesystem using a specific network
                      protocol instead of  the  default  TCP  protocol.
                      Valid protocol types are udp and tcp.

       mountport=n    The  numeric  value  of  the  mountd port.  moun-
                      thost=name The name of the host running mountd  .

       mountprog=n    Use  an  alternate  RPC program number to contact
                      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 contact
                      the mount daemon on the remote host.  This option
                      is  useful  for  hosts  that can run multiple NFS
                      servers.  The default value depends on which ker-
                      nel you are using.

       nfsprog=n      Use  an  alternate  RPC program number to contact
                      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 contact
                      the NFS daemon on the remote host.   This  option
                      is  useful  for  hosts  that can run multiple NFS
                      servers.  The default value depends on which ker-
                      nel you are using.

       vers=n         vers is an alternative to nfsvers and is compati-
                      ble with many other operating systems.

       nolock         Disable NFS locking. Do not  start  lockd.   This
                      has  to  be  used  with some old NFS servers that
                      don't support locking.

       bg             If the first NFS mount attempt times  out,  retry
                      the mount in the background.  After a mount oper-
                      ation is backgrounded, all subsequent  mounts  on
                      the  same NFS server will be backgrounded immedi-
                      ately, 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 comple-
                      ment of the  bg  option,  and  also  the  default
                      behavior.

       soft           If an NFS file operation has a major timeout then
                      report an I/O error to the calling program.   The
                      default  is  to continue retrying NFS file opera-
                      tions indefinitely.

       hard           If an NFS file operation has a major timeout then
                      report "server not responding" on the console and
                      continue  retrying  indefinitely.   This  is  the
                      default.

       intr           If  an NFS file operation has a major timeout and
                      it  is  hard  mounted,  then  allow  signals   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 inter-
                      rupted.

       posix          Mount the NFS filesystem using  POSIX  semantics.
                      This allows an NFS filesystem to properly support
                      the POSIX pathconf command by querying the  mount
                      server  for the maximum 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 significant  performance  penalty
                      but  it  allows  two different NFS clients to get
                      reasonable results when both clients are actively
                      writing to a common export on the server.

       noacl          Disables Access Control List (ACL) processing.

       resvport/noresvport
                      Specifies  whether  the  NFS  client should use a
                      privileged source port when communicating with an
                      NFS  server for this mount point.  If this option
                      is not specified, or the resvport option is spec-
                      ified,  the  NFS  client uses a privileged source
                      port.  If the noresvport option is specified, the
                      NFS client uses a non-privileged source port.

                      Using  non-privileged source ports helps increase
                      the maximum number of NFS mount points allowed on
                      a  client,  but NFS servers must be configured to
                      allow  clients  to  connect  via   non-privileged
                      source ports.

       sec=mode       Set the security flavor for this mount to "mode".
                      The default setting is sec=sys, which uses  local
                      unix uids and gids to authenticate NFS operations
                      (AUTH_SYS).  Other currently  supported  settings
                      are:  sec=krb5, which uses Kerberos V5 instead of
                      local unix uids and gids to  authenticate  users;
                      sec=krb5i,   which  uses  Kerberos  V5  for  user
                      authentication and performs integrity checking of
                      NFS  operations using secure checksums to prevent
                      data tampering; and sec=krb5p,  which  uses  Ker-
                      beros  V5  for  user authentication and integrity
                      checking, and encrypts  NFS  traffic  to  prevent
                      traffic  sniffing  (this  is the most secure set-
                      ting).  Note that there is a performance  penalty
                      when using integrity or privacy.

       tcp            Mount  the NFS filesystem using the TCP protocol.
                      This is the default protocol.

       udp            Mount the NFS filesystem using the  UDP  protocol
                      instead of the default TCP protocol.

       nordirplus     Disables NFSv3 READDIRPLUS RPCs. Use this options
                      when mounting servers that don't support or  have
                      broken READDIRPLUS implementations.

       nosharecache   As  of kernel 2.6.18, it is no longer possible to
                      mount the same  same  filesystem  with  different
                      mount options to a new mountpoint.  It was deemed
                      unsafe to do so,  since  cached  data  cannot  be
                      shared  between  the  two  mountpoints. In conse-
                      quence, files or directories that were common  to
                      both  mountpoint  subtrees could often be seen to
                      be out of sync following an update.
                      This option allows administrators to  select  the
                      pre-2.6.18   behaviour,   permitting   the   same
                      filesystem to be  mounted  with  different  mount
                      options.
                      Beware:  Use  of  this  option is not recommended
                      unless you are certain that  there  are  no  hard
                      links  or  subtrees  of  this mountpoint that are
                      mounted elsewhere.

       lookupcache=type
                      This option dictates how  directories  and  files
                      should  be  cached when they are accessed -- i.e.
                      "looked up" -- on the server.  A  lookup  can  be
                      either  positive  (directory/file  was  found) or
                      negative (directory/file  was  not  found);  both
                      types of lookups can be cached.

                      By  default,  both  positive and negative lookups
                      are cached ( lookupcache=all ).   lookupcache=pos
                      prevents  negative  lookups  from  being  cached,
                      while lookupcache=none prevents all lookups  from
                      being cached.

                      Note:  lookupcache=none can adversely affect per-
                      formance, but may be necessary  if  shared  files
                      created or deleted on the server need to be imme-
                      diately visible to any  applications  running  on
                      NFS clients.

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

   Options for the nfs4 file system type
       rsize=n        The  number of bytes nfs4 uses when reading files
                      from the server.  The rsize is negotiated between
                      the  server  and  client to determine the largest
                      block size that  both  can  support.   The  value
                      specified by this option is the maximum size that
                      could be used; however, the actual size used  may
                      be  smaller.   Note: Setting this size to a value
                      less than the largest supported block  size  will
                      adversely affect performance.

       wsize=n        The  number of bytes nfs4 uses when writing files
                      to the server.  The wsize is  negotiated  between
                      the  server  and  client to determine the largest
                      block size that  both  can  support.   The  value
                      specified by this option is the maximum size that
                      could be used; however, the actual size used  may
                      be  smaller.   Note: Setting this size to a value
                      less than the largest supported block  size  will
                      adversely affect performance.

       timeo=n        The  value  in  tenths of a second before sending
                      the first retransmission after  an  RPC  timeout.
                      The default value depends on whether proto=udp or
                      proto=tcp is in effect (see below).  The  default
                      value  for  UDP  is  7  tenths  of a second.  The
                      default value for TCP is 60 seconds.   After  the
                      first  timeout, the timeout is doubled after each
                      successive timeout until a maximum timeout of  60
                      seconds  is reached or the enough retransmissions
                      have occured to cause a major timeout.  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
                      retransmission.  The maximum timeout is always 60
                      seconds.

       retrans=n      The  number of minor timeouts and retransmissions
                      that must occur before a  major  timeout  occurs.
                      The  default  is  5  timeouts for proto=udp and 2
                      timeouts for proto=tcp.   When  a  major  timeout
                      occurs, the file operation is either aborted or a
                      "server not responding" message is printed on the
                      console.

       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, acregmax,
                      acdirmin, and acdirmax to the same value.   There
                      is no default value.

       retry=n        The number of minutes to retry an NFS mount oper-
                      ation in the foreground or background before giv-
                      ing  up.   The default value for forground mounts
                      is 2 minutes.  The default value  for  background
                      mounts  is  10000  minutes,  which is roughly one
                      week.

       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 registered with its portmapper,
                      the   standard  NFS  port  number  2049  is  used
                      instead.

       proto=n        Mount the NFS filesystem using a specific network
                      protocol  instead  of  the  default TCP protocol.
                      Valid protocol types are udp and tcp.   Many  NFS
                      version  4 servers only support the TCP protocol.

       clientaddr=n   On a multi-homed client, this causes  the  client
                      to  use a specific callback address when communi-
                      cating with an NFS version 4 server.  This option
                      is currently ignored.

       sec=mode       Same as sec=mode for the nfs filesystem type (see
                      above).

       bg             If an NFS mount  attempt  times  out,  retry  the
                      mount in the background.  After a mount operation
                      is backgrounded, all  subsequent  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 comple-
                      ment of the  bg  option,  and  also  the  default
                      behavior.

       soft           If an NFS file operation has a major timeout then
                      report an I/O error to the calling program.   The
                      default  is  to continue retrying NFS file opera-
                      tions indefinitely.

       hard           If an NFS file operation has a major timeout then
                      report "server not responding" on the console and
                      continue  retrying  indefinitely.   This  is  the
                      default.

       intr           If  an NFS file operation has a major timeout and
                      it  is  hard  mounted,  then  allow  signals   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 inter-
                      rupted.

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

       noac           Disable  attribute caching, and force synchronous
                      writes.   This  extracts  a  server   performance
                      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.

       nosharecache   As of kernel 2.6.18, it is no longer possible  to
                      mount  the  same  same  filesystem with different
                      mount options to a new mountpoint.  It was deemed
                      unsafe  to  do  so,  since  cached data cannot be
                      shared between the  two  mountpoints.  In  conse-
                      quence,  files or directories that were common to
                      both mountpoint subtrees could often be  seen  to
                      be out of sync following an update.
                      This  option  allows administrators to select the
                      pre-2.6.18   behaviour,   permitting   the   same
                      filesystem  to  be  mounted  with different mount
                      options.
                      Beware: Use of this  option  is  not  recommended
                      unless  you  are  certain  that there are no hard
                      links or subtrees of  this  mountpoint  that  are
                      mounted elsewhere.

       lookupcache=type
                      This  option  dictates  how directories and files
                      should be cached when they are accessed  --  i.e.
                      "looked  up"  --  on  the server. A lookup can be
                      either positive  (directory/file  was  found)  or
                      negative  (directory/file  was  not  found); both
                      types of lookups can be cached.

                      By default, both positive  and  negative  lookups
                      are  cached ( lookupcache=all ).  lookupcache=pos
                      prevents  negative  lookups  from  being  cached,
                      while  lookupcache=none prevents all lookups from
                      being cached.

                      Note: lookupcache=none can adversely affect  per-
                      formance,  but  may  be necessary if shared files
                      created or deleted on the server need to be imme-
                      diately  visible  to  any applications running on
                      NFS clients.

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

       All of the non-value options have corresponding nooption  forms.
       For  example,  nointr  means  don't  allow file operations 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 option is implemented but is currently ignored by  the
       Linux kernel.

       Checking  files on NFS filesystem referenced by file descriptors
       (i.e. the fcntl and ioctl families of  functions)  may  lead  to
       inconsistent result due to the lack of consistency check in ker-
       nel even if noac is used.

Linux 0.99                     20 November 1993                         NFS(5)