Provided by: mount_2.12r-4ubuntu6_i386 bug

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.
       Version 2 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 3, use the nfs file system  type  and  specify  nfsvers=3.   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=8192,wsize=8192,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  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 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.   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
                      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
                      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 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
                      registered 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 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 kernel 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 kernel you are using.

       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  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 complement 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 operations 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 interrupted.

       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 support 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.

       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  Kerberos  V5  for
                      user authentication and integrity checking, and encrypts
                      NFS traffic to prevent traffic  sniffing  (this  is  the
                      most  secure setting).  Note that there is a performance
                      penalty when using integrity or privacy.

       tcp            Mount the NFS filesystem using the TCP protocol  instead
                      of  the  default  UDP  protocol.   Many NFS servers only
                      support UDP.

       udp            Mount the NFS filesystem using the UDP  protocol.   This
                      is the default.

       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 NFS uses when reading files from  an
                      NFS  server.   The  default  value  is  dependent on the
                      kernel, currently 4096 bytes.  (However,  throughput  is
                      improved greatly by asking for rsize=32768.)  This value
                      is negotiated with the server.

       wsize=n        The number of bytes NFS uses when writing  files  to  an
                      NFS  server.   The  default  value  is  dependent on the
                      kernel, currently 4096 bytes.  (However,  throughput  is
                      improved greatly by asking for wsize=32768.)  This value
                      is negotiated with the server.

       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 operation in
                      the foreground or  background  before  giving  up.   The
                      default  value  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 UDP protocol.  Many  NFS
                      version  4  servers  only  support  TCP.  Valid protocol
                      types are udp and tcp.

       clientaddr=n   On a multi-homed client, this causes the client to use a
                      specific callback address when communicating 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 complement 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 operations 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 interrupted.

       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.

       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, and nocto options are parsed  by  mount  but  currently  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.