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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)
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