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NFS(5)			   Linux Programmers 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.
       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  ker
		      nel,  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 ker
		      nel, 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 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  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 hosts portmapper for the port number
		      to use.  If the remote hosts 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 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 dont support lock
		      ing.

       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 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 sup
		      port 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 dont 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  ker
		      nel,  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  ker
		      nel,  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 opera
		      tion is either aborted or a "server not responding" mes
		      sage 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 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 hosts portmapper for the port number
		      to  use.	 If  the  remote  hosts  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 proto
		      col  instead of the default UDP protocol.  Many NFS ver
		      sion 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  back
		      grounded, all subsequent mounts on the same  NFS	server
		      will be backgrounded immediately, without first attempt
		      ing 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 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 dont allow file operations to be interrupted.

FILES
       /etc/fstab

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

AUTHOR
       "Rick Sladkey" 

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  sup
       ported by the Linux kernel.

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



Linux 0.99		       20 November 1993 			NFS(5)




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