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File Formats                                            mnttab(4)



NAME
     mnttab - mounted file system table

DESCRIPTION
     The file /etc/mnttab is really a file system  that  provides
     read-only  access  to  the table of mounted file systems for
     the current host. /etc/mnttab is read by programs using  the
     routines  described in getmntent(3C). Mounting a file system
     adds an entry to this table.  Unmounting  removes  an  entry
     from  this table. Remounting a file system causes the infor-
     mation in the mounted file system table  to  be  updated  to
     reflect any changes caused by the remount. The list is main-
     tained by the kernel in order of mount time.  That  is,  the
     first  mounted file system is first in the list and the most
     recently mounted file system is  last.  When  mounted  on  a
     mount  point  the file system appears as a regular file con-
     taining the current mnttab information.

     Each entry is a line of fields separated by  <TAB>s  in  the
     form:

     special   mount_point   fstype   options   time


     where:

     special
           The name of the resource that has been mounted.

     mount_point
           The pathname of the directory on which the  filesystem
           is mounted.

     fstype
           The file system type of the mounted file system.

     options
           The mount options. See respective  mount  file  system
           man page in the SEE ALSO section below.

     time  The time at which the file system was mounted.

     Examples of entries for the special field include the  path-
     name  of  a  block-special device, the name of a remote file
     system in the form of host:pathname, or the name of  a  swap
     file, for example, a file made with mkfile(1M).

IOCTLS
     The following ioctl(2) calls are supported:

     MNTIOC_NMNTS
           Returns the count of mounted resources in the  current



SunOS 5.9           Last change: 18 Feb 2003                    1






File Formats                                            mnttab(4)



           snapshot in the uint32_t pointed to by arg.

     MNTIOC_GETDEVLIST
           Returns an array of uint32_t's that is twice  as  long
           as  the  length returned by MNTIOC_NMNTS. Each pair of
           numbers  is the major and minor device number for  the
           file system at the corresponding
            line in the current /etc/mnttab snapshot. arg  points
           to  the  memory  buffer  to  receive the device number
           information.

     MNTIOC_SETTAG
           Sets a tag word into the options list  for  a  mounted
           file  system.  A tag is a notation that will appear in
           the options string of a mounted file system but it  is
           not recognized or interpreted by the file system code.
           arg points to a filled  in  mnttagdesc  structure,  as
           shown in the following example:


     uint_t  mtd_major; /* major number for mounted fs */
     uint_t  mtd_minor; /* minor number for mounted fs */
     char    *mtd_mntpt; /* mount point of file system */
     char    *mtd_tag;  /* tag to set/clear */

          If the tag already exists then it is marked as set  but
          not re-added. Tags can be at most MAX_MNTOPT_TAG long.

     MNTIOC_CLRTAG
           Marks a tag in the options list  for  a  mounted  file
           system as not set. arg points to the same structure as
           MNTIOC_SETTAG, which identifies the  file  system  and
           tag to be cleared.

ERRORS
     EFAULT
           The arg pointer in an MNTIOC_ ioctl call pointed to an
           inaccessible memory location or a character pointer in
           a mnttagdesc  structure  pointed  to  an  inaccessible
           memory location.

     EINVAL
           The tag specified  in  a  MNTIOC_SETTAG  call  already
           exists  as  a file system option, or the tag specified
           in a MNTIOC_CLRTAG call does not exist.

     ENAMETOOLONG
           The tag specified in a MNTIOC_SETTAG call is too  long
           or  the  tag would make the total length of the option
           string for the mounted file system too long.





SunOS 5.9           Last change: 18 Feb 2003                    2






File Formats                                            mnttab(4)



FILES
     /etc/mnttab
           Usual mount point for mnttab file system

     /usr/include/sys/mntio.h
           Header file that contains IOCTL definitions

SEE ALSO
     mkfile(1M),        mount_cachefs(1M),        mount_hsfs(1M),
     mount_nfs(1M),   mount_pcfs(1M),  mount_ufs(1M),  mount(1M),
     ioctl(2), read(2), poll(2), stat(2), getmntent(3C)

WARNINGS
     The mnttab file system provides the previously  undocumented
     dev=xxx  option  in  the option string for each mounted file
     system. This is provided for legacy applications that  might
     have been using the dev=information option.

     Using dev=option in applications  is  strongly  discouraged.
     The  device  number string represents a  32-bit quantity and
     might not contain correct  information  in  64-bit  environ-
     ments.

     Applications requiring device number information for mounted
     file  systems  should  use  the  getextmntent(3C) interface,
     which functions properly in either 32-  or  64-bit  environ-
     ments.

NOTES
     The snapshot of the mnttab information is taken any  time  a
     read(2)  is  performed  at  offset  0 (the beginning) of the
     mnttab file. The file modification time returned by  stat(2)
     for  the  mnttab  file  is  the  time  of the last change to
     mounted file  system  information.  A  poll(2)  system  call
     requesting  a POLLRDBAND event can be used to block and wait
     for the system's mounted file system information to be  dif-
     ferent  from  the most recent snapshot since the mnttab file
     was opened.

















SunOS 5.9           Last change: 18 Feb 2003                    3