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mnttab(4)                        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 getmn-
       tent(3C). Mounting a file system adds an entry to this table.  Unmount-
       ing  removes  an entry from this table. Remounting a file system causes
       the information in the mounted file  system  table  to  be  updated  to
       reflect  any  changes  caused by the remount. The list is maintained by
       the kernel in order of mount time. That is, the first mounted file sys-
       tem  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  regu-
       lar file containing the current mnttab information.

       Each entry is a line of fields separated by <&lt;TAB>&gt;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 pathname 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  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.

           Use   of   this   ioctl   is   restricted  to  processes  with  the
           {PRIV_SYS_MOUNT} privilege.



       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 iden-
           tifies the file system and tag to be cleared.

           Use  of  this  ioctl  is   restricted   to   processes   with   the
           {PRIV_SYS_MOUNT} privilege.



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 sys-
                               tem too long.



       EPERM                   The   calling    process    does    not    have
                               {PRIV_SYS_MOUNT}   privilege   and   either   a
                               MNTIOC_SETTAG or MNTIOC_CLRTAG call was made.



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 pro-
       vided for legacy applications that might have been using the dev=infor-
       mation option.

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

       Applications  requiring device number information for mounted file sys-
       tems should use the getextmntent(3C) interface, which  functions  prop-
       erly in either 32- or 64-bit environments.

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 mod-
       ification  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 different  from  the
       most recent snapshot since the mnttab file was opened.



SunOS 5.10                        20 Dec 2003                        mnttab(4)