Manual Pages for UNIX Operating System command usage for man mnttab

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  TABs  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 sys-
                    tem.


     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



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File Formats                                            mnttab(4)



     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  identifies  the
                          file system and tag to be cleared.

                          Use of  this  ioctl  is  restricted  to



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File Formats                                            mnttab(4)



                          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 system 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 provided for legacy applications that  might
     have been using the dev=information option.






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File Formats                                            mnttab(4)



     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.


































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