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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  re-
       flect  any changes caused by the	remount. The list is maintained	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
       containing 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 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 mi-
	   nor 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  al-
			       ready  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 MN-
			       TIOC_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 op-
       tion  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)

NAME | DESCRIPTION | IOCTLS | ERRORS | FILES | SEE ALSO | WARNINGS | NOTES

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