MNTTAB(5) File Formats and Configurations MNTTAB(5)

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 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
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 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 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(8).

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 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

ioctl(2), poll(2), read(2), stat(2), getmntent(3C), mkfile(8),
mount(8), mount_hsfs(8), mount_nfs(8), mount_pcfs(8), mount_ufs(8)

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 environments.

Applications requiring device number information for mounted file
systems should use the getextmntent(3C) interface, which functions
properly 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
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 different
from the most recent snapshot since the mnttab file was opened.

September 8, 2015 MNTTAB(5)