mnttab - mounted file system table
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
special mount_point fstype options time
The name of the resource that has been mounted.
The pathname of the directory on which the filesystem
The file system type of the mounted file system.
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).
The following ioctl(2) calls are supported:
Returns the count of mounted resources in the current
snapshot in the uint32_t pointed to by arg.
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
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.
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.
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
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.
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.
Usual mount point for mnttab file system
Header file that contains IOCTL definitions
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)
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-
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-
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
Man(1) output converted with