NAME¶
mount —
mount file systems
SYNOPSIS¶
mount |
[-adflpruvw]
[-o
options]
[-t ufs |
external_type] |
mount |
[-dfpruvw]
special | node |
mount |
[-dfpruvw]
[-o
options]
[-t ufs |
external_type] special
node |
DESCRIPTION¶
The
mount utility calls the
nmount(2) system
call to prepare and graft a
special device or the remote
node (rhost:path) on to the file system tree at the point
node. If either
special or
node are not provided, the appropriate information is
taken from the
fstab(5) file.
The system maintains a list of currently mounted file systems. If no arguments
are given to
mount, this list is printed.
The options are as follows:
- -a
- All the file systems described in
fstab(5) are mounted. Exceptions are those marked as
“
noauto
”, those marked as
“late
” (unless the
-l option was specified), those excluded by the
-t flag (see below), or if they are already mounted
(except the root file system which is always remounted to preserve
traditional single user mode behavior).
- -d
- Causes everything to be done except for the actual system
call. This option is useful in conjunction with the -v
flag to determine what the mount command is trying to
do.
- -f
- Forces the revocation of write access when trying to
downgrade a file system mount status from read-write to read-only. Also
forces the R/W mount of an unclean file system (dangerous; use with
caution).
- -l
- When used in conjunction with the -a
option, also mount those file systems which are marked as
“
late
”.
- -o
- Options are specified with a -o flag
followed by a comma separated string of options. In case of conflicting
options being specified, the rightmost option takes effect. The following
options are available:
- acls
- Enable POSIX.1e Access Control Lists, or ACLs, which
can be customized via the setfacl(1) and
getfacl(1) commands. This flag is mutually exclusive
with nfsv4acls flag.
- async
- All I/O to the file system should be done
asynchronously. This is a dangerous flag to set,
since it does not guarantee that the file system structure on the disk
will remain consistent. For this reason, the async
flag should be used sparingly, and only when some data recovery
mechanism is present.
- current
- When used with the -u flag, this is
the same as specifying the options currently in effect for the mounted
file system.
- force
- The same as -f; forces the revocation
of write access when trying to downgrade a file system mount status
from read-write to read-only. Also forces the R/W mount of an unclean
file system (dangerous; use with caution).
- fstab
- When used with the -u flag, this is
the same as specifying all the options listed in the
fstab(5) file for the file system.
- late
- This file system should be skipped when
mount is run with the -a flag but
without the -l flag.
- mountprog=⟨program⟩
- Force mount to use the specified
program to mount the file system, instead of calling
nmount(2) directly. For example:
mount -t foofs -o mountprog=/mydir/fooprog /dev/acd0 /mnt
- multilabel
- Enable multi-label Mandatory Access Control, or MAC, on
the specified file system. If the file system supports multilabel
operation, individual labels will be maintained for each object in the
file system, rather than using a single label for all objects. An
alternative to the -l flag in
tunefs(8). See mac(4) for more
information, which cause the multilabel mount flag to be set
automatically at mount-time.
- nfsv4acls
- Enable NFSv4 ACLs, which can be customized via the
setfacl(1) and getfacl(1)
commands. This flag is mutually exclusive with acls
flag.
- noasync
- Metadata I/O should be done synchronously, while data
I/O should be done asynchronously. This is the default.
- noatime
- Do not update the file access time when reading from a
file. This option is useful on file systems where there are large
numbers of files and performance is more critical than updating the
file access time (which is rarely ever important). This option is
currently only supported on local file systems.
- noauto
- This file system should be skipped when
mount is run with the -a
flag.
- noclusterr
- Disable read clustering.
- noclusterw
- Disable write clustering.
- noexec
- Do not allow execution of any binaries on the mounted
file system. This option is useful for a server that has file systems
containing binaries for architectures other than its own. Note: This
option was not designed as a security feature and no guarantee is made
that it will prevent malicious code execution; for example, it is
still possible to execute scripts which reside on a
noexec mounted partition.
- nosuid
- Do not allow set-user-identifier or
set-group-identifier bits to take effect. Note: this option is
worthless if a public available suid or sgid wrapper like
suidperl(1) is installed on your system. It is set
automatically when the user does not have super-user privileges.
- nosymfollow
- Do not follow symlinks on the mounted file system.
- ro
- The same as -r; mount the file system
read-only (even the super-user may not write it).
- snapshot
- This option allows a snapshot of the specified file
system to be taken. The -u flag is required with
this option. Note that snapshot files must be created in the file
system that is being snapshotted. You may create up to 20 snapshots
per file system. Active snapshots are recorded in the superblock, so
they persist across unmount and remount operations and across system
reboots. When you are done with a snapshot, it can be removed with the
rm(1) command. Snapshots may be removed in any
order, however you may not get back all the space contained in the
snapshot as another snapshot may claim some of the blocks that it is
releasing. Note that the schg flag is set on snapshots to ensure that
not even the root user can write to them. The unlink command makes an
exception for snapshot files in that it allows them to be removed even
though they have the schg flag set, so it is not necessary to clear
the schg flag before removing a snapshot file.
Once you have taken a snapshot, there are three interesting things that
you can do with it:
- Run
fsck(8) on the snapshot file. Assuming that the
file system was clean when it was mounted, you should always get a
clean (and unchanging) result from running fsck on the snapshot.
This is essentially what the background fsck process does.
- Run
dump(8) on the snapshot. You will get a dump
that is consistent with the file system as of the timestamp of the
snapshot.
- Mount the snapshot as
a frozen image of the file system. To mount the snapshot
/var/snapshot/snap1:
mdconfig -a -t vnode -f /var/snapshot/snap1 -u 4
mount -r /dev/md4 /mnt
You can now cruise around your frozen /var file
system at /mnt. Everything will be in the same
state that it was at the time the snapshot was taken. The one
exception is that any earlier snapshots will appear as zero length
files. When you are done with the mounted snapshot:
umount /mnt
mdconfig -d -u 4
- suiddir
- A directory on the mounted file system will respond to
the SUID bit being set, by setting the owner of any new files to be
the same as the owner of the directory. New directories will inherit
the bit from their parents. Execute bits are removed from the file,
and it will not be given to root.
This feature is designed for use on fileservers serving PC users via
ftp, SAMBA, or netatalk. It provides security holes for shell users
and as such should not be used on shell machines, especially on home
directories. This option requires the SUIDDIR option in the kernel to
work. Only UFS file systems support this option. See
chmod(2) for more information.
- sync
- All I/O to the file system should be done
synchronously.
- update
- The same as -u; indicate that the
status of an already mounted file system should be changed.
- union
- Causes the namespace at the mount point to appear as
the union of the mounted file system root and the existing directory.
Lookups will be done in the mounted file system first. If those
operations fail due to a non-existent file the underlying directory is
then accessed. All creates are done in the mounted file system.
Any additional options specific to a file system type that is not one of the
internally known types (see the -t option) may be passed
as a comma separated list; these options are distinguished by a leading
“-” (dash). For example, the mount command:
mount -t cd9660 -o -e /dev/cd0 /cdrom
causes mount to execute the equivalent of:
/sbin/mount_cd9660 -e /dev/cd0 /cdrom
Options that take a value are specified using the -option=value syntax:
mount -t msdosfs -o -u=fred,-g=wheel /dev/da0s1 /mnt
is equivalent to
/sbin/mount_msdosfs -u fred -g wheel /dev/da0s1 /mnt
Additional options specific to file system types which are not internally
known (see the description of the -t option below) may
be described in the manual pages for the associated
/sbin/mount_XXX utilities.
- -p
- Print mount information in fstab(5)
format. Implies also the -v option.
- -r
- The file system is to be mounted read-only. Mount the file
system read-only (even the super-user may not write it). The same as the
ro argument to the -o option.
- -t
ufs | external_type
- The argument following the -t is used to
indicate the file system type. The type ufs is the
default. The -t option can be used to indicate that the
actions should only be taken on file systems of the specified type. More
than one type may be specified in a comma separated list. The list of file
system types can be prefixed with “
no
”
to specify the file system types for which action should
not be taken. For example, the mount
command:
mounts all file systems except those of type NFS and NULLFS.
The default behavior of mount is to pass the
-t option directly to the nmount(2)
system call in the fstype
option.
However, for the following file system types: cd9660,
mfs, msdosfs, nfs,
ntfs, nwfs, nullfs,
oldnfs, portalfs,
smbfs, udf, and
unionfs, mount will not call
nmount(2) directly and will instead attempt to execute a
program in /sbin/mount_XXX where
XXX is replaced by the file system type name. For
example, nfs file systems are mounted by the program
/sbin/mount_nfs.
Most file systems will be dynamically loaded by the kernel if not already
present, and if the kernel module is available.
- -u
- The -u flag indicates that the status of
an already mounted file system should be changed. Any of the options
discussed above (the -o option) may be changed; also a
file system can be changed from read-only to read-write or vice versa. An
attempt to change from read-write to read-only will fail if any files on
the file system are currently open for writing unless the
-f flag is also specified. The set of options is
determined by applying the options specified in the argument to
-o and finally applying the -r or
-w option.
- -v
- Verbose mode. If the -v is used alone,
show all file systems, including those that were mounted with the
MNT_IGNORE
flag and show additional information
about each file system (including fsid when run by root).
- -w
- The file system object is to be read and write.
ENVIRONMENT¶
PATH_FSTAB
- If the environment variable
PATH_FSTAB
is set, all operations are performed
against the specified file. PATH_FSTAB
will not be
honored if the process environment or memory address space is considered
“tainted”. (See issetugid(2) for more
information.)
FILES¶
- /etc/fstab
- file system table
DIAGNOSTICS¶
Various, most of them are self-explanatory.
XXXXX file system is not available
The kernel does not support the respective file system type. Note that support
for a particular file system might be provided either on a static (kernel
compile-time), or dynamic basis (loaded as a kernel module by
kldload(8)).
SEE ALSO¶
getfacl(1),
setfacl(1),
nmount(2),
acl(3),
mac(4),
devfs(5),
ext2fs(5),
fstab(5),
procfs(5),
kldload(8),
mount_cd9660(8),
mount_msdosfs(8),
mount_nfs(8),
mount_ntfs(8),
mount_nullfs(8),
mount_nwfs(8),
mount_portalfs(8),
mount_smbfs(8),
mount_udf(8),
mount_unionfs(8),
umount(8),
zfs(8),
zpool(8)
HISTORY¶
A
mount utility appeared in
Version 1
AT&T UNIX.
CAVEATS¶
After a successful
mount, the permissions on the original
mount point determine if
.. is accessible from the mounted
file system. The minimum permissions for the mount point for traversal across
the mount point in both directions to be possible for all users is 0111
(execute for all).
Use of the
mount is preferred over the use of the file system
specific
mount_XXX commands. In
particular,
mountd(8) gets a
SIGHUP
signal (that causes an update of the export list) only when the file system is
mounted via
mount.
BUGS¶
It is possible for a corrupted file system to cause a crash.