MOUNT(8) FreeBSD System Manager's Manual MOUNT(8)
NAME
mount - mount file systems
SYNOPSIS
mount [--libxo] [-adflpruvw] [-F fstab] [-o options]
[-t [no]type[,type ...]]
mount [--libxo] [-dfpruvw] special | node
mount [--libxo] [-dfpruvw] [-o options] [-t [no]type[,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:
--libxo
Generate output via libxo(3) in a selection of different human
and machine readable formats. See xo_options(7) for details on
command line arguments.
-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 fstab
Specify the fstab file to use.
-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, mount only those
file systems which are marked as "late".
-l When used in conjunction with the -a option, also mount those
file systems which are marked as "late".
-n For compatibility with some other implementations, this flag is
currently a no-op.
-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.
atime Update the file access time when reading from a file.
This is the default.
automounted
This flag indicates that the file system was mounted by
automountd(8). Automounted file systems are
automatically unmounted by autounmountd(8).
autoro Mount the file system read-write. If that fails with an
error that suggests that the media could be read-only,
then automatically try to mount the file system read-
only.
current
When used with the -u flag, this is the same as
specifying the options currently in effect for the
mounted file system.
emptydir
Require that the mount point directory be empty.
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/cd0 /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.
nocover
Do not mount if the requested mount point is already the
root of a mount point.
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 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.
This option is intended to be used when mounting file
systems from untrusted external storage systems or public
writable /tmp file systems. You can still create or
remove symlinks, or read the value of a symbolic link.
ro Mount the filesystem read-only, even the super-user may
not write it. Equivalent to -r.
rw Mount the filesystem read-write.
snapshot
Take a snapshot of the specified filesystem. When this
option is used, all other options are ignored. The -u
flag is required with this option.
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:
1. 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.
2. 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.
3. 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.
untrusted
The file system is untrusted and the kernel should use
more extensive checks on the file-system's metadata
before using it. This option is intended to be used when
mounting file systems from untrusted media such as USB
memory sticks or other externally-provided media.
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 [no]type[,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:
mount -a -t nonfs,nullfs
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, nullfs, smbfs, udf, and unionfs mount will not call
nmount(2) directly and will instead attempt to execute a program
in /sbin/mount_type where type 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
EXAMPLES
Remount the root filesystem with read-write permissions:
mount -uw /
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), lsvfs(1), setfacl(1), nmount(2), symlink(2), acl(3),
getmntinfo(3), libxo(3), xo_options(7), cd9660(4), devfs(4), ext2fs(4),
ffs(4), mac(4), p9fs(4), procfs(4), tarfs(4), tmpfs(4), fstab(5),
symlink(7), automount(8), fstyp(8), kldload(8), mount_cd9660(8),
mount_msdosfs(8), mount_nfs(8), mount_nullfs(8), mount_smbfs(8),
mount_udf(8), mount_unionfs(8), quotacheck(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.
The -p option will not list userquota or groupquota items from fstab(5)
because they are not true mount options and are not information returned
by getmntinfo(3). At boot quotacheck(8), processes these items.
FreeBSD 15.1-STABLE-HBSD May 15, 2026 MOUNT(8)