command invokes a file system-specific
program to prepare and graft the special
device on to the file system tree at the point
, or to update options for an
already-mounted file system.
argument is always interpreted as a
directory in the name space of currently mounted file systems. The
argument is interpreted in different
ways by the programs that handle different file system types; for example,
interprets it as a device node,
interprets it as a directory name,
interprets it as reference to a remote host and a directory on that host, and
The system maintains a list of currently mounted file systems. This list is
printed if mount
is invoked with no arguments,
and with no options that require some other behaviour.
If exactly one of special
is provided, then the missing
information (including the file system type) is taken from the
The provided argument is looked up first in the “fs_file”, then
in the “fs_spec” column. If the matching entry in
the string “
” as its
“fs_spec” field, the device or remote file system already
mounted at the location specified by “fs_spec” will be used.
If both special
are provided, then
not used. In this case, if the file system type is not specified via the
flag, then mount
may determine the type from the disk label (see
In addition, if special
contains a colon
’) or at sign
’), then the
type is inferred, but this behaviour is
deprecated, and will be removed in a future version of
, the file-system mounting policy is dictated
by the running security models. The default security model may allow
unprivileged mounting; see
The options are as follows:
- Causes mount to try to mount
all of the file systems listed in the
file except those for which the “noauto” option is
- Similar to the -A flag, except
that if a file system (other than the root file system) appears to be
already mounted, mount will not try to mount
it again. mount assumes that a file system is
already mounted if a file system with the same type is mounted on the
given mount point. More stringent checks are not possible because some
file system types report strange values for the mounted-from device for
mounted file systems.
- Causes everything to be done except for the invocation of
the file system-specific program. This option is useful in conjunction
with the -v flag to determine what the
mount command is trying to do.
- Forces the revocation of write access when trying to
downgrade a file system mount status from read-write to read-only.
- Options are specified with a
-o flag followed by a comma separated string
of options. The following options are available:
Any additional options specific to a given file system type (see the
-t option) may be passed as a comma separated
list; these options are distinguished by a leading “-”
(dash). Options that take a value are specified using the syntax
-option=value. For example, the mount command:
- All I/O to the file system should be done
asynchronously. In the event of a crash, it
is impossible for the system to verify the integrity of data on a file
system mounted with this option. You should only use this option
if you have an application-specific data recovery mechanism, or are
willing to recreate the file system from scratch.
- Clear async mode.
- Use DISCARD/TRIM commands if disk and driver support
EXPERIMENTAL - negatively influences
filesystem performance by increasing fragmentation, causes free block
map inconsistency on unclean shutdown, and is incompatible with
log. If log
option is also used, discard is
- Enable extended attributes, if the filesystem supports
them and does not enable them by default. Currently this is only the
case for UFS1.
- 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.
- Retrieves the file system specific mount arguments for
the given mounted file system and prints them.
- By setting the
MNT_IGNORE flag, causes the mount
point to be excluded from the list of file systems shown by default
- Never update the access time field for files. This
option is useful for optimizing read performance on file systems that
are used as news spools.
- This file system should be skipped when mount is run
with the -a flag.
- Do not allow programs to create crash dumps (core
files) on the file system. This option can be used to help protect
sensitive data by keeping core files (which may contain sensitive
data) from being created on insecure file systems. Only core files
that would be created by program crashes are prevented by use of this
flag; the behavior of
is not affected.
- Do not interpret character or block special devices on
the file system. This option is useful for a server that has file
systems containing special devices for architectures other than its
- Do not update modification times on device special
files. This option is useful on laptops or other systems that perform
- 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.
- Do not allow set-user-identifier or
set-group-identifier bits to take effect.
- (NFS only) Use the specified NFS port.
- The same as -r; mount the
file system read-only (even the super-user may not write it).
- Reload all incore data for a file system. This is used
mainly after running
on the root file system and finding things to fix. The file system
must be mounted read-only. All cached meta-data are invalidated,
superblock and summary information is re-read from disk, all cached
inactive vnodes and file data are invalidated and all inode data are
re-read for all active vnodes.
- Instead of running mount_type to mount the file system,
run rump_type. This uses a userspace server to mount the file system
and does not require kernel support for the specific file system type.
See the -t flag and respective rump_type
manual page for more information.
- (FFS only) Mount the file system with
meta-data journaling, also known simply as logging. It provides rapid
metadata updates and eliminates the need to check file system
consistency after a system outage. It requires the
WAPBL option to be enabled in the
running kernel. See
for more information. This option requires the “UFS2”
(level 4) superblock layout, which is the default for newly created
FFSv1 and FFSv2 file systems. To update an old file system with an
earlier superblock format, use the -c
log cannot be used together with
A file system mounted with log can be
mounted also with async, but such
filesystem behaves the same as if async
was not specified - meta-data writes use the log, hence its integrity
is still guaranteed.
- Recognize permission of symbolic link when reading or
- All I/O to the file system should be done
synchronously. This is not equivalent to the normal mode in which only
metadata is written synchronously.
- Clear sync mode.
- Causes the namespace at the mount point to appear as
the union of the mounted file system root (referred to as the
upper layer), and the existing directory
(referred to as the lower layer). Name
lookups will be done in the upper layer first. If a name does not
exist in the upper layer, then the name will be looked up in the lower
layer. If a name exists in both the upper and lower layers, then only
the upper instance is accessible. Creation of new files is done in the
upper layer, except in the case of the fdesc file system (see
Note that the union option can be applied
to any type of file system, and is fundamentally different from
which is a particular type of file system. Also note that the
union option affects the file system name
space only at the mount point itself; it does not apply recursively to
- The same as -u; indicate
that the status of an already mounted file system should be
causes mount to execute the equivalent of:
mount -t mfs -o nosuid,-N,-s=32m swap /tmp
/sbin/mount_mfs -o nosuid -N -s 32m swap /tmp
- 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
“rdonly” argument to the -o
- The argument following the -t
is used to indicate the file system type. The type
ffs 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 MFS.
mount will attempt to execute a program in
where XXX is replaced by the type name. For
example, nfs file systems are mounted by the program
- 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 first extracting the options for the file system from the
file, then applying any options specified by the
-o argument, and finally applying the
-r or -w
- Verbose mode. If this flag is specified more than once,
then the file system-specific mount arguments are printed for the given
mounted file system.
- The file system object is to be read and write.
The options specific to the various file system types are described in the
manual pages for those file systems' mount_XXX
commands; for instance, the options specific to Berkeley Fast File System
(FFS) are described in the
The particular type of file system in each partition of a disk can be found by
examining the disk label with the
- file system table
Some useful examples:
mount -t cd9660 -r /dev/cd0a /cdrom
mount -t msdos /dev/fd0a /floppy
mount -t nfs nfs-server-host:/directory/path /mount-point
- MFS (32 megabyte)
mount -t mfs -o nosuid,-s=32m swap /tmp
The “noauto” directive in /etc/fstab
can be used to make it easy to manually mount and unmount removable media
using just the mountpoint filename, with an entry like this:
/dev/cd0a /cdrom cd9660 ro,noauto 0
That would allow a simple command like “mount /cdrom” or
“umount /cdrom” for media using the ISO-9660 file system format
in the first CD-ROM drive.
The error “Operation not supported by device” indicates that the
mount for the specified file-system type cannot be completed because the
kernel lacks support for the said file-system. See
The error “Operation not permitted” may indicate that the mount
options include privileged options and/or do not include options that exclude
privileged options. One should try using at least “nodev” and
“nosuid” in such cases:
mount -t cd9660 -o nodev,nosuid /dev/cd0a /mnt
command appeared in
Version 1 AT&T UNIX