mount8

Usage

Overview

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)).

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.