Skip site navigation (1)Skip section navigation (2)

FreeBSD Manual Pages


home | help
MOUNT(8)                FreeBSD System Manager's Manual               MOUNT(8)

     mount -- mount file systems

     mount [-adflpruvw] [-F fstab] [-o options] [-t ufs | external_type]
     mount [-dfpruvw] special | node
     mount [-dfpruvw] [-o options] [-t ufs | external_type] special node

     The mount utility calls the mount(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.  Excep-
             tions 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 deter-
             mine 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, also mount those
             file systems which are marked as ``late''.

     -o      Options are specified with a -o flag followed by a comma sepa-
             rated string of options.  In case of conflicting options being
             specified, the rightmost option takes effect.  The following
             options are available:

             acls    Enable Access Control Lists, or ACLS, which can be cus-
                     tomized via the setfacl(1) and getfacl(1) commands.

             async   All I/O to the file system should be done asynchronously.
                     This is a dangerous flag to set, since it does not guar-
                     antee 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 recov-
                     ery mechanism is present.

                     When used with the -u flag, this is the same as specify-
                     ing the options currently in effect for the mounted file

             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 specify-
                     ing 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.

                     Enable multi-label Mandatory Access Control, or MAC, on
                     the specified file system.  If the file system supports
                     multilabel operation, individual labels will be main-
                     tained 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 informa-
                     tion, which cause the multilabel mount flag to be set
                     automatically at mount-time.

                     Metadata I/O should be done synchronously, while data I/O
                     should be done asynchronously.  This is the default.

                     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 criti-
                     cal 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.

                     Disable read clustering.

                     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.

                     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).

             sync    All I/O to the file system should be done synchronously.

                     This option allows a snapshot of the specified file sys-
                     tem 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 con-
                     tained 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 interest-
                     ing 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 essen-
                          tially 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 sys-
                          tem 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

                          Further details can be found in the file at

                     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 secu-
                     rity 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.

             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 sys-
                     tem first.  If those operations fail due to a non-exis-
                     tent 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).  Options that take a value are speci-
             fied using the syntax -option=value.  For example, the mount com-

                   mount -t unionfs -o -b /sys $HOME/sys

             causes mount to execute the equivalent of:

                   /sbin/mount_unionfs -b /sys $HOME/sys

             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

     -r      The file system is to be mounted read-only.  Mount the file sys-
             tem 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 pre-
             fixed 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.

             If the type is not one of the internally known types, mount will
             attempt to execute a program in /sbin/mount_XXX where XXX is
             replaced by the 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.

     -w      The file system object is to be read and write.

     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

     /etc/fstab  file system table

     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

     getfacl(1), setfacl(1), mount(2), acl(3), mac(4), fstab(5), kldload(8),
     mount_cd9660(8), mount_devfs(8), mount_ext2fs(8), mount_fdescfs(8),
     mount_linprocfs(8), mount_msdosfs(8), mount_nfs(8), mount_ntfs(8),
     mount_nullfs(8), mount_nwfs(8), mount_portalfs(8), mount_procfs(8),
     mount_reiserfs(8), mount_smbfs(8), mount_std(8), mount_udf(8),
     mount_umapfs(8), mount_unionfs(8), umount(8)

     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).

     A mount utility appeared in Version 1 AT&T UNIX.

     It is possible for a corrupted file system to cause a crash.

FreeBSD 6.2                      July 12, 2006                     FreeBSD 6.2


Want to link to this manual page? Use this URL:

home | help