mount Command

NAME

       mount - mount a filesystem

SYNOPSIS

       mount [-lhV]

       mount -a [-fFnrsvw] [-t vfstype] [-O optlist]

       mount [-fnrsvw] [-o option[,option]...]  device|dir

       mount [-fnrsvw] [-t vfstype] [-o options] device dir

DESCRIPTION

       All files accessible in a Unix system are arranged in one big tree, the file hierarchy, rooted at /.  These files can be spread out  over  several  devices.  The mount command serves to attach the filesystem found on some device to the big file tree. Conversely, the umount(8)  command will detach it again.

The standard form of the mount command, is

              mount -t type device dir

This  tells  the kernel to attach the filesystem found on device (which is of type type) at the directory dir.  The previous contents (if  any) and  owner  and  mode  of  dir  become  invisible,  and as long as this filesystem remains mounted, the pathname dir refers to the root of  the filesystem on device.

The listing and help

              Three forms of invocation do not actually mount anything:

              mount –h          prints a help message

              mount –V          prints a version string

              mount [-l] [-t type]           lists all mounted filesystems (of type type).  The option -l adds the labels in this listing.  See below.

The device indication

Most devices are indicated by a file name (of  a  block  special device),  like /dev/sda1, but there are other possibilities. For example, in the case of an  NFS  mount,  device  may  look  like knuth.cwi.nl:/dir.   It  is possible to indicate a block special device using its volume LABEL or UUID (see the -L and -U options below).

The recommended setup is to use LABEL=<label> or UUID=<uuid> tags rather than /dev/disk/by-{label,uuid} udev symlinks in  the /etc/fstab   file.  The  tags  are  more  readable,  robust  and portable. The mount(8) command internally uses udev symlinks, so use   the   symlinks   in   /etc/fstab  is  not  advantage  over LABEL=/UUID=.  For more details see libblkid(3). The proc filesystem is not associated with a special device, and when mounting it, an arbitrary keyword, such as proc can be used instead of a device specification.  (The customary  choice  none is less fortunate: the error message ‘none busy’ from umount can be confusing.)

The /etc/fstab, /etc/mtab and /proc/mounts files. The file /etc/fstab (see fstab(5)), may contain lines describing what devices are usually mounted where, using which options.

              The command

                     mount -a [-t type] [-O optlist]

(usually given in a bootscript) causes all filesystems mentioned in fstab (of the proper type and/or having  or  not  having  the proper  options)  to  be  mounted as indicated, except for those whose line contains the noauto keyword.  Adding  the  -F  option will make mount fork, so that the filesystems are mounted simultaneously.

When mounting a file system mentioned in fstab or mtab, it suffices to give only the device, or only the mount point. The  programs  mount  and  umount  maintain  a list of currently mounted filesystems in the file /etc/mtab.  If no arguments  are given to mount, this list is printed. The  mount  program  does not read the /etc/fstab file if device (or LABEL/UUID) and dir are specified. For example:

                     mount /dev/foo /dir

If you want to override mount options from /etc/fstab  you  have to use:

            mount device|dir -o <options>

and then the mount options from command line will be appended to the list of options from /etc/fstab. The usual behavior is that the last option wins if there is more duplicated options. When the proc file system is mounted (say at /proc), the files /etc/mtab and /proc/mounts have very similar contents. The  former  has  somewhat  more  information, such as the mount options used, but is not  necessarily  up-to-date  (cf. the -n  option below).  It is possible to replace /etc/mtab by a symbolic link to /proc/mounts, and especially when you have very large numbers of mounts things will be much faster with that symlink, but some information is lost that way, and in particular using the "user" option will fail.

The non-superuser mounts

        Normally,  only  the  superuser can mount filesystems.  However, when fstab contains the user option on a line, anybody can mount the corresponding system.

              Thus, given a line

              /dev/cdrom  /cd  iso9660  ro,user,noauto,unhide

any  user  can  mount  the iso9660 filesystem found on his CDROM using the command

mount /dev/cdrom

              or

           mount /cd

For more details, see fstab(5).  Only the user  that  mounted  a filesystem  can unmount it again.  If any user should be able to unmount, then use users instead of user in the fstab line. The             owner option is similar to the user option, with the restriction that the user must be the owner of the special file. This may be useful e.g. for /dev/fd if a login script makes the console user              owner of this device.  The group option  is  similar,  with  the restriction  that  the  user  must be member of the group of the special file.

The bind mounts

       Since Linux 2.4.0 it is possible to remount  part  of  the  file hierarchy somewhere else. The call is mount --bind olddir newdir or shortoption

mount -B olddir newdir

           or fstab entry is:

       /olddir /newdir none bind

After this call the same contents is accessible in two places. One can also remount a single file (on a single file). This call attaches only (part of) a single filesystem, not  possible  submounts.  The entire file hierarchy including submounts is attached a second place using

mount --rbind olddir newdir

      or shortoption

      mount -R olddir newdir

Note that the filesystem mount options will remain the same as those  on  the  original  mount  point, and cannot be changed by passing the -o  option  along  with  --bind/--rbind.  The  mount              options  can be changed by a separate remount command, for example:

                     mount --bind olddir newdir

                     mount -o remount,ro newdir

The move operation

              Since Linux 2.5.1 it is possible to atomically move a mounted tree to another place. The call is

                     mount --move olddir newdir

                                  or shortoption

                     mount -M olddir newdir

This will cause the contents which previously appeared under olddir to be accessed under newdir.  The physical location of the files is not changed.

The shared subtrees operations

       Since Linux 2.6.15 it is possible to mark a mount and its submounts as shared, private, slave or unbindable. A shared mount provides  ability  to  create  mirrors  of  that mount such that             mounts and umounts within any of the mirrors  propagate  to  the other  mirror.  A slave mount receives propagation from its master, but any not vice-versa. A private mount carries no propagation  abilities. A unbindable mount is a private mount which cannot cloned through a bind operation.  Detailed  semantics  is documented in Documentation/sharedsubtree.txt file in the kernel source tree.

                     mount --make-shared mountpoint

                     mount --make-slave mountpoint

                     mount --make-private mountpoint

                     mount --make-unbindable mountpoint

The following commands allows one to recursively change the type of all the mounts under a given mountpoint.

                     mount --make-rshared mountpoint

                     mount --make-rslave mountpoint

                     mount --make-rprivate mountpoint

                     mount --make-runbindable mountpoint

COMMAND LINE OPTIONS

      The full set of mount options used by an invocation of mount is determined by first extracting the mount options for the filesystem from the fstab  table, then  applying any options specified by the -o argument, and finally applying a -r or -w option, when present.

Command line options available for the mount command:

-V, --version                            Output version.

-h, --help                                 Print a help message.

-v, --verbose                          Verbose mode.

-a, --all                                      Mount all filesystems (of the given types) mentioned in fstab.

-i, --internal-only                  Don’t  call  the  /sbin/mount.<filesystem>  helper  even  if  it exists.

-l                                                  Add the labels in the mount output. Mount must  have  permission to  read  the  disk device (e.g. be suid root) for this to work. One can set such a label  for  ext2,  ext3  or  ext4  using  the e2label(8)  utility, or for XFS using xfs_admin(8), or for reiserfs using reiserfstune(8).

-n, --no-mtab                         Mount without writing in /etc/mtab.  This is necessary for example when /etc is on a read-only filesystem.

-r, --read-only                        Mount the filesystem read-only. A synonym is -o ro.

Note that, depending on the filesystem type,  state  and  kernel behavior, the system may still write to the device. For example, Ext3 or ext4 will replay its journal if the filesystem is dirty. To prevent this kind of write access, you may want to mount ext3 or ext4 filesystem with "ro,noload" mount  options  or  set  the block device to read-only mode, see command blockdev(8).

     -w, --rw                                           Mount  the filesystem read/write. This is the default. A synonym is -o rw.

       -L label                                           Mount the partition that has the specified label.

       -U uuid                                          Mount the partition that has the specified uuid. These two options require the file /proc/partitions (present since Linux 2.1.116) to exist.