MOUNT(8)

NAME
mount - mount a file system

SYNOPSIS
mount [-hV]

mount -a [-fFnrsvw] [-t vfstype]
mount [-fnrsvw] [-o options [,...]] 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 file system 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 file system 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 file system remains mounted, the pathname dir refers to the root of the file system on device. Three forms of invocation do not actually mount anything:
    mount -h
prints a help message;
    mount -V
prints a version string; and just
    mount [-t type]
lists all mounted file systems (of type type) - see below. The proc file system 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.) 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. The file /etc/fstab (see fstab(5)), may contain lines describing what devices are usually mounted where, using which options. This file is used in three ways:

(i) The command
    mount -a [-t type]
(usually given in a bootscript) causes all file systems mentioned in fstab (of the proper type) 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.

(ii) When mounting a file system mentioned in fstab, it suffices to give only the device, or only the mount point.

(iii) Normally, only the superuser can mount file systems. However, when fstab contains the user option on a line, then anybody can mount the corresponding system.

Thus, given a line
    /dev/cdrom /cd iso9660 ro,user,noauto,unhide
any user can mount the iso9660 file system found on his CDROM using the command
    mount /dev/cdrom
or
    mount /cd
For more details, see fstab(5). The programs mount and umount maintain a list of currently mounted file systems in the file /etc/mtab. If no arguments are given to mount, this list is printed. When the proc filesystem 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, but some information is lost that way, and in particular working with the loop device will be less convenient.

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

-V  Output version.

-h  Print a help message.

-v  Verbose mode.

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

-F  (Used in conjunction with -a.) Fork off a new incarnation of mount for each device. This will do the mounts on different devices or different NFS servers in parallel. This has the advantage that it is faster; also NFS timeouts go in parallel. A disadvantage is that the mounts are done in undefined order. Thus, you cannot use this option if you want to mount both /usr and /usr/spool.

-f  Causes everything to be done except for the actual system call; if it's not obvious, this ``fakes'' mounting the file system. This option is useful in conjunction with the -v flag to determine what the mount command is trying to do. It can also be used to add entries for devices that were mounted earlier with the -n option.

-n  Mount without writing in /etc/mtab. This is necessary for example when /etc is on a read-only file system.

-s  Tolerate sloppy mount options rather than failing. This will ignore mount options not supported by a filesystem type. Not all filesystems support this option. This option exists for support of the Linux autofs-based automounter.

-r  Mount the file system read-only. A synonym is -o ro.

-w  Mount the file system read/write. This is the default. A synonym is -o rw.

-t vfstype
    The argument following the -t is used to indicate the file system type. The file system types which are currently supported are listed in linux/fs/filesystems.c: minix, ext, ext2, xiafs, hpfs, msdos, umsdos, vfat, proc, nfs, iso9660, smbfs, ncpfs, affs, ufs, romfs, sysv, xenix, coherent. Note that the last three are equivalent and that xenix and coherent will be removed at some point in the future — use sysv instead. Since kernel version 2.1.21 the types ext and xiafs do not exist anymore. The type iso9660 is the default. If no -t option is given, or if the auto type is specified, the superblock is probed for the filesystem type (minix, ext, ext2, xiafs, iso9660, romfs are supported). If this probe fails and /proc/filesystems exists, then all of the filesystems listed there will be tried, except for those that are labeled "nodev" (e.g., proc and nfs). Note that the auto type may be useful for user-mounted floppies. Warning: the probing uses a heuristic (the presence of appropriate `magic'), and could recognize the wrong filesystem 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 on which no action should be taken. (This can be meaningful with the -a option.) For example, the command:
        mount -a -t nomsdos,ext
    mounts all file systems except those of type msdos and ext.

-o  Options are specified with a -o flag followed by a comma separated string of options. Some of these options are only useful when they appear in the /etc/fstab file. The following options apply to any file system that is being mounted:

    async
        All I/O to the file system should be done asynchronously.

    atime
        Update inode access time for each access. This is the default.

    auto
        Can be mounted with the -a option.

    defaults
        Use default options: rw, suid, dev, exec, auto, nouser, and async.

    dev Interpret character or block special devices on the file system.

    exec
        Permit execution of binaries.

    noatime
        Do not update inode access times on this file system (e.g, for faster access on the news spool to speed up news servers).

    noauto
        Can only be mounted explicitly (i.e., the -a option will not cause the file system to be mounted).

    nodev
        Do not interpret character or block special devices on the file system.

    noexec
        Do not allow execution of any binaries on the mounted file system. This option might be useful for a server that has file systems containing binaries for architectures other than its own.

    nosuid
        Do not allow set-user-identifier or set-group-identifier bits to take effect.

    nouser
        Forbid an ordinary (i.e., non-root) user to mount the file system. This is the default.

    remount
        Attempt to remount an already-mounted file system. This is commonly used to change the mount flags for a file system, especially to make a readonly file system writeable.

    ro  Mount the file system read-only.

    rw  Mount the file system read-write.

    suid
        Allow set-user-identifier or set-group-identifier bits to take effect.

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

    user
        Allow an ordinary user to mount the file system. This option implies the options noexec, nosuid, and nodev (unless overridden by subsequent options, as in the option line user,exec,dev,suid).

FILESYSTEM SPECIFIC MOUNT OPTIONS
The following options apply only to certain file systems. We sort them by file system. They all follow the -o flag.

Mount options for affs

uid=value and gid=value
    Set the owner and group of the root of the file system (default: uid=gid=0, but with option uid or gid without specified value, the uid and gid of the current process are taken).

setuid=value and setgid=value
    Set the owner and group of all files.

mode=value
    Set the mode of all files to value & 0777 disregarding the original permissions. Add search permission to directories that have read permission. The value is given in octal.

protect
    Do not allow any changes to the protection bits on the file system.

usemp
    Set uid and gid of the root of the file system to the uid and gid of the mount point upon the first sync or umount, and then clear this option. Strange...

verbose
    Print an informational message for each successful mount.

prefix=string
    Prefix used before volume name, when following a link.

volume=string
    Prefix (of length at most 30) used before '/' when following a symbolic link.

reserved=value
    (Default: 2.) Number of unused blocks at the start of the device.

root=value
    Give explicitly the location of the root block.

bs=value
    Give blocksize. Allowed values are 512, 1024, 2048, 4096.

grpquota / noquota / quota / usrquota
    These options are accepted but ignored.

Mount options for coherent
None.

Mount options for ext
None. Note that the `ext' file system is obsolete. Don't use it. Since Linux version 2.1.21 extfs is no longer part of the kernel source.

Mount options for ext2
The `ext2' file system is the standard Linux file system. Due to a kernel bug, it may be mounted with random mount options (fixed in Linux 2.0.4).

bsddf / minixdf
    Set the behaviour for the statfs system call. The minixdf behaviour is to return in the f_blocks field the total number of blocks of the file system, while the bsddf behaviour (which is the default) is to subtract the overhead blocks used by the ext2 file system and not available for file storage. Thus
% mount /k -o minixdf; df /k; umount /k
Filesystem   1024-blocks  Used Available Capacity Mounted on
/dev/sda6      2630655   86954  2412169      3%   /k
% mount /k -o bsddf; df /k; umount /k
Filesystem   1024-blocks  Used Available Capacity Mounted on
/dev/sda6      2543714      13  2412169      0%   /k
(Note that this example shows that one can add command line options to the options given in /etc/fstab.)

check / check=normal / check=strict
    Set checking level. When at least one of these options is set (and check=normal is set by default) the inodes and blocks bitmaps are checked upon mount (which can take half a minute or so on a big disk). With strict checking, block deallocation checks that the block to free is in the data zone.

check=none / nocheck
    No checking is done.

debug
    Print debugging info upon each (re)mount.

errors=continue / errors=remount-ro / errors=panic
    Define the behaviour when an error is encountered. (Either ignore errors and just mark the file system erroneous and continue, or remount the file system read-only, or panic and halt the system.) The default is set in the filesystem superblock, and can be changed using tune2fs(8).

grpid or bsdgroups / nogrpid or sysvgroups
    These options define what group id a newly created file gets. When grpid is set, it takes the group id of the directory in which it is created; otherwise (the default) it takes the fsgid of the current process, unless the directory has the setgid bit set, in which case it takes the gid from the parent directory, and also gets the setgid bit set if it is a directory itself.

resgid=n and resuid=n
    The ext2 file system reserves a certain percentage of the available space (by default 5%, see mke2fs(8) and tune2fs(8)). These options determine who can use the reserved blocks. (Roughly: whoever has the specified uid, or belongs to the specified group.)

sb=n
    Instead of block 1, use block n as superblock. This could be useful when the filesystem has been damaged. Usually, copies of the superblock are found every 8192 blocks: in block 1, 8193, 16385, ... (Thus, one gets hundreds or even thousands of copies of the superblock on a big filesystem. I do not know of options to mke2fs that would cause fewer copies to be written.)

grpquota / noquota / quota / usrquota
    These options are accepted but ignored.

Mount options for fat
(Note: fat is not a separate filesystem, but a common part of the msdos, umsdos and vfat filesystems.)

blocksize=512 / blocksize=1024
    Set blocksize (default 512).

uid=value and gid=value
    Set the owner and group of all files. (Default: the uid and gid of the current process.)

umask=value
    Set the umask (the bitmask of the permissions that are not present). The default is the umask of the current process. The value is given in octal.

check=value
    Three different levels of pickyness can be chosen:

    r[elaxed]
        Upper and lower case are accepted and equivalent, long name parts are truncated (e.g. verylongname.foobar becomes verylong.foo), leading and embedded spaces are accepted in each name part (name and extension).

    n[ormal]
        Like "relaxed", but many special characters (*, ?, <, spaces, etc.) are rejected. This is the default.

    s[trict]
        Like "normal", but names may not contain long parts and special characters that are sometimes used on Linux, but are not accepted by MS-DOS are rejected. (+, =, spaces, etc.)

conv=b[inary] / conv=t[ext] / conv=a[uto]
    The fat file system can perform CRLF<-->NL (MS-DOS text format to UNIX text format) conversion in the kernel. The following conversion modes are available:

    binary
        no translation is performed. This is the default.

    text
        CRLF<-->NL translation is performed on all files.

    auto
        CRLF<-->NL translation is performed on all files that don't have a "well-known binary" extension. The list of known extensions can be found at the beginning of fs/fat/misc.c (as of 2.0, the list is: exe, com, bin, app, sys, drv, ovl, ovr, obj, lib, dll, pif, arc, zip, lha, lzh, zoo, tar, z, arj, tz, taz, tzp, tpz, gz, tgz, deb, gif, bmp, tif, gl, jpg, pcx, tfm, vf, gf, pk, pxl, dvi).

    Programs that do computed lseeks won't like in-kernel text conversion. Several people have had their data ruined by this translation. Beware! For file systems mounted in binary mode, a conversion tool (fromdos/todos) is available.

debug
    Turn on the debug flag. A version string and a list of file system parameters will be printed (these data are also printed if the parameters appear to be inconsistent).

fat=12 / fat=16
    Specify either a 12 bit fat or a 16 bit fat. This overrides the automatic FAT type detection routine. Use with caution!

quiet
    Turn on the quiet flag. Attempts to chown or chmod files do not return errors, although they fail. Use with caution!

sys_immutable, showexec, dots, nodots, dotsOK=[yes|no]
    Various misguided attempts to force Unix or DOS conventions onto a FAT file system.

Mount options for hpfs

uid=value and gid=value
    Set the owner and group of all files. (Default: the uid and gid of the current process.)

umask=value
    Set the umask (the bitmask of the permissions that are not present). The default is the umask of the current process. The value is given in octal.

case=lower / case=asis
    Convert all files names to lower case, or leave them. (Default: case=lower.)

conv=binary / conv=text / conv=auto
    For conv=text, delete some random CRs (in particular, all followed by NL) when reading a file. For conv=auto, choose more or less at random between conv=binary and conv=text. For conv=binary, just read what is in the file. This is the default.

nocheck
    Do not abort mounting when certain consistency checks fail.

Mount options for iso9660
Normal iso9660 filenames appear in a 8.3 format (i.e., DOS-like restrictions on filename length), and in addition all characters are in upper case. Also there is no field for file ownership, protection, number of links, provision for block/character devices, etc. Rock Ridge is an extension to iso9660 that provides all of these unix like features. Basically there are extensions to each directory record that supply all of the additional information, and when Rock Ridge is in use, the filesystem is indistinguishable from a normal UNIX file system (except that it is read-only, of course).

norock
    Disable the use of Rock Ridge extensions, even if available. Cf. map.

check=r[elaxed] / check=s[trict]
    With check=relaxed, a filename is first converted to lower case before doing the lookup. This is probably only meaningful together with norock and map=normal. (Default: check=strict.)

uid=value and gid=value
    Give all files in the file system the indicated user or group id, possibly overriding the information found in the Rock Ridge extensions. (Default: uid=0,gid=0.)

map=n[ormal] / map=o[ff]
    For non-Rock Ridge volumes, normal name translation maps upper to lower case ASCII, drops a trailing `;1', and converts `;' to `.'. With map=off no name translation is done. See norock. (Default: map=normal.)

mode=value
    For non-Rock Ridge volumes, give all files the indicated mode. (Default: read permission for everybody.) Since Linux 2.1.37 one no longer needs to specify the mode in decimal. (Octal is indicated by a leading 0.)

unhide
    Also show hidden and associated files.

block=[512|1024|2048]
    Set the block size to the indicated value. (Default: block=1024.)

conv=a[uto] / conv=b[inary] / conv=m[text] / conv=t[ext]
    (Default: conv=binary.) Since Linux 1.3.54 this option has no effect anymore. (And non-binary settings used to be very dangerous, often leading to silent data corruption.)

cruft
    If the high byte of the file length contains other garbage, set this mount option to ignore the high order bits of the file length. This implies that a file cannot be larger than 16MB. The `cruft' option is set automatically if the entire CDROM has a weird size (negative, or more than 800MB). It is also set when volume sequence numbers other than 0 or 1 are seen.

Mount options for minix
None.

Mount options for msdos
See mount options for fat. If the msdos file system detects an inconsistency, it reports an error and sets the file system read-only. The file system can be made writeable again by remounting it.

Mount options for ncp
Just like nfs, the ncp implementation expects a binary argument (a struct ncp_mount_data) to the mount system call. This argument is constructed by ncpmount(8) and the current version of mount (2.6h) does not know anything about ncp.

Mount options for nfs
Instead of a textual option string, parsed by the kernel, the nfs file system expects a binary argument of type struct nfs_mount_data. The program mount itself parses the following options of the form `tag=value', and puts them in the structure mentioned: rsize=n, wsize=n, timeo=n, retrans=n, acregmin=n, acregmax=n, acdirmin=n, acdirmax=n, actimeo=n, retry=n, port=n, mountport=n, mounthost=name, mountprog=n, mountvers=n, nfsprog=n, nfsvers=n, namlen=n. The option addr=n is accepted but ignored. Also the following Boolean options, possibly preceded by no are recognized: bg, fg, soft, hard, intr, posix, cto, ac, tcp, udp, lock. For details, see nfs(5). Especially useful options include

rsize=8192,wsize=8192
    This will make your nfs connection much faster than with the default buffer size of 1024.

hard
    The program accessing a file on a NFS mounted file system will hang when the server crashes. The process cannot be interrupted or killed unless you also specify intr. When the NFS server is back online the program will continue undisturbed from where it was. This is probably what you want.

soft
    This option allows the kernel to time out if the nfs server is not responding for some time. The time can be specified with timeo=time. This option might be useful if your nfs server sometimes doesn't respond or will be rebooted while some process tries to get a file from the server. Usually it just causes lots of trouble.

nolock
    Do not use locking. Do not start lockd.

Mount options for proc

uid=value and gid=value
    These options are recognized, but have no effect as far as I can see.

Mount options for romfs
None.

Mount options for smbfs
Just like nfs, the smb implementation expects a binary argument (a struct smb_mount_data) to the mount system call. This argument is constructed by smbmount(8) and the current version of mount (2.6c) does not know anything about smb.

Mount options for sysv
None.

Mount options for ufs
None.

Mount options for umsdos
See mount options for msdos. The dotsOK option is explicitly killed by umsdos.

Mount options for vfat
First of all, the mount options for fat are recognized. The dotsOK option is explicitly killed by vfat. Furthermore, there are

uni_xlate
    Translate unhandled Unicode characters to special escaped sequences. This lets you backup and restore filenames that are created with any Unicode characters. Without this option, a '?' is used when no translation is possible. The escape character is ':' because it is otherwise illegal on the vfat filesystem. The escape sequence that gets used, where u is the unicode character, is: ':', (u & 0x3f), ((u>>6) & 0x3f), (u>>12).

posix
    Allow two files with names that only differ in case.

nonumtail
    First try to make a short name without sequence number, before trying name~num.ext.

Mount options for xenix
None.

Mount options for xiafs
None. Although nothing is wrong with xiafs, it is not used much, and is not maintained. Probably one shouldn't use it. Since Linux version 2.1.21 xiafs is no longer part of the kernel source.

THE LOOP DEVICE
One further possible type is a mount via the loop device. For example, the command
  mount /tmp/fdimage /mnt -t msdos -o loop=/dev/loop3,blocksize=1024
will set up the loop device /dev/loop3 to correspond to the file /tmp/fdimage, and then mount this device on /mnt. This type of mount knows about three options, namely loop, offset and encryption, that are really options to losetup(8). If no explicit loop device is mentioned (but just an option `-o loop' is given), then mount will try to find some unused loop device and use that.

FILES
/etc/fstab file system table
/etc/mtab table of mounted file systems
/etc/mtab~ lock file
/etc/mtab.tmp temporary file

SEE ALSO
mount(2), umount(2), fstab(5), umount(8), swapon(8), nfs(5), mountd(8), nfsd(8), mke2fs(8), tune2fs(8), losetup(8)

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

Some Linux file systems don't support -o sync (the ext2fs does support synchronous updates (a la BSD) when mounted with the sync option).

The -o remount may not be able to change mount parameters (all ext2fs-specific parameters, except sb, are changeable with a remount, for example, but you can't change gid or umask for the fatfs).

HISTORY
A mount command appeared in Version 6 AT&T UNIX.