mount - mount a file system


mount [-lhV]

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

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

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


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.

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 file systems (of type type). The option -l adds the labels in this listing. See below.

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 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

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

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 It is possible to indicate a block special device using its volume LABEL or UUID (see the -L and -U options 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.)

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 file systems 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, it suffices to give only the device, or only the mount point.

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, 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 working with the loop device will be less convenient, and using the "user" option will fail.

The non-superuser mounts.

Normally, only the superuser can mount file systems. 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 file system found on his CDROM using the command

mount /dev/cdrom


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 full set of mount options used by an invocation of mount is determined by first extracting the mount 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.

Command line 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. The -f option checks for existing record in /etc/mtab and fails when the record already exists (with regular non-fake mount, this check is done by kernel).
-i 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 Mount without writing in /etc/mtab. This is necessary for example when /etc is on a read-only file system.
-p num In case of a loop mount with encryption, read the passphrase from file descriptor num instead of from the terminal.
-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.

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 Mount the file system 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.
-t vfstype
 The argument following the -t is used to indicate the file system type. The file system types which are currently supported include: adfs, affs, autofs, cifs, coda, coherent, cramfs, debugfs, devpts, efs, ext, ext2, ext3, ext4, hfs, hfsplus, hpfs, iso9660, jfs, minix, msdos, ncpfs, nfs, nfs4, ntfs, proc, qnx4, ramfs, reiserfs, romfs, smbfs, sysv, tmpfs, udf, ufs, umsdos, usbfs, vfat, xenix, xfs, xiafs. Note that coherent, sysv and xenix 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. Earlier, usbfs was known as usbdevfs. Note, the real list of all supported filesystems depends on your kernel.

For most types all the mount program has to do is issue a simple mount(2) system call, and no detailed knowledge of the filesystem type is required. For a few types however (like nfs, nfs4, cifs, smbfs, ncpfs) ad hoc code is necessary. The nfs, nfs4, cifs, smbfs, and ncpfs have a separate mount program. In order to make it possible to treat all types in a uniform way, mount will execute the program /sbin/mount.TYPE (if that exists) when called with type TYPE. Since various versions of the smbmount program have different calling conventions, /sbin/mount.smbfs may have to be a shell script that sets up the desired call.

If no -t option is given, or if the auto type is specified, mount will try to guess the desired type. Mount uses the blkid or volume_id library for guessing the filesystem type; if that does not turn up anything that looks familiar, mount will try to read the file /etc/filesystems, or, if that does not exist, /proc/filesystems. All of the filesystem types listed there will be tried, except for those that are labeled "nodev" (e.g., devpts, proc and nfs). If /etc/filesystems ends in a line with a single * only, mount will read /proc/filesystems afterwards.

The auto type may be useful for user-mounted floppies. Creating a file /etc/filesystems can be useful to change the probe order (e.g., to try vfat before msdos or ext3 before ext2) or if you use a kernel module autoloader. Warning: the probing uses a heuristic (the presence of appropriate ‘magic’), and could recognize the wrong filesystem type, possibly with catastrophic consequences. If your data is valuable, don’t ask mount to guess.

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 Used in conjunction with -a, to limit the set of filesystems to which the -a is applied. Like -t in this regard except that it is useless except in the context of -a. For example, the command:

mount -a -O no_netdev

mounts all file systems except those which have the option _netdev specified in the options field in the /etc/fstab file.

It is different from -t in that each option is matched exactly; a leading no at the beginning of one option does not negate the rest.

The -t and -O options are cumulative in effect; that is, the command

mount -a -t ext2 -O _netdev

mounts all ext2 filesystems with the _netdev option, not all filesystems that are either ext2 or have the _netdev option specified.

-o Options are specified with a -o flag followed by a comma separated string of options. For example:
  mount LABEL=mydisk -o noatime,nouser


-B, --bind Remount a subtree somewhere else (so that its contents are available in both places). See above.
-R, --rbind
 Remount a subtree and all possible submounts somewhere else (so that its contents are available in both places). See above.
-M, --move Move a subtree to some other place. See above.


Some of these options are only useful when they appear in the /etc/fstab file.

Some of these options could be enabled or disabled by default in the system kernel. To check the current setting see the options in /proc/mounts.

The following options apply to any file system that is being mounted (but not every file system actually honors them - e.g., the sync option today has effect only for ext2, ext3, fat, vfat and ufs):

async All I/O to the file system should be done asynchronously. (See also the sync option.)
atime Update inode access time for each access. This is the default.
 Do not update inode access times on this file system (e.g, for faster access on the news spool to speed up news servers).
auto Can be mounted with the -a option.
noauto Can only be mounted explicitly (i.e., the -a option will not cause the file system to be mounted).
context=context, fscontext=context, defcontext=context and rootcontext=context
 The context= option is useful when mounting filesystems that do not support extended attributes, such as a floppy or hard disk formatted with VFAT, or systems that are not normally running under SELinux, such as an ext3 formatted disk from a non-SELinux workstation. You can also use context= on filesystems you do not trust, such as a floppy. It also helps in compatibility with xattr-supporting filesystems on earlier 2.4.<x> kernel versions. Even where xattrs are supported, you can save time not having to label every file by assigning the entire disk one security context.

A commonly used option for removable media is context=system_u:object_r:removable_t.

Two other options are fscontext= and defcontext=, both of which are mutually exclusive of the context option. This means you can use fscontext and defcontext with each other, but neither can be used with context.

The fscontext= option works for all filesystems, regardless of their xattr support. The fscontext option sets the overarching filesystem label to a specific security context. This filesystem label is separate from the individual labels on the files. It represents the entire filesystem for certain kinds of permission checks, such as during mount or file creation. Individual file labels are still obtained from the xattrs on the files themselves. The context option actually sets the aggregate context that fscontext provides, in addition to supplying the same label for individual files.

You can set the default security context for unlabeled files using defcontext= option. This overrides the value set for unlabeled files in the policy and requires a file system that supports xattr labeling.

The rootcontext= option allows you to explicitly label the root inode of a FS being mounted before that FS or inode because visable to userspace. This was found to be useful for things like stateless linux.

For more details, see selinux(8)

 Use default options: rw, suid, dev, exec, auto, nouser, and async.
dev Interpret character or block special devices on the file system.
nodev Do not interpret character or block special devices on the file system.
 Update directory inode access times on this filesystem. This is the default.
 Do not update directory inode access times on this filesystem.
 All directory updates within the file system should be done synchronously. This affects the following system calls: creat, link, unlink, symlink, mkdir, rmdir, mknod and rename.
exec Permit execution of binaries.
noexec Do not allow direct execution of any binaries on the mounted file system. (Until recently it was possible to run binaries anyway using a command like /lib/ld*.so /mnt/binary. This trick fails since Linux 2.4.25 / 2.6.0.)
group Allow an ordinary (i.e., non-root) user to mount the file system if one of his groups matches the group of the device. This option implies the options nosuid and nodev (unless overridden by subsequent options, as in the option line group,dev,suid).
 Every time the inode is modified, the i_version field will be incremented.
 Do not increment the i_version inode field.
 Specifies an encryption algorithm to use. Used in conjunction with the loop option.
 Specifies the key size to use for an encryption algorithm. Used in conjunction with the loop and encryption options.
mand Allow mandatory locks on this filesystem. See fcntl(2).
nomand Do not allow mandatory locks on this filesystem.
 The filesystem resides on a device that requires network access (used to prevent the system from attempting to mount these filesystems until the network has been enabled on the system).
nofail Do not report errors for this device if it does not exist.
 Update inode access times relative to modify or change time. Access time is only updated if the previous access time was earlier than the current modify or change time. (Similar to noatime, but doesn’t break mutt or other applications that need to know if a file has been read since the last time it was modified.)
 Do not use relatime feature (e.g, for systems where the feature is enabled by default, for more details see mount options in /proc/mounts).
 Update inode access times whenever a file is accessed. Disables noatime and relatime.
 Use the kernel’s default behaviour for inode access time updates.
suid Allow set-user-identifier or set-group-identifier bits to take effect.
nosuid Do not allow set-user-identifier or set-group-identifier bits to take effect. (This seems safe, but is in fact rather unsafe if you have suidperl(1) installed.)
owner Allow an ordinary (i.e., non-root) user to mount the file system if he is the owner of the device. This option implies the options nosuid and nodev (unless overridden by subsequent options, as in the option line owner,dev,suid).
 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. It does not change device or mount point.

The remount functionality follows the standard way how the mount command works with options from fstab. It means the mount command doesn’t read fstab (or mtab) only when a device and dir are fully specified.

mount -o remount,rw /dev/foo /dir

After this call all old mount options are replaced and arbitrary stuff from fstab is ignored, except the loop= option which is internally generated and maintained by the mount command.

mount -o remount,rw /dir

After this call mount reads fstab (or mtab) and merges these options with options from command line ( -o ).

ro Mount the file system read-only.
rw Mount the file system read-write.
sync All I/O to the file system should be done synchronously. In case of media with limited number of write cycles (e.g. some flash drives) "sync" may cause life-cycle shortening.
user Allow an ordinary user to mount the file system. The name of the mounting user is written to mtab so that he can unmount the file system again. This option implies the options noexec, nosuid, and nodev (unless overridden by subsequent options, as in the option line user,exec,dev,suid).
nouser Forbid an ordinary (i.e., non-root) user to mount the file system. This is the default.
users Allow every user to mount and unmount the file system. This option implies the options noexec, nosuid, and nodev (unless overridden by subsequent options, as in the option line users,exec,dev,suid).


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

What options are supported depends a bit on the running kernel. More info may be found in the kernel source subdirectory Documentation/filesystems.

Mount options for adfs

uid=value and gid=value
 Set the owner and group of the files in the file system (default: uid=gid=0).
ownmask=value and othmask=value
 Set the permission mask for ADFS ’owner’ permissions and ’other’ permissions, respectively (default: 0700 and 0077, respectively). See also /usr/src/linux/Documentation/filesystems/adfs.txt.

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.
 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.
 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...
 Print an informational message for each successful mount.
 Prefix used before volume name, when following a link.
 Prefix (of length at most 30) used before ’/’ when following a symbolic link.
 (Default: 2.) Number of unused blocks at the start of the device.
 Give explicitly the location of the root block.
 Give blocksize. Allowed values are 512, 1024, 2048, 4096.
grpquota / noquota / quota / usrquota
 These options are accepted but ignored. (However, quota utilities may react to such strings in /etc/fstab.)

Mount options for cifs

See the options section of the mount.cifs(8) man page (cifs-mount package must be installed).

Mount options for coherent


Mount options for debugfs

The debugfs file system is a pseudo file system, traditionally mounted on /sys/kernel/debug. There are no mount options.

Mount options for devpts

The devpts file system is a pseudo file system, traditionally mounted on /dev/pts. In order to acquire a pseudo terminal, a process opens /dev/ptmx; the number of the pseudo terminal is then made available to the process and the pseudo terminal slave can be accessed as /dev/pts/<number>.
uid=value and gid=value
 This sets the owner or the group of newly created PTYs to the specified values. When nothing is specified, they will be set to the UID and GID of the creating process. For example, if there is a tty group with GID 5, then gid=5 will cause newly created PTYs to belong to the tty group.
 Set the mode of newly created PTYs to the specified value. The default is 0600. A value of mode=620 and gid=5 makes "mesg y" the default on newly created PTYs.
 Create a private instance of devpts filesystem, such that indices of ptys allocated in this new instance are independent of indices created in other instances of devpts.

All mounts of devpts without this newinstance option share the same set of pty indices (i.e legacy mode). Each mount of devpts with the newinstance option has a private set of pty indices.

This option is mainly used to support containers in the linux kernel. It is implemented in linux kernel versions starting with 2.6.29. Further, this mount option is valid only if CONFIG_DEVPTS_MULTIPLE_INSTANCES is enabled in the kernel configuration.

To use this option effectively, /dev/ptmx must be a symbolic link to pts/ptmx. See Documentation/filesystems/devpts.txt in the linux kernel source tree for details.


Set the mode for the new ptmx device node in the devpts filesystem.

With the support for multiple instances of devpts (see newinstance option above), each instance has a private ptmx node in the root of the devpts filesystem (typically /dev/pts/ptmx).

For compatibility with older versions of the kernel, the default mode of the new ptmx node is 0000. ptmxmode=value specifies a more useful mode for the ptmx node and is highly recommended when the newinstance option is specified.

This option is only implemented in linux kernel versions starting with 2.6.29. Further this option is valid only if CONFIG_DEVPTS_MULTIPLE_INSTANCES is enabled in the kernel configuration.

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. Since Linux 2.5.46, for most mount options the default is determined by the filesystem superblock. Set them with tune2fs(8).
acl / noacl
 Support POSIX Access Control Lists (or not).
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=none / nocheck
 No checking is done at mount time. This is the default. This is fast. It is wise to invoke e2fsck(8) every now and then, e.g. at boot time.
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.
grpquota / noquota / quota / usrquota
 These options are accepted but ignored.
nobh Do not attach buffer_heads to file pagecache. (Since 2.5.49.)
 Disables 32-bit UIDs and GIDs. This is for interoperability with older kernels which only store and expect 16-bit values.
oldalloc or orlov
 Use old allocator or Orlov allocator for new inodes. Orlov is default.
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. (Earlier, copies of the superblock would be made every 8192 blocks: in block 1, 8193, 16385, ... (and one got thousands of copies on a big filesystem). Since version 1.08, mke2fs has a -s (sparse superblock) option to reduce the number of backup superblocks, and since version 1.15 this is the default. Note that this may mean that ext2 filesystems created by a recent mke2fs cannot be mounted r/w under Linux 2.0.*.) The block number here uses 1k units. Thus, if you want to use logical block 32768 on a filesystem with 4k blocks, use "sb=131072".
user_xattr / nouser_xattr
 Support "user." extended attributes (or not).

Mount options for ext3

The ‘ext3’ file system is a version of the ext2 file system which has been enhanced with journalling. It supports the same options as ext2 as well as the following additions:
 Update the ext3 file system’s journal to the current format.
 When a journal already exists, this option is ignored. Otherwise, it specifies the number of the inode which will represent the ext3 file system’s journal file; ext3 will create a new journal, overwriting the old contents of the file whose inode number is inum.
noload Do not load the ext3 file system’s journal on mounting.
data=journal / data=ordered / data=writeback
 Specifies the journalling mode for file data. Metadata is always journaled. To use modes other than ordered on the root file system, pass the mode to the kernel as boot parameter, e.g. rootflags=data=journal.
 All data is committed into the journal prior to being written into the main file system.
 This is the default mode. All data is forced directly out to the main file system prior to its metadata being committed to the journal.
 Data ordering is not preserved - data may be written into the main file system after its metadata has been committed to the journal. This is rumoured to be the highest-throughput option. It guarantees internal file system integrity, however it can allow old data to appear in files after a crash and journal recovery.
 Sync all data and metadata every nrsec seconds. The default value is 5 seconds. Zero means default.
 Enable Extended User Attributes. See the attr(5) manual page.
acl Enable POSIX Access Control Lists. See the acl(5) manual page.

Mount options for ext4

The ‘ext4’ is an an advanced level of the ext3 filesystem which incorporates scalability and reliability enhancements for supporting large filesystem.

The options journal_dev, noload, data, commit, orlov, oldalloc, [no]user_xattr [no]acl, bsddf, minixdf, debug, errors, data_err, grpid, bsdgroups, nogrpid sysvgroups, resgid, resuid, sb, quota, noquota, grpquota, usrquota and [no]bh are backwardly compatible with ext3 or ext2.
 Enable checksumming of the journal transactions. This will allow the recovery code in e2fsck and the kernel to detect corruption in the kernel. It is a compatible change and will be ignored by older kernels.
 Commit block can be written to disk without waiting for descriptor blocks. If enabled older kernels cannot mount the device. This will enable
 Update the ext4 file system’s journal to the current format.
barrier=0 / barrier=1 / barrier / nobarrier
 This enables/disables the use of write barriers in the jbd code. barrier=0 disables, barrier=1 enables. This also requires an IO stack which can support barriers, and if jbd gets an error on a barrier write, it will disable again with a warning. Write barriers enforce proper on-disk ordering of journal commits, making volatile disk write caches safe to use, at some performance penalty. If your disks are battery-backed in one way or another, disabling barriers may safely improve performance. The mount options "barrier" and "nobarrier" can also be used to enable or disable barriers, for consistency with other ext4 mount options.
 This tuning parameter controls the maximum number of inode table blocks that ext4’s inode table readahead algorithm will pre-read into the buffer cache. The default value is 32 blocks.
 Number of filesystem blocks that mballoc will try to use for allocation size and alignment. For RAID5/6 systems this should be the number of data disks * RAID chunk size in file system blocks.
 Deferring block allocation until write-out time.
 Disable delayed allocation. Blocks are allocation when data is copied from user to page cache.
 Maximum amount of time ext4 should wait for additional filesystem operations to be batch together with a synchronous write operation. Since a synchronous write operation is going to force a commit and then a wait for the I/O complete, it doesn’t cost much, and can be a huge throughput win, we wait for a small amount of time to see if any other transactions can piggyback on the synchronous write. The algorithm used is designed to automatically tune for the speed of the disk, by measuring the amount of time (on average) that it takes to finish committing a transaction. Call this time the "commit time". If the time that the transactoin has been running is less than the commit time, ext4 will try sleeping for the commit time to see if other operations will join the transaction. The commit time is capped by the max_batch_time, which defaults to 15000us (15ms). This optimization can be turned off entirely by setting max_batch_time to 0.
 This parameter sets the commit time (as described above) to be at least min_batch_time. It defaults to zero microseconds. Increasing this parameter may improve the throughput of multi-threaded, synchronous workloads on very fast disks, at the cost of increasing latency.
 The I/O priority (from 0 to 7, where 0 is the highest priorty) which should be used for I/O operations submitted by kjournald2 during a commit operation. This defaults to 3, which is a slightly higher priority than the default I/O priority.
auto_da_alloc / noauto_da_alloc
 Many broken applications don’t use fsync() when noauto_da_alloc replacing existing files via patterns such as

fd = open("")/write(fd,..)/close(fd)/ rename("", "foo")

or worse yet

fd = open("foo", O_TRUNC)/write(fd,..)/close(fd).

If auto_da_alloc is enabled, ext4 will detect the replace-via-rename and replace-via-truncate patterns and force that any delayed allocation blocks are allocated such that at the next journal commit, in the default data=ordered mode, the data blocks of the new file are forced to disk before the rename() operation is commited. This provides roughly the same level of guarantees as ext3, and avoids the "zero-length" problem that can happen when a system crashes before the delayed allocation blocks are forced to disk.

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 / blocksize=2048
 Set blocksize (default 512). This option is obsolete.
uid=value and gid=value
 Set the owner and group of all files. (Default: the uid and gid of the current process.)
 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.
 Set the umask applied to directories only. The default is the umask of the current process. The value is given in octal.
 Set the umask applied to regular files only. The default is the umask of the current process. The value is given in octal.
 This option controls the permission check of mtime/atime.
20 If current process is in group of file’s group ID, you can change timestamp.
2 Other users can change timestamp.
The default is set from ‘dmask’ option. (If the directory is writable, utime(2) is also allowed. I.e. ~dmask & 022)

Normally utime(2) checks current process is owner of the file, or it has CAP_FOWNER capability. But FAT filesystem doesn’t have uid/gid on disk, so normal check is too unflexible. With this option you can relax it.

 Three different levels of pickyness can be chosen:
 Upper and lower case are accepted and equivalent, long name parts are truncated (e.g. verylongname.foobar becomes, leading and embedded spaces are accepted in each name part (name and extension).
 Like "relaxed", but many special characters (*, ?, <, spaces, etc.) are rejected. This is the default.
 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.)
 Sets the codepage for converting to shortname characters on FAT and VFAT filesystems. By default, codepage 437 is used.
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. This option is obsolete.

 Forces the driver to use the CVF (Compressed Volume File) module cvf_module instead of auto-detection. If the kernel supports kmod, the cvf_format=xxx option also controls on-demand CVF module loading. This option is obsolete.
 Option passed to the CVF module. This option is obsolete.
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 / fat=32
 Specify a 12, 16 or 32 bit fat. This overrides the automatic FAT type detection routine. Use with caution!
 Character set to use for converting between 8 bit characters and 16 bit Unicode characters. The default is iso8859-1. Long filenames are stored on disk in Unicode format.
tz=UTC This option disables the conversion of timestamps between local time (as used by Windows on FAT) and UTC (which Linux uses internally). This is particuluarly useful when mounting devices (like digital cameras) that are set to UTC in order to avoid the pitfalls of local time.
quiet Turn on the quiet flag. Attempts to chown or chmod files do not return errors, although they fail. Use with caution!
 If set, the execute permission bits of the file will be allowed only if the extension part of the name is .EXE, .COM, or .BAT. Not set by default.
 If set, ATTR_SYS attribute on FAT is handled as IMMUTABLE flag on Linux. Not set by default.
flush If set, the filesystem will try to flush to disk more early than normal. Not set by default.
 Use the "free clusters" value stored on FSINFO. It’ll be used to determine number of free clusters without scanning disk. But it’s not used by default, because recent Windows don’t update it correctly in some case. If you are sure the "free clusters" on FSINFO is correct, by this option you can avoid scanning disk.
dots, nodots, dotsOK=[yes|no]
 Various misguided attempts to force Unix or DOS conventions onto a FAT file system.

Mount options for hfs

creator=cccc, type=cccc
 Set the creator/type values as shown by the MacOS finder used for creating new files. Default values: ’????’.
uid=n, gid=n
 Set the owner and group of all files. (Default: the uid and gid of the current process.)
dir_umask=n, file_umask=n, umask=n
 Set the umask used for all directories, all regular files, or all files and directories. Defaults to the umask of the current process.
 Select the CDROM session to mount. Defaults to leaving that decision to the CDROM driver. This option will fail with anything but a CDROM as underlying device.
 Select partition number n from the device. Only makes sense for CDROMS. Defaults to not parsing the partition table at all.
quiet Don’t complain about invalid mount options.

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.)
 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.
 Do not abort mounting when certain consistency checks fail.

Mount options for iso9660

ISO 9660 is a standard describing a filesystem structure to be used on CD-ROMs. (This filesystem type is also seen on some DVDs. See also the udf filesystem.)

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.
 Disable the use of Microsoft Joliet 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] / map=a[corn]
 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.) map=acorn is like map=normal but also apply Acorn extensions if present.
 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. (If the ordinary files and the associated or hidden files have the same filenames, this may make the ordinary files inaccessible.)
 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, possibly 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.
 Select number of session on multisession CD. (Since 2.3.4.)
 Session begins from sector xxx. (Since 2.3.4.)
The following options are the same as for vfat and specifying them only makes sense when using discs encoded using Microsoft’s Joliet extensions.
 Character set to use for converting 16 bit Unicode characters on CD to 8 bit characters. The default is iso8859-1.
utf8 Convert 16 bit Unicode characters on CD to UTF-8.

Mount options for jfs

 Character set to use for converting from Unicode to ASCII. The default is to do no conversion. Use iocharset=utf8 for UTF8 translations. This requires CONFIG_NLS_UTF8 to be set in the kernel .config file.
 Resize the volume to value blocks. JFS only supports growing a volume, not shrinking it. This option is only valid during a remount, when the volume is mounted read-write. The resize keyword with no value will grow the volume to the full size of the partition.
 Do not write to the journal. The primary use of this option is to allow for higher performance when restoring a volume from backup media. The integrity of the volume is not guaranteed if the system abnormally abends.
 Default. Commit metadata changes to the journal. Use this option to remount a volume where the nointegrity option was previously specified in order to restore normal behavior.
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.)
noquota / quota / usrquota / grpquota
 These options are accepted but ignored.

Mount options for minix


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 ncpfs

Just like nfs, the ncpfs 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 (2.12) does not know anything about ncpfs.

Mount options for nfs and nfs4

See the options section of the nfs(5) man page (nfs-utils package must be installed).

The nfs and nfs4 implementation expects a binary argument (a struct nfs_mount_data) to the mount system call. This argument is constructed by mount.nfs(8) and the current version of mount (2.13) does not know anything about nfs and nfs4.

Mount options for ntfs

 Character set to use when returning file names. Unlike VFAT, NTFS suppresses names that contain unconvertible characters. Deprecated.
 New name for the option earlier called iocharset.
utf8 Use UTF-8 for converting file names.
 For 0 (or ‘no’ or ‘false’), do not use escape sequences for unknown Unicode characters. For 1 (or ‘yes’ or ‘true’) or 2, use vfat-style 4-byte escape sequences starting with ":". Here 2 give a little-endian encoding and 1 a byteswapped bigendian encoding.
 If enabled (posix=1), the file system distinguishes between upper and lower case. The 8.3 alias names are presented as hard links instead of being suppressed. This option is obsolete.
uid=value, gid=value and umask=value
 Set the file permission on the filesystem. The umask value is given in octal. By default, the files are owned by root and not readable by somebody else.

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 ramfs

Ramfs is a memory based filesystem. Mount it and you have it. Unmount it and it is gone. Present since Linux 2.3.99pre4. There are no mount options.

Mount options for reiserfs

Reiserfs is a journaling filesystem.
conv Instructs version 3.6 reiserfs software to mount a version 3.5 file system, using the 3.6 format for newly created objects. This file system will no longer be compatible with reiserfs 3.5 tools.
hash=rupasov / hash=tea / hash=r5 / hash=detect
 Choose which hash function reiserfs will use to find files within directories.
 A hash invented by Yury Yu. Rupasov. It is fast and preserves locality, mapping lexicographically close file names to close hash values. This option should not be used, as it causes a high probability of hash collisions.
tea A Davis-Meyer function implemented by Jeremy Fitzhardinge. It uses hash permuting bits in the name. It gets high randomness and, therefore, low probability of hash collisions at some CPU cost. This may be used if EHASHCOLLISION errors are experienced with the r5 hash.
r5 A modified version of the rupasov hash. It is used by default and is the best choice unless the file system has huge directories and unusual file-name patterns.
detect Instructs mount to detect which hash function is in use by examining the file system being mounted, and to write this information into the reiserfs superblock. This is only useful on the first mount of an old format file system.
 Tunes the block allocator. This may provide performance improvements in some situations.
 Tunes the block allocator. This may provide performance improvements in some situations.
 Disable the border allocator algorithm invented by Yury Yu. Rupasov. This may provide performance improvements in some situations.
nolog Disable journalling. This will provide slight performance improvements in some situations at the cost of losing reiserfs’s fast recovery from crashes. Even with this option turned on, reiserfs still performs all journalling operations, save for actual writes into its journalling area. Implementation of nolog is a work in progress.
notail By default, reiserfs stores small files and ‘file tails’ directly into its tree. This confuses some utilities such as LILO(8) . This option is used to disable packing of files into the tree.
 Replay the transactions which are in the journal, but do not actually mount the file system. Mainly used by reiserfsck.
 A remount option which permits online expansion of reiserfs partitions. Instructs reiserfs to assume that the device has number blocks. This option is designed for use with devices which are under logical volume management (LVM). There is a special resizer utility which can be obtained from
 Enable Extended User Attributes. See the attr(5) manual page.
acl Enable POSIX Access Control Lists. See the acl(5) manual page.

Mount options for romfs


Mount options for smbfs

Just like nfs, the smbfs 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 (2.12) does not know anything about smbfs.

Mount options for sysv


Mount options for tmpfs

 Override default maximum size of the filesystem. The size is given in bytes, and rounded down to entire pages. The default is half of the memory. The size parameter also accepts a suffix % to limit this tmpfs instance to that percentage of your physical RAM: the default, when neither size nor nr_blocks is specified, is size=50%
 The same as size, but in blocks of PAGE_CACHE_SIZE
 The maximum number of inodes for this instance. The default is half of the number of your physical RAM pages, or (on a machine with highmem) the number of lowmem RAM pages, whichever is the lower.
The tmpfs mount options for sizing ( size, nr_blocks, and nr_inodes) accept a suffix k, m or g for Ki, Mi, Gi (binary kilo, mega and giga) and can be changed on remount.

mode= Set initial permissions of the root directory.
uid= The user id.
gid= The group id.
 Set the NUMA memory allocation policy for all files in that instance (if the kernel CONFIG_NUMA is enabled) - which can be adjusted on the fly via ’mount -o remount ...’
 prefers to allocate memory from the local node
 prefers to allocate memory from the given Node
 allocates memory only from nodes in NodeList
 prefers to allocate from each node in turn
 allocates from each node of NodeList in turn.
The NodeList format is a comma-separated list of decimal numbers and ranges, a range being two hyphen-separated decimal numbers, the smallest and largest node numbers in the range. For example, mpol=bind:0-3,5,7,9-15

Note that trying to mount a tmpfs with an mpol option will fail if the running kernel does not support NUMA; and will fail if its nodelist specifies a node which is not online. If your system relies on that tmpfs being mounted, but from time to time runs a kernel built without NUMA capability (perhaps a safe recovery kernel), or with fewer nodes online, then it is advisable to omit the mpol option from automatic mount options. It can be added later, when the tmpfs is already mounted on MountPoint, by ’mount -o remount,mpol=Policy:NodeList MountPoint’.

Mount options for udf

udf is the "Universal Disk Format" filesystem defined by the Optical Storage Technology Association, and is often used for DVD-ROM. See also iso9660.
gid= Set the default group.
umask= Set the default umask. The value is given in octal.
uid= Set the default user.
unhide Show otherwise hidden files.
 Show deleted files in lists.
 Unset strict conformance.
 Set the NLS character set.
bs= Set the block size. (May not work unless 2048.)
novrs Skip volume sequence recognition.
 Set the CDROM session counting from 0. Default: last session.
 Override standard anchor location. Default: 256.
 Override the VolumeDesc location. (unused)
 Override the PartitionDesc location. (unused)
 Set the last block of the filesystem.
 Override the fileset block location. (unused)
 Override the root directory location. (unused)

Mount options for ufs

 UFS is a file system widely used in different operating systems. The problem are differences among implementations. Features of some implementations are undocumented, so its hard to recognize the type of ufs automatically. That’s why the user must specify the type of ufs by mount option. Possible values are:
old Old format of ufs, this is the default, read only. (Don’t forget to give the -r option.)
44bsd For filesystems created by a BSD-like system (NetBSD,FreeBSD,OpenBSD).
sun For filesystems created by SunOS or Solaris on Sparc.
sunx86 For filesystems created by Solaris on x86.
hp For filesystems created by HP-UX, read-only.
 For filesystems created by NeXTStep (on NeXT station) (currently read only).
 For NextStep CDROMs (block_size == 2048), read-only.
 For filesystems created by OpenStep (currently read only). The same filesystem type is also used by Mac OS X.

 Set behaviour on error:
panic If an error is encountered, cause a kernel panic.
 These mount options don’t do anything at present; when an error is encountered only a console message is printed.

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
 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.
 First try to make a short name without sequence number, before trying name~num.ext.
utf8 UTF8 is the filesystem safe 8-bit encoding of Unicode that is used by the console. It can be be enabled for the filesystem with this option or disabled with utf8=0, utf8=no or utf8=false. If ‘uni_xlate’ gets set, UTF8 gets disabled.

Defines the behaviour for creation and display of filenames which fit into 8.3 characters. If a long name for a file exists, it will always be preferred display. There are four modes: :
lower Force the short name to lower case upon display; store a long name when the short name is not all upper case. This mode is the default.
win95 Force the short name to upper case upon display; store a long name when the short name is not all upper case.
winnt Display the shortname as is; store a long name when the short name is not all lower case or all upper case.
mixed Display the short name as is; store a long name when the short name is not all upper case.

Mount options for usbfs

devuid=uid and devgid=gid and devmode=mode
 Set the owner and group and mode of the device files in the usbfs file system (default: uid=gid=0, mode=0644). The mode is given in octal.
busuid=uid and busgid=gid and busmode=mode
 Set the owner and group and mode of the bus directories in the usbfs file system (default: uid=gid=0, mode=0555). The mode is given in octal.
listuid=uid and listgid=gid and listmode=mode
 Set the owner and group and mode of the file devices (default: uid=gid=0, mode=0444). The mode is given in octal.

Mount options for xenix


Mount options for xfs

 Sets the buffered I/O end-of-file preallocation size when doing delayed allocation writeout (default size is 64KiB). Valid values for this option are page size (typically 4KiB) through to 1GiB, inclusive, in power-of-2 increments.
attr2 / noattr2
 The options enable/disable (default is disabled for backward compatibility on-disk) an "opportunistic" improvement to be made in the way inline extended attributes are stored on-disk. When the new form is used for the first time (by setting or removing extended attributes) the on-disk superblock feature bit field will be updated to reflect this format being in use.
 Enables the use of block layer write barriers for writes into the journal and unwritten extent conversion. This allows for drive level write caching to be enabled, for devices that support write barriers.
dmapi Enable the DMAPI (Data Management API) event callouts. Use with the mtpt option.
grpid / bsdgroups and nogrpid / 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.
 Sets the number of hash buckets available for hashing the in-memory inodes of the specified mount point. If a value of zero is used, the value selected by the default algorithm will be displayed in /proc/mounts.
ikeep / noikeep
 When inode clusters are emptied of inodes, keep them around on the disk (ikeep) - this is the traditional XFS behaviour and is still the default for now. Using the noikeep option, inode clusters are returned to the free space pool.
 Indicates that XFS is allowed to create inodes at any location in the filesystem, including those which will result in inode numbers occupying more than 32 bits of significance. This is provided for backwards compatibility, but causes problems for backup applications that cannot handle large inode numbers.
largeio / nolargeio
 If nolargeio is specified, the optimal I/O reported in st_blksize by stat(2) will be as small as possible to allow user applications to avoid inefficient read/modify/write I/O. If largeio is specified, a filesystem that has a swidth specified will return the swidth value (in bytes) in st_blksize. If the filesystem does not have a swidth specified but does specify an allocsize then allocsize (in bytes) will be returned instead. If neither of these two options are specified, then filesystem will behave as if nolargeio was specified.
 Set the number of in-memory log buffers. Valid numbers range from 2-8 inclusive. The default value is 8 buffers for filesystems with a blocksize of 64KiB, 4 buffers for filesystems with a blocksize of 32KiB, 3 buffers for filesystems with a blocksize of 16KiB and 2 buffers for all other configurations. Increasing the number of buffers may increase performance on some workloads at the cost of the memory used for the additional log buffers and their associated control structures.
 Set the size of each in-memory log buffer. Size may be specified in bytes, or in kilobytes with a "k" suffix. Valid sizes for version 1 and version 2 logs are 16384 (16k) and 32768 (32k). Valid sizes for version 2 logs also include 65536 (64k), 131072 (128k) and 262144 (256k). The default value for machines with more than 32MiB of memory is 32768, machines with less memory use 16384 by default.
logdev=device and rtdev=device
 Use an external log (metadata journal) and/or real-time device. An XFS filesystem has up to three parts: a data section, a log section, and a real-time section. The real-time section is optional, and the log section can be separate from the data section or contained within it. Refer to xfs(5).
 Use with the dmapi option. The value specified here will be included in the DMAPI mount event, and should be the path of the actual mountpoint that is used.
 Data allocations will not be aligned at stripe unit boundaries.
 Access timestamps are not updated when a file is read.
 The filesystem will be mounted without running log recovery. If the filesystem was not cleanly unmounted, it is likely to be inconsistent when mounted in norecovery mode. Some files or directories may not be accessible because of this. Filesystems mounted norecovery must be mounted read-only or the mount will fail.
nouuid Don’t check for double mounted file systems using the file system uuid. This is useful to mount LVM snapshot volumes.
 Make O_SYNC writes implement true O_SYNC. WITHOUT this option, Linux XFS behaves as if an osyncisdsync option is used, which will make writes to files opened with the O_SYNC flag set behave as if the O_DSYNC flag had been used instead. This can result in better performance without compromising data safety. However if this option is not in effect, timestamp updates from O_SYNC writes can be lost if the system crashes. If timestamp updates are critical, use the osyncisosync option.
uquota / usrquota / uqnoenforce / quota
 User disk quota accounting enabled, and limits (optionally) enforced. Refer to xfs_quota(8) for further details.
gquota / grpquota / gqnoenforce
 Group disk quota accounting enabled and limits (optionally) enforced. Refer to xfs_quota(8) for further details.
pquota / prjquota / pqnoenforce
 Project disk quota accounting enabled and limits (optionally) enforced. Refer to xfs_quota(8) for further details.
sunit=value and swidth=value
 Used to specify the stripe unit and width for a RAID device or a stripe volume. value must be specified in 512-byte block units. If this option is not specified and the filesystem was made on a stripe volume or the stripe width or unit were specified for the RAID device at mkfs time, then the mount system call will restore the value from the superblock. For filesystems that are made directly on RAID devices, these options can be used to override the information in the superblock if the underlying disk layout changes after the filesystem has been created. The swidth option is required if the sunit option has been specified, and must be a multiple of the sunit value.
 Data allocations will be rounded up to stripe width boundaries when the current end of file is being extended and the file size is larger than the stripe width size.

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.


One further possible type is a mount via the loop device. For example, the command

mount /tmp/fdimage /mnt -t vfat -o loop=/dev/loop3

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 four options, namely loop, offset, sizelimit and encryption, that are really options to  losetup(8). (These options can be used in addition to those specific to the filesystem type.) If the mount requires a passphrase, you will be prompted for one unless you specify a file descriptor to read from instead with the --pass-fd option.

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.

Since Linux 2.6.25 is supported auto-destruction of loop devices and then any loop device allocated by mount will be freed by umount independently on /etc/mtab .

You can also free a loop device by hand, using ‘losetup -d’ or ‘umount -d‘.


mount has the following return codes (the bits can be ORed):
0 success
1 incorrect invocation or permissions
2 system error (out of memory, cannot fork, no more loop devices)
4 internal mount bug
8 user interrupt
16 problems writing or locking /etc/mtab
32 mount failure
64 some mount succeeded


The syntax of external mount helpers is:

/sbin/mount.<suffix> spec dir [-sfnv] [-o options]

where the <suffix> is filesystem type and -sfnvo options have same meaning like standard mount options.


/etc/fstab file system table
/etc/mtab table of mounted file systems
/etc/mtab~ lock file
/etc/mtab.tmp temporary file
/etc/filesystems a list of filesystem types to try


mount(2), umount(2), fstab(5), umount(8), swapon(8), nfs(5), xfs(5), e2label(8), xfs_admin(8), mountd(8), nfsd(8), mke2fs(8), tune2fs(8), losetup(8)


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

Some Linux file systems don’t support -o sync and -o dirsync (the ext2, ext3, fat and vfat file systems do 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).

Mount by label or uuid will work only if your devices have the names listed in /proc/partitions. In particular, it may well fail if the kernel was compiled with devfs but devfs is not mounted.

It is possible that files /etc/mtab and /proc/mounts don’t match. The first file is based only on the mount command options, but the content of the second file also depends on the kernel and others settings (e.g. remote NFS server. In particular case the mount command may reports unreliable information about a NFS mount point and the /proc/mounts file usually contains more reliable information.)

Checking files on NFS filesystem referenced by file descriptors (i.e. the fcntl and ioctl families of functions) may lead to inconsistent result due to the lack of consistency check in kernel even if noac is used.


A mount command existed in Version 5 AT&T UNIX.


The mount command is part of the util-linux-ng package and is available from

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