Display version information and exit.

Display help text and exit.

Verbose mode.

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

(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.

Causes everything to be done except for the actual system call; if it's not obvious, this ``fakes'' mounting the filesystem. 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).

Don't call the /sbin/mount.<filesystem> helper even if it exists.

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).

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

Don't canonicalize paths. The mount command canonicalizes all paths (from command line or fstab) and stores canonicalized paths to the /etc/mtab file. This option can be used together with the −f flag for already canonicalized absolute paths.

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.

If only one argument for the mount command is given then the argument might be interpreted as target (mountpoint) or source (device). This option allows to explicitly define that the argument is mount source.

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).

Mount the filesystem read/write. This is the default. A synonym is −o rw.

Mount the partition that has the specified label.

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

Specifies alternative fstab file. If the path is directory then the files in the directory are sorted by strverscmp(3), files that starts with "." or without .fstab extension are ignored. The option can be specified more than once. This option is mostly designed for initramfs or chroot scripts where additional configuration is specified outside standard system configuration.

Note that mount(8) does not pass the option −−fstab to /sbin/mount.<type> helpers, it means that the alternative fstab files will be invisible for the helpers. This is no problem for normal mounts, but user (non-root) mounts always require fstab to verify user's rights.

The argument following the −t is used to indicate the filesystem type. The filesystem 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, squashfs, smbfs, sysv, tmpfs, ubifs, 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.

The programs mount and umount support filesystem subtypes. The subtype is defined by '.subtype' suffix. For example 'fuse.sshfs'. It's recommended to use subtype notation rather than add any prefix to the mount source (for example 'sshfs#example.com' is deprecated).

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 filesystems 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 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. All of the filesystem types will be mounted with mount option "silent".

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.

More than one type may be specified in a comma separated list. The list of filesystem types can be prefixed with no to specify the filesystem types on which no action should be taken. (This can be meaningful with the −a option.) For example, the command:

If only one argument for the mount command is given then the argument might be interpreted as target (mountpoint) or source (device). This option allows to explicitly define that the argument is mount target.

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:

Options are specified with a −o flag followed by a comma separated string of options. For example:

Remount a subtree somewhere else (so that its contents are available in both places). See above.

Remount a subtree and all possible submounts somewhere else (so that its contents are available in both places). See above.

Move a subtree to some other place. See above.

All I/O to the filesystem should be done asynchronously. (See also the sync option.)

Do not use noatime feature, then the inode access time is controlled by kernel defaults. See also the description for strictatime and relatime mount options.

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

Can be mounted with the −a option.

Can only be mounted explicitly (i.e., the −a option will not cause the filesystem to be mounted).

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 filesystem 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 becomes visible to userspace. This was found to be useful for things like stateless linux.

Note that the kernel rejects any remount request that includes the context option, even when unchanged from the current context.

Warning: the context value might contain commas, in which case the value has to be properly quoted, otherwise mount(8) will interpret the comma as a separator between mount options. Don't forget that the shell strips off quotes and thus double quoting is required. For example:

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

Interpret character or block special devices on the filesystem.

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 filesystem should be done synchronously. This affects the following system calls: creat, link, unlink, symlink, mkdir, rmdir, mknod and rename.

Permit execution of binaries.

Do not allow direct execution of any binaries on the mounted filesystem. (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.)

Allow an ordinary (i.e., non-root) user to mount the filesystem 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.

Allow mandatory locks on this filesystem. See fcntl(2).

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).

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.)

Since Linux 2.6.30, the kernel defaults to the behavior provided by this option (unless noatime was specified), and the strictatime option is required to obtain traditional semantics. In addition, since Linux 2.6.30, the file's last access time is always updated if it is more than 1 day old.

Do not use relatime feature. See also the strictatime mount option.

Allows to explicitly requesting full atime updates. This makes it possible for kernel to defaults to relatime or noatime but still allow userspace to override it. For more details about the default system mount options see /proc/mounts.

Use the kernel's default behaviour for inode access time updates.

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

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.)

Turn on the silent flag.

Turn off the silent flag.

Allow an ordinary (i.e., non-root) user to mount the filesystem 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 filesystem. This is commonly used to change the mount flags for a filesystem, especially to make a readonly filesystem writable. 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 ).

Mount the filesystem read-only.

Mount the filesystem read-write.

All I/O to the filesystem 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.

Allow an ordinary user to mount the filesystem. The name of the mounting user is written to mtab so that he can unmount the filesystem again. This option implies the options noexec, nosuid, and nodev (unless overridden by subsequent options, as in the option line user,exec,dev,suid).

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

Allow every user to mount and unmount the filesystem. This option implies the options noexec, nosuid, and nodev (unless overridden by subsequent options, as in the option line users,exec,dev,suid).

All options prefixed with "x-" are interpreted as comments or userspace applications specific options. These options are not stored to mtab file, send to mount.<type> helpers or mount(2) system call. The suggested format is x-<appname>.<option> (e.g. x-systemd.automount).

Allow to make a target directory (mountpoint). The optional argument <mode> specifies the file system access mode used for mkdir (2) in octal notation. The default mode is 0755. This functionality is supported only for root users.

Set the owner and group of the files in the filesystem (default: uid=gid=0).

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.

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

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 filesystem.

Set uid and gid of the root of the filesystem 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.

These options are accepted but ignored. (However, quota utilities may react to such strings in /etc/fstab.)

Set the owner and group of the mountpoint.

Sets the mode of the mountpoint.

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.

Support POSIX Access Control Lists (or not).

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 filesystem, while the bsddf behaviour (which is the default) is to subtract the overhead blocks used by the ext2 filesystem 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.)

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. The non-default behavior is unsupported (check=normal and check=strict options have been removed). Note that these mount options don't have to be supported if ext4 kernel driver is used for ext2 and ext3 filesystems.

Print debugging info upon each (re)mount.

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

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.

The usrquota (same as quota) mount option enables user quota support on the filesystem. grpquota enables group quotas support. You need the quota utilities to actually enable and manage the quota system.

Disables 32-bit UIDs and GIDs. This is for interoperability with older kernels which only store and expect 16-bit values.

Use old allocator or Orlov allocator for new inodes. Orlov is default.

The ext2 filesystem 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.)

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".

Support "user." extended attributes (or not).

Update the ext3 filesystem'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 filesystem's journal file; ext3 will create a new journal, overwriting the old contents of the file whose inode number is inum.

When the external journal device's major/minor numbers have changed, this option allows the user to specify the new journal location. The journal device is identified through its new major/minor numbers encoded in devnum.

Don't load the journal on mounting. Note that if the filesystem was not unmounted cleanly, skipping the journal replay will lead to the filesystem containing inconsistencies that can lead to any number of problems.

Specifies the journaling mode for file data. Metadata is always journaled. To use modes other than ordered on the root filesystem, pass the mode to the kernel as boot parameter, e.g. rootflags=data=journal.

This enables/disables barriers. barrier=0 disables it, barrier=1 enables it. Write barriers enforce proper on-disk ordering of journal commits, making volatile disk write caches safe to use, at some performance penalty. The ext3 filesystem does not enable write barriers by default. Be sure to enable barriers unless your disks are battery-backed one way or another. Otherwise you risk filesystem corruption in case of power failure.

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.

Enable POSIX Access Control Lists. See the acl(5) manual page.

Apart from the old quota system (as in ext2, jqfmt=vfsold aka version 1 quota) ext3 also supports journaled quotas (version 2 quota). jqfmt=vfsv0 enables journaled quotas. For journaled quotas the mount options usrjquota=aquota.user and grpjquota=aquota.group are required to tell the quota system which quota database files to use. Journaled quotas have the advantage that even after a crash no quota check is required.

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 'journal_checksum' internally.

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.

The ext4 filesystem enables write barriers by default.

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 value must be a power of 2. 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 filesystem blocks.

Deferring block allocation until write-out time.

Disable delayed allocation. Blocks are allocated 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 transaction 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 priority) 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.

Simulate the effects of calling ext4_abort() for debugging purposes. This is normally used while remounting a filesystem which is already mounted.

Many broken applications don't use fsync() when replacing existing files via patterns such as

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

Controls whether ext4 should issue discard/TRIM commands to the underlying block device when blocks are freed. This is useful for SSD devices and sparse/thinly-provisioned LUNs, but it is off by default until sufficient testing has been done.

Disables 32-bit UIDs and GIDs. This is for interoperability with older kernels which only store and expect 16-bit values.

Allows to resize filesystem to the end of the last existing block group, further resize has to be done with resize2fs either online, or offline. It can be used only with conjunction with remount.

This options allows to enables/disables the in-kernel facility for tracking filesystem metadata blocks within internal data structures. This allows multi- block allocator and other routines to quickly locate extents which might overlap with filesystem metadata blocks. This option is intended for debugging purposes and since it negatively affects the performance, it is off by default.

Controls whether or not ext4 should use the DIO read locking. If the dioread_nolock option is specified ext4 will allocate uninitialized extent before buffer write and convert the extent to initialized after IO completes. This approach allows ext4 code to avoid using inode mutex, which improves scalability on high speed storages. However this does not work with data journaling and dioread_nolock option will be ignored with kernel warning. Note that dioread_nolock code path is only used for extent-based files. Because of the restrictions this options comprises it is off by default (e.g. dioread_lock).

Enable 64-bit inode version support. This option is off by default.

Set blocksize (default 512). This option is obsolete.

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.

Three different levels of pickyness can be chosen:

Sets the codepage for converting to shortname characters on FAT and VFAT filesystems. By default, codepage 437 is used.

The fat filesystem can perform CRLF<-->NL (MS-DOS text format to UNIX text format) conversion in the kernel. The following conversion modes are available:

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.

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

If set, causes discard/TRIM commands to be issued to the block device when blocks are freed. This is useful for SSD devices and sparse/thinly-provisioned LUNs.

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.

If set, enables in-memory indexing of directory inodes to reduce the frequency of ESTALE errors in NFS client operations. Useful only when the filesystem is exported via NFS.

This option disables the conversion of timestamps between local time (as used by Windows on FAT) and UTC (which Linux uses internally). This is particularly useful when mounting devices (like digital cameras) that are set to UTC in order to avoid the pitfalls of local time.

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.

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.

Various misguided attempts to force Unix or DOS conventions onto a FAT filesystem.

Set the creator/type values as shown by the MacOS finder used for creating new files. Default values: '????'.

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

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.

Don't complain about invalid mount options.

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.

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

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.

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

Disable the use of Microsoft Joliet extensions, even if available. Cf. map.

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.)

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

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.)

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.)

(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.)

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.)

Character set to use for converting 16 bit Unicode characters on CD to 8 bit characters. The default is iso8859-1.

Convert 16 bit Unicode characters on CD to UTF-8.

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 ends.

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.

Define the behaviour when an error is encountered. (Either ignore errors and just mark the filesystem erroneous and continue, or remount the filesystem read-only, or panic and halt the system.)

These options are accepted but ignored.

Character set to use when returning file names. Unlike VFAT, NTFS suppresses names that contain nonconvertible characters. Deprecated.

New name for the option earlier called iocharset.

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 filesystem distinguishes between upper and lower case. The 8.3 alias names are presented as hard links instead of being suppressed. This option is obsolete.

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.

These options are recognized, but have no effect as far as I can see.

Instructs version 3.6 reiserfs software to mount a version 3.5 filesystem, using the 3.6 format for newly created objects. This filesystem will no longer be compatible with reiserfs 3.5 tools.

Choose which hash function reiserfs will use to find files within directories.

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.

Disable journaling. 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 journaling operations, save for actual writes into its journaling area. Implementation of nolog is a work in progress.

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 filesystem. 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 ftp://ftp.namesys.com/pub/reiserfsprogs.

Enable Extended User Attributes. See the attr(5) manual page.

Enable POSIX Access Control Lists. See the acl(5) manual page.

This enables/disables the use of write barriers in the journaling code. barrier=none disables it, barrier=flush enables it. Write barriers enforce proper on-disk ordering of journal commits, making volatile disk write caches safe to use, at some performance penalty. The reiserfs filesystem does not enable write barriers by default. Be sure to enable barriers unless your disks are battery-backed one way or another. Otherwise you risk filesystem corruption in case of power failure.

Override default maximum size of the filesystem. The size is given in bytes, and rounded up 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.

Set initial permissions of the root directory.

The user id.

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 ...'

Alternative ! separator may be used instead of :.

Enable bulk-read. VFS read-ahead is disabled because it slows down the file system. Bulk-Read is an internal optimization. Some flashes may read faster if the data are read at one go, rather than at several read requests. For example, OneNAND can do "read-while-load" if it reads more than one NAND page.

Do not bulk-read. This is the default.

Check data CRC-32 checksums. This is the default.

Do not check data CRC-32 checksums. With this option, the filesystem does not check CRC-32 checksum for data, but it does check it for the internal indexing information. This option only affects reading, not writing. CRC-32 is always calculated when writing the data.

Select the default compressor which is used when new files are written. It is still possible to read compressed files if mounted with the none option.

Set the default group.

Set the default umask. The value is given in octal.

Set the default user.

Show otherwise hidden files.

Show deleted files in lists.

Unset strict conformance.

Set the NLS character set.

Set the block size. (May not work unless 2048.)

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)

UFS is a filesystem 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:

Set behaviour on error:

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).

Allow two files with names that only differ in case. This option is obsolete.

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

UTF8 is the filesystem safe 8-bit encoding of Unicode that is used by the console. It can 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: :

Set the owner and group and mode of the device files in the usbfs filesystem (default: uid=gid=0, mode=0644). The mode is given in octal.

Set the owner and group and mode of the bus directories in the usbfs filesystem (default: uid=gid=0, mode=0555). The mode is given in octal.

Set the owner and group and mode of the file devices (default: uid=gid=0, mode=0444). The mode is given in octal.

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.

The default behaviour is for dynamic end-of-file preallocation size, which uses a set of heuristics to optimise the preallocation size based on the current allocation patterns within the file and the access patterns to the file. Specifying a fixed allocsize value turns off the dynamic behaviour.

The options enable/disable 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 when attr2 is selected (either when setting or removing extended attributes) the on-disk superblock feature bit field will be updated to reflect this format being in use.

The default behaviour is determined by the on-disk feature bit indicating that attr2 behaviour is active. If either mount option it set, then that becomes the new default used by the filesystem.

CRC enabled filesystems always use the attr2 format, and so will reject the noattr2 mount option if it is set.

Enables/disables the use of block layer write barriers for writes into the journal and for data integrity operations. This allows for drive level write caching to be enabled, for devices that support write barriers.

Enable/disable the issuing of commands to let the block device reclaim space freed by the filesystem. This is useful for SSD devices, thinly provisioned LUNs and virtual machine images, but may have a performance impact.

	Note
	It is currently recommended that you use the fstrim application to discard unused blocks rather than the discard mount option because the performance impact of this option is quite severe.

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 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.

Make the data allocator use the filestreams allocation mode across the entire filesystem rather than just on directories configured to use it.

When ikeep is specified, XFS does not delete empty inode clusters and keeps them around on disk. When noikeep is specified, empty inode clusters are returned to the free space pool.

When inode32 is specified, it indicates that XFS limits inode creation to locations which will not result in inode numbers with more than 32 bits of significance.

When inode64 is specified, it 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.

inode32 is provided for backwards compatibility with older systems and applications, since 64 bits inode numbers might cause problems for some applications that cannot handle large inode numbers. If applications are in use which do not handle inode numbers bigger than 32 bits, the inode32 option should be specified.

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. This is typically the page size of the machine, as this is the granularity of the page cache.

If "largeio" specified, a filesystem that was created with 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. Otherwise the behaviour is the same 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.

If the memory cost of 8 log buffers is too high on small systems, then it may be reduced at some cost to performance on metadata intensive workloads. The logbsize option below controls the size of each buffer and so is also relevent to this case.

Set the size of each in-memory log buffer. The 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 logbsize must be an integer multiple of the log stripe unit configured at mkfs time.

The default value for version 1 logs is 32768, while the default value for version 2 logs is MAX(32768, log_sunit).

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.

Data allocations will not be aligned at stripe unit boundaries. This is only relevant to filesystems created with non-zero data alignment parameters (sunit, swidth) by mkfs.

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.

Don't check for double mounted file systems using the file system uuid. This is useful to mount LVM snapshot volumes, and often used in combination with "norecovery" for mounting read-only snapshots.

Forcibly turns off all quota accounting and enforcement within the filesystem.

User disk quota accounting enabled, and limits (optionally) enforced. Refer to xfs_quota(8) for further details.

Group disk quota accounting enabled and limits (optionally) enforced. Refer to xfs_quota(8) for further details.

Project disk quota accounting enabled and limits (optionally) enforced. Refer to xfs_quota(8) for further details.

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. These options are only relevant to filesystems that were created with non-zero data alignment parameters.

The sunit and swidth parameters specified must be compatible with the existing filesystem alignment characteristics. In general, that means the only valid changes to sunit are increasing it by a power-of-2 multiple. Valid swidth values are any integer multiple of a valid sunit value.

Typically the only time these mount options are necessary if after an underlying RAID device has had it's geometry modified, such as adding a new disk to a RAID5 lun and reshaping it.

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.

When specified, all filesystem namespace operations are executed synchronously. This ensures that when the namespace operation (create, unlink, etc) completes, the change to the namespace is on stable storage. This is useful in HA setups where failover must not result in clients seeing inconsistent namespace presentation during or after a failover event.

success

incorrect invocation or permissions

system error (out of memory, cannot fork, no more loop devices)

internal mount bug

user interrupt

problems writing or locking /etc/mtab

mount failure

some mount succeeded

The command mount -a returns 0 (all success), 32 (all failed) or 64 (some failed, some success).

filesystem table

table of mounted filesystems

lock file

temporary file

a list of filesystem types to try

overrides the default location of the fstab file

overrides the default location of the mtab file

enables debug output