neulab/tldr huggingface dataset:
The mount program does not read the /etc/fstab file if both device (or LABEL, UUID, ID, PARTUUID or PARTLABEL) and dir are specified. For example, to mount device foo at /dir:
mount /dev/foo /dir
This default behaviour can be changed by using the --options-source-force command-line option to always read configuration from fstab. For non-root users mount always reads the fstab configuration.
Non-superuser mounts Normally, only the superuser can mount filesystems. However, when fstab contains the user option on a line, anybody can mount the corresponding filesystem.
Thus, given a line
/dev/cdrom /cd iso9660 ro,user,noauto,unhide
any user can mount the iso9660 filesystem found on an inserted CDROM using the command:
mount /cd
Note that mount is very strict about non-root users and all paths specified on command line are verified before fstab is parsed or a helper program is executed. It’s strongly recommended to use a valid mountpoint to specify filesystem, otherwise mount may fail. For example it’s a bad idea to use NFS or CIFS source on command line.
Since util-linux 2.35, mount does not exit when user permissions are inadequate according to libmount’s internal security rules. Instead, it drops suid permissions and continues as regular non-root user. This behavior supports use-cases where root permissions are not necessary (e.g., fuse filesystems, user namespaces, etc).
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 it, 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 a member of the group of the special file.
Bind mount operation Remount part of the file hierarchy somewhere else. The call is:
mount --bind olddir newdir
or by using this fstab entry:
/olddir /newdir none bind
After this call the same contents are accessible in two places.
It is important to understand that "bind" does not create any second-class or special node in the kernel VFS. The "bind" is just another operation to attach a filesystem. There is nowhere stored information that the filesystem has been attached by a "bind" operation. The olddir and newdir are independent and the olddir may be unmounted.
One can also remount a single file (on a single file). It’s also possible to use a bind mount to create a mountpoint from a regular directory, for example:
mount --bind foo foo
The bind mount call attaches only (part of) a single filesystem, not possible submounts. The entire file hierarchy including submounts can be attached a second place by using:
mount --rbind olddir newdir
Note that the filesystem mount options maintained by the kernel will remain the same as those on the original mount point. The userspace mount options (e.g., _netdev) will not be copied by mount and it’s necessary to explicitly specify the options on the mount command line.
Since util-linux 2.27 mount permits changing the mount options by passing the relevant options along with --bind. For example:
mount -o bind,ro foo foo
This feature is not supported by the Linux kernel; it is implemented in userspace by an additional mount(2) remounting system call. This solution is not atomic.
The alternative (classic) way to create a read-only bind mount is to use the remount operation, for example:
mount --bind olddir newdir mount -o remount,bind,ro olddir newdir
Note that a read-only bind will create a read-only mountpoint (VFS entry), but the original filesystem superblock will still be writable, meaning that the olddir will be writable, but the newdir will be read-only.
It’s also possible to change nosuid, nodev, noexec, noatime, nodiratime and relatime VFS entry flags via a "remount,bind" operation. The other flags (for example filesystem-specific flags) are silently ignored. It’s impossible to change mount options recursively (for example with -o rbind,ro).
Since util-linux 2.31, mount ignores the bind flag from /etc/fstab on a remount operation (if "-o remount" is specified on command line). This is necessary to fully control mount options on remount by command line. In previous versions the bind flag has been always applied and it was impossible to re-define mount options without interaction with the bind semantic. This mount behavior does not affect situations when "remount,bind" is specified in the /etc/fstab file.
The move operation Move a mounted tree to another place (atomically). The call is:
mount --move olddir newdir
This will cause the contents which previously appeared under olddir to now be accessible under newdir. The physical location of the files is not changed. Note that olddir has to be a mountpoint.
Note also that moving a mount residing under a shared mount is invalid and unsupported. Use findmnt -o TARGET,PROPAGATION to see the current propagation flags.
Shared subtree 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 the ability to create mirrors of that mount such that mounts and unmounts within any of the mirrors propagate to the other mirror. A slave mount receives propagation from its master, but not vice versa. A private mount carries no propagation abilities. An unbindable mount is a private mount which cannot be cloned through a bind operation. The detailed semantics are documented in Documentation/filesystems/sharedsubtree.txt file in the kernel source tree; see also mount_namespaces(7).
Supported operations are:
mount --make-shared mountpoint mount --make-slave mountpoint mount --make-private mountpoint mount --make-unbindable mountpoint
The following commands allow 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
mount(8) does not read fstab(5) when a --make-* operation is requested. All necessary information has to be specified on the command line.
Note that the Linux kernel does not allow changing multiple propagation flags with a single mount(2) system call, and the flags cannot be mixed with other mount options and operations.
Since util-linux 2.23 the mount command can be used to do more propagation (topology) changes by one mount(8) call and do it also together with other mount operations. The propagation flags are applied by additional mount(2) system calls when the preceding mount operations were successful. Note that this use case is not atomic. It is possible to specify the propagation flags in fstab(5) as mount options (private, slave, shared, unbindable, rprivate, rslave, rshared, runbindable).
mount --make-private --make-unbindable /dev/sda1 /foo
is the same as:
mount /dev/sda1 /foo mount --make-private /foo mount --make-unbindable /foo
COMMAND-LINE OPTIONS The full set of mount options used by an invocation of mount is determined by first extracting the mount options for the filesystem from the fstab table, then applying any options specified by the -o argument, and finally applying a -r or -w option, when present.
The mount command does not pass all command-line options to the /sbin/mount.suffix mount helpers. The interface between mount and the mount helpers is described below in the section EXTERNAL HELPERS.
Command-line options available for the mount command are:
-a, --all Mount all filesystems (of the given types) mentioned in fstab (except for those whose line contains the noauto keyword). The filesystems are mounted following their order in fstab. The mount command compares filesystem source, target (and fs root for bind mount or btrfs) to detect already mounted filesystems. The kernel table with already mounted filesystems is cached during mount --all. This means that all duplicated fstab entries will be mounted.
The option --all is possible to use for remount operation too. In this case all filters (-t and -O) are applied to the table of already mounted filesystems.
Since version 2.35 is possible to use the command line option -o to alter mount options from fstab (see also --options-mode).
Note that it is a bad practice to use mount -a for fstab checking. The recommended solution is findmnt --verify.
-B, --bind Remount a subtree somewhere else (so that its contents are available in both places). See above, under Bind mounts.
-c, --no-canonicalize Don’t canonicalize paths. The mount command canonicalizes all paths (from the command line or fstab) by default. This option can be used together with the -f flag for already canonicalized absolute paths. The option is designed for mount helpers which call mount -i. It is strongly recommended to not use this command-line option for normal mount operations.
Note that mount does not pass this option to the /sbin/mount.type helpers.
-F, --fork (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 proceed in parallel. A disadvantage is that the order of the mount operations is undefined. Thus, you cannot use this option if you want to mount both /usr and /usr/spool.
-f, --fake 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 an existing record in /etc/mtab and fails when the record already exists (with a regular non-fake mount, this check is done by the kernel).
-i, --internal-only Don’t call the /sbin/mount.filesystem helper even if it exists.
-L, --label label Mount the partition that has the specified label.
-l, --show-labels Add the labels in the mount output. mount must have permission to read the disk device (e.g. be set-user-ID 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).
-M, --move Move a subtree to some other place. See above, the subsection The move operation.
-n, --no-mtab Mount without writing in /etc/mtab. This is necessary for example when /etc is on a read-only filesystem.
-N, --namespace ns Perform the mount operation in the mount namespace specified by ns. ns is either PID of process running in that namespace or special file representing that namespace.
mount switches to the mount namespace when it reads /etc/fstab, writes /etc/mtab: (or writes to _/run/mount) and calls the mount(2) system call, otherwise it runs in the original mount namespace. This means that the target namespace does not have to contain any libraries or other requirements necessary to execute the mount(2) call.
-O, --test-opts opts Limit the set of filesystems to which the -a option applies. In this regard it is like the -t option except that -O is useless without -a. For example, the command
mount -a -O no_netdev
mounts all filesystems 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 opts Use the specified mount options. The opts argument is a comma-separated list. For example:
mount LABEL=mydisk -o noatime,nodev,nosuid
For more details, see the FILESYSTEM-INDEPENDENT MOUNT OPTIONS and FILESYSTEM-SPECIFIC MOUNT OPTIONS sections.
--options-mode mode Controls how to combine options from fstab/mtab with options from the command line. mode can be one of ignore, append, prepend or replace. For example, append means that options from fstab are appended to options from the command line. The default value is prepend — it means command line options are evaluated after fstab options. Note that the last option wins if there are conflicting ones.
--options-source source Source of default options. source is a comma-separated list of fstab, mtab and disable. disable disables fstab and mtab and disables --options-source-force. The default value is fstab,mtab.
--options-source-force Use options from fstab/mtab even if both device and dir are specified.
-R, --rbind Remount a subtree and all possible submounts somewhere else (so that its contents are available in both places). See above, the subsection Bind mounts.
-r, --read-only Mount the filesystem read-only. A synonym is -o ro.
Note that, depending on the filesystem type, state and kernel behavior, the system may still write to the device. For example, ext3 and ext4 will replay the journal if the filesystem is dirty. To prevent this kind of write access, you may want to mount an ext3 or ext4 filesystem with the ro,noload mount options or set the block device itself to read-only mode, see the blockdev(8) command.
-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. Currently it’s supported by the mount.nfs mount helper only.
--source device If only one argument for the mount command is given, then the argument might be interpreted as the target (mountpoint) or source (device). This option allows you to explicitly define that the argument is the mount source.
--target directory If only one argument for the mount command is given, then the argument might be interpreted as the target (mountpoint) or source (device). This option allows you to explicitly define that the argument is the mount target.
--target-prefix directory Prepend the specified directory to all mount targets. This option can be used to follow fstab, but mount operations are done in another place, for example:
mount --all --target-prefix /chroot -o X-mount.mkdir
mounts all from system fstab to /chroot, all missing mountpoint are created (due to X-mount.mkdir). See also --fstab to use an alternative fstab.
-T, --fstab path Specifies an alternative fstab file. If path is a directory, then the files in the directory are sorted by strverscmp(3); files that start with "." or without an .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 beyond standard system configuration.
Note that mount does not pass the option --fstab to the /sbin/mount.type helpers, meaning 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 the user’s rights.
-t, --types fstype The argument following the -t is used to indicate the filesystem type. The filesystem types which are currently supported depend on the running kernel. See /proc/filesystems and /lib/modules/$(uname -r)/kernel/fs for a complete list of the filesystems. The most common are ext2, ext3, ext4, xfs, btrfs, vfat, sysfs, proc, nfs and cifs.
The programs mount and umount(8) support filesystem subtypes. The subtype is defined by a '.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).
If no -t option is given, or if the auto type is specified, mount will try to guess the desired type. mount uses the libblkid(3) 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 *, mount will read /proc/filesystems afterwards. While trying, all filesystem types will be mounted with the 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, for the -t option as well as in an /etc/fstab entry. The list of filesystem types for the -t option can be prefixed with no to specify the filesystem types on which no action should be taken. The prefix no has no effect when specified in an /etc/fstab entry.
The prefix no can be meaningful with the -a option. For example, the command
mount -a -t nomsdos,smbfs
mounts all filesystems except those of type msdos and smbfs.
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) an 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 different 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.
-U, --uuid uuid Mount the partition that has the specified uuid.
-w, --rw, --read-write Mount the filesystem read/write. Read-write is the kernel default and the mount default is to try read-only if the previous mount syscall with read-write flags on write-protected devices of filesystems failed.
A synonym is -o rw.
Note that specifying -w on the command line forces mount to never try read-only mount on write-protected devices or already mounted read-only filesystems.
FILESYSTEM-INDEPENDENT MOUNT OPTIONS 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. Note that filesystems also have per-filesystem specific default mount options (see for example tune2fs -l output for ext_N_ filesystems).
The following options apply to any filesystem that is being mounted (but not every filesystem actually honors them - e.g., the sync option today has an effect only for ext2, ext3, ext4, fat, vfat, ufs and xfs):
async All I/O to the filesystem should be done asynchronously. (See also the sync option.)
atime Do not use the noatime feature, so the inode access time is controlled by kernel defaults. See also the descriptions of the relatime and strictatime mount options.
noatime Do not update inode access times on this filesystem (e.g. for faster access on the news spool to speed up news servers). This works for all inode types (directories too), so it implies nodiratime.
auto Can be mounted with the -a option.
noauto Can only be mounted explicitly (i.e., the -a option will not cause the filesystem 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 or ext4 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.
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 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:
mount -t tmpfs none /mnt -o \ 'context="system_u:object_r:tmp_t:s0:c127,c456",noexec'
For more details, see selinux(8).
defaults Use the default options: rw, suid, dev, exec, auto, nouser, and async.
Note that the real set of all default mount options depends on the kernel and filesystem type. See the beginning of this section for more details.
dev Interpret character or block special devices on the filesystem.
nodev Do not interpret character or block special devices on the filesystem.
diratime Update directory inode access times on this filesystem. This is the default. (This option is ignored when noatime is set.)
nodiratime Do not update directory inode access times on this filesystem. (This option is implied when noatime is set.)
dirsync All directory updates within the filesystem should be done synchronously. This affects the following system calls: creat(2), link(2), unlink(2), symlink(2), mkdir(2), rmdir(2), mknod(2) and rename(2).
exec Permit execution of binaries.
noexec Do not permit direct execution of any binaries on the mounted filesystem.
group Allow an ordinary user to mount the filesystem if one of that user’s 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).
iversion Every time the inode is modified, the i_version field will be incremented.
noiversion Do not increment the i_version inode field.
mand Allow mandatory locks on this filesystem. See fcntl(2).
nomand Do not allow mandatory locks on this filesystem.
_netdev 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.
relatime 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 it doesn’t break mutt(1) 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.
norelatime Do not use the relatime feature. See also the strictatime mount option.
strictatime Allows to explicitly request full atime updates. This makes it possible for the kernel to default to relatime or noatime but still allow userspace to override it. For more details about the default system mount options see /proc/mounts.
nostrictatime Use the kernel’s default behavior for inode access time updates.
lazytime Only update times (atime, mtime, ctime) on the in-memory version of the file inode.
This mount option significantly reduces writes to the inode table for workloads that perform frequent random writes to preallocated files.
The on-disk timestamps are updated only when:
•   the inode needs to be updated for some change unrelated to file timestamps
•   the application employs fsync(2), syncfs(2), or sync(2)
•   an undeleted inode is evicted from memory
•   more than 24 hours have passed since the inode was written to disk.
nolazytime Do not use the lazytime feature.
suid Honor set-user-ID and set-group-ID bits or file capabilities when executing programs from this filesystem.
nosuid Do not honor set-user-ID and set-group-ID bits or file capabilities when executing programs from this filesystem. In addition, SELinux domain transitions require permission nosuid_transition, which in turn needs also policy capability nnp_nosuid_transition.
silent Turn on the silent flag.
loud Turn off the silent flag.
owner Allow an ordinary user to mount the filesystem if that user 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).
remount 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 operation together with the bind flag has special semantics. See above, the subsection Bind mounts.
The remount functionality follows the standard way the mount command works with options from fstab. This means that mount does not read fstab (or mtab) only when both device and dir are specified.
mount -o remount,rw /dev/foo /dir
After this call all old mount options are replaced and arbitrary stuff from fstab (or mtab) 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 and merges these options with the options from the command line (-o). If no mountpoint is found in fstab, then a remount with unspecified source is allowed.
mount allows the use of --all to remount all already mounted filesystems which match a specified filter (-O and -t). For example:
mount --all -o remount,ro -t vfat
remounts all already mounted vfat filesystems in read-only mode. Each of the filesystems is remounted by mount -o remount,ro /dir semantic. This means the mount command reads fstab or mtab and merges these options with the options from the command line.
ro Mount the filesystem read-only.
rw Mount the filesystem read-write.
sync All I/O to the filesystem should be done synchronously. In the case of media with a limited number of write cycles (e.g. some flash drives), sync may cause life-cycle shortening.
user Allow an ordinary user to mount the filesystem. The name of the mounting user is written to the mtab file (or to the private libmount file in /run/mount on systems without a regular mtab) so that this same user 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).
nouser Forbid an ordinary user to mount the filesystem. This is the default; it does not imply any other options.
users Allow any user to mount and to unmount the filesystem, even when some other ordinary user mounted it. This option implies the options noexec, nosuid, and nodev (unless overridden by subsequent options, as in the option line users,exec,dev,suid).
X-* All options prefixed with "X-" are interpreted as comments or as userspace application-specific options. These options are not stored in user space (e.g., mtab file), nor sent to the mount.type helpers nor to the mount(2) system call. The suggested format is X-appname.option.
x-* The same as X-* options, but stored permanently in user space. This means the options are also available for umount(8) or other operations. Note that maintaining mount options in user space is tricky, because it’s necessary use libmount-based tools and there is no guarantee that the options will be always available (for example after a move mount operation or in unshared namespace).
Note that before util-linux v2.30 the x-* options have not been maintained by libmount and stored in user space (functionality was the same as for X-* now), but due to the growing number of use-cases (in initrd, systemd etc.) the functionality has been extended to keep existing fstab configurations usable without a change.
X-mount.mkdir[=mode] Allow to make a target directory (mountpoint) if it does not exit yet. The optional argument mode specifies the filesystem access mode used for mkdir(2) in octal notation. The default mode is 0755. This functionality is supported only for root users or when mount executed without suid permissions. The option is also supported as x-mount.mkdir, this notation is deprecated since v2.30.
nosymfollow Do not follow symlinks when resolving paths. Symlinks can still be created, and readlink(1), readlink(2), realpath(1), and realpath(3) all still work properly.
FILESYSTEM-SPECIFIC MOUNT OPTIONS This section lists options that are specific to particular filesystems. Where possible, you should first consult filesystem-specific manual pages for details. Some of those pages are listed in the following table.
┌─────────────────┬───────────────┐ │                 │               │ │Filesystem(s)    │ Manual page   │ ├─────────────────┼───────────────┤ │                 │               │ │btrfs            │ btrfs(5)      │ ├─────────────────┼───────────────┤ │                 │               │ │cifs             │ mount.cifs(8) │ ├─────────────────┼───────────────┤ │                 │               │ │ext2, ext3, ext4 │ ext4(5)       │ ├─────────────────┼───────────────┤ │                 │               │ │fuse             │ fuse(8)       │ ├─────────────────┼───────────────┤ │                 │               │ │nfs              │ nfs(5)        │ ├─────────────────┼───────────────┤ │                 │               │ │tmpfs            │ tmpfs(5)      │ ├─────────────────┼───────────────┤ │                 │               │ │xfs              │ xfs(5)        │ └─────────────────┴───────────────┘
Note that some of the pages listed above might be available only after you install the respective userland tools.
The following options apply only to certain filesystems. We sort them by filesystem. All options follow the -o flag.
What options are supported depends a bit on the running kernel. Further information may be available in filesystem-specific files 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 filesystem (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.rst.
Mount options for affs uid=value and gid=value 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).
setuid=value and setgid=value Set the owner and group of all files.
mode=value Set the mode of all files to value & 0777 disregarding the original permissions. Add search permission to directories that have read permission. The value is given in octal.
protect Do not allow any changes to the protection bits on the filesystem.
usemp 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...
verbose Print an informational message for each successful mount.
prefix=string Prefix used before volume name, when following a link.
volume=string Prefix (of length at most 30) used before '/' when following a symbolic link.
reserved=value (Default: 2.) Number of unused blocks at the start of the device.
root=value Give explicitly the location of the root block.
bs=value Give blocksize. Allowed values are 512, 1024, 2048, 4096.
grpquota|noquota|quota|usrquota These options are accepted but ignored. (However, quota utilities may react to such strings in /etc/fstab.)
Mount options for debugfs The debugfs filesystem is a pseudo filesystem, traditionally mounted on /sys/kernel/debug. As of kernel version 3.4, debugfs has the following options:
uid=n, gid=n Set the owner and group of the mountpoint.
mode=value Sets the mode of the mountpoint.
Mount options for devpts The devpts filesystem is a pseudo filesystem, 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 pseudo terminals 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 pseudo terminals to belong to the tty group.
mode=value Set the mode of newly created pseudo terminals to the specified value. The default is 0600. A value of mode=620 and gid=5 makes "mesg y" the default on newly created pseudo terminals.
newinstance Create a private instance of the devpts filesystem, such that indices of pseudo terminals 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 pseudo terminal indices (i.e., legacy mode). Each mount of devpts with the newinstance option has a private set of pseudo terminal 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.
ptmxmode=value 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 fat (Note: fat is not a separate filesystem, but a common part of the msdos, umsdos and vfat filesystems.)
blocksize={512|1024|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.)
umask=value Set the umask (the bitmask of the permissions that are not present). The default is the umask of the current process. The value is given in octal.
dmask=value Set the umask applied to directories only. The default is the umask of the current process. The value is given in octal.
fmask=value Set the umask applied to regular files only. The default is the umask of the current process. The value is given in octal.
allow_utime=value 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 that the current process is owner of the file, or that it has the CAP_FOWNER capability. But FAT filesystems don’t have UID/GID on disk, so the normal check is too inflexible. With this option you can relax it.
check=value Three different levels of pickiness can be chosen:
r[elaxed] Upper and lower case are accepted and equivalent, long name parts are truncated (e.g. verylongname.foobar becomes verylong.foo), leading and embedded spaces are accepted in each name part (name and extension).
n[ormal] Like "relaxed", but many special characters (*, ?, <, spaces, etc.) are rejected. This is the default.
s[trict] Like "normal", but names that contain long parts or special characters that are sometimes used on Linux but are not accepted by MS-DOS (+, =, etc.) are rejected.
codepage=value Sets the codepage for converting to shortname characters on FAT and VFAT filesystems. By default, codepage 437 is used.
conv=mode This option is obsolete and may fail or be ignored.
cvf_format=module 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.
cvf_option=option Option passed to the CVF module. This option is obsolete.
debug 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).
discard 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.
dos1xfloppy If set, use a fallback default BIOS Parameter Block configuration, determined by backing device size. These static parameters match defaults assumed by DOS 1.x for 160 kiB, 180 kiB, 320 kiB, and 360 kiB floppies and floppy images.
errors={panic|continue|remount-ro} Specify FAT behavior on critical errors: panic, continue without doing anything, or remount the partition in read-only mode (default behavior).
fat={12|16|32} Specify a 12, 16 or 32 bit fat. This overrides the automatic FAT type detection routine. Use with caution!
iocharset=value 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.
nfs={stale_rw|nostale_ro} Enable this only if you want to export the FAT filesystem over NFS.
stale_rw: This option maintains an index (cache) of directory inodes which is used by the nfs-related code to improve look-ups. Full file operations (read/write) over NFS are supported but with cache eviction at NFS server, this could result in spurious ESTALE errors.
nostale_ro: This option bases the inode number and file handle on the on-disk location of a file in the FAT directory entry. This ensures that ESTALE will not be returned after a file is evicted from the inode cache. However, it means that operations such as rename, create and unlink could cause file handles that previously pointed at one file to point at a different file, potentially causing data corruption. For this reason, this option also mounts the filesystem readonly.
To maintain backward compatibility, -o nfs is also accepted, defaulting to stale_rw.
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 particularly useful when mounting devices (like digital cameras) that are set to UTC in order to avoid the pitfalls of local time.
time_offset=minutes Set offset for conversion of timestamps from local time used by FAT to UTC. I.e., minutes will be subtracted from each timestamp to convert it to UTC used internally by Linux. This is useful when the time zone set in the kernel via settimeofday(2) is not the time zone used by the filesystem. Note that this option still does not provide correct time stamps in all cases in presence of DST - time stamps in a different DST setting will be off by one hour.
quiet Turn on the quiet flag. Attempts to chown or chmod files do not return errors, although they fail. Use with caution!
rodir FAT has the ATTR_RO (read-only) attribute. On Windows, the ATTR_RO of the directory will just be ignored, and is used only by applications as a flag (e.g. it’s set for the customized folder).
If you want to use ATTR_RO as read-only flag even for the directory, set this option.
showexec 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.
sys_immutable 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.
usefree 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 filesystem.
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.
session=n 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.
part=n 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.)
case={lower|asis} Convert all files names to lower case, or leave them. (Default: case=lower.)
conv=mode This option is obsolete and may fail or being ignored.
nocheck 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 an 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 filesystem (except that it is read-only, of course).
norock Disable the use of Rock Ridge extensions, even if available. Cf. map.
nojoliet Disable the use of Microsoft Joliet extensions, even if available. Cf. map.
check={r[elaxed]|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 filesystem the indicated user or group id, possibly overriding the information found in the Rock Ridge extensions. (Default: uid=0,gid=0.)
map={n[ormal]|o[ff]|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.
mode=value For non-Rock Ridge volumes, give all files the indicated mode. (Default: read and execute permission for everybody.) Octal mode values require 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.)
block={512|1024|2048} Set the block size to the indicated value. (Default: block=1024.)
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 16 MB.
session=x Select number of session on a multisession CD.
sbsector=xxx Session begins from sector xxx.
The following options are the same as for vfat and specifying them only makes sense when using discs encoded using Microsoft’s Joliet extensions.
iocharset=value 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 iocharset=name 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=value 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.
nointegrity 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.
integrity 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|remount-ro|panic} Define the behavior 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.)
noquota|quota|usrquota|grpquota These options are accepted but ignored.
Mount options for msdos See mount options for fat. If the msdos filesystem detects an inconsistency, it reports an error and sets the file system read-only. The filesystem can be made writable 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 ntfs iocharset=name Character set to use when returning file names. Unlike VFAT, NTFS suppresses names that contain nonconvertible characters. Deprecated.
nls=name New name for the option earlier called iocharset.
utf8 Use UTF-8 for converting file names.
uni_xlate={0|1|2} 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 gives a little-endian encoding and 1 a byteswapped bigendian encoding.
posix=[0|1] 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.
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 overlay Since Linux 3.18 the overlay pseudo filesystem implements a union mount for other filesystems.
An overlay filesystem combines two filesystems - an upper filesystem and a lower filesystem. When a name exists in both filesystems, the object in the upper filesystem is visible while the object in the lower filesystem is either hidden or, in the case of directories, merged with the upper object.