MOUNT(8) System Administration MOUNT(8) NAME mount - mount a filesystem SYNOPSIS mount [-lhV] mount -a [-fFnrsvw] [-t vfstype] [-O optlist] mount [-fnrsvw] [-o option[,option]...] device|dir mount [-fnrsvw] [-t vfstype] [-o options] device dir DESCRIPTION All files accessible in a Unix system are arranged in one big tree, the file hierarchy, rooted at /. These files can be spread out over several devices. The mount command serves to attach the filesystem found on some device to the big file tree. Conversely, the umount(8) command will detach it again. The standard form of the mount command is: mount -t type device dir This tells the kernel to attach the filesystem found on device (which is of type type) at the directory dir. The previous contents (if any) and owner and mode of dir become invisible, and as long as this filesystem remains mounted, the pathname dir refers to the root of the filesystem on device. If only the directory or the device is given, for example: mount /dir then mount looks for a mountpoint (and if not found then for a device) in the /etc/fstab file. It's possible to use the --target or --source options to avoid ambivalent interpretation of the given argument. For example: mount --target /mountpoint The listing. The listing mode is maintained for backward compatibility only. For more robust and customizable output use findmnt(8), especially in your scripts. Note that control characters in the mountpoint name are replaced with '?'. The following command lists all mounted filesystems (of type type): mount [-l] [-t type] The option -l adds labels to this listing. See below. The device indication. Most devices are indicated by a filename (of a block special device), like /dev/sda1, but there are other possibilities. For example, in the case of an NFS mount, device may look like knuth.cwi.nl:/dir. It is also possible to indicate a block special device using its filesystem label or UUID (see the -L and -U options below), or its partition label or UUID. (Parti‐ tion identifiers are supported for example for GUID Partition Tables (GPT).) Don't forget that there is no guarantee that UUIDs and labels are really unique, especially if you move, share or copy the device. Use lsblk -o +UUID,PARTUUID to verify that the UUIDs are really unique in your system. The recommended setup is to use tags (e.g. LABEL=label) rather than /dev/disk/by-{label,uuid,partuuid,partlabel} udev symlinks in the /etc/fstab file. Tags are more readable, robust and portable. The mount(8) command internally uses udev symlinks, so the use of symlinks in /etc/fstab has no advantage over tags. For more details see libblkid(3). Note that mount(8) uses UUIDs as strings. The UUIDs from the command line or from fstab(5) are not converted to internal binary representation. The string representation of the UUID should be based on lower case characters. The proc filesystem is not associated with a special device, and when mounting it, an arbitrary keyword, such as proc can be used instead of a device specification. (The customary choice none is less fortunate: the error message `none busy' from umount can be confusing.) The /etc/fstab, /etc/mtab and /proc/mounts files. The file /etc/fstab (see fstab(5)), may contain lines describing what devices are usually mounted where, using which options. The default location of the fstab(5) file can be overridden with the --fstab path command-line option (see below for more details). The command mount -a [-t type] [-O optlist] (usually given in a bootscript) causes all filesystems mentioned in fstab (of the proper type and/or having or not having the proper options) to be mounted as indicated, except for those whose line contains the noauto keyword. Adding the -F option will make mount fork, so that the filesystems are mounted simultaneously. When mounting a filesystem mentioned in fstab or mtab, it suffices to specify on the command line only the device, or only the mount point. The programs mount and umount traditionally maintained list of currently mounted filesystems in the file /etc/mtab. The mtab file is still supported, but it's recommended to use a sym‐ link to the file /proc/mounts rather than the regular mtab file on the current Linux systems. The mtab file maintained in userspace cannot reliably work with namespaces, containers and another advanced Linux features. If no arguments are given to mount, this list is printed. If you want to override mount options from /etc/fstab you have to use the -o option: mount device|dir -o options and then the mount options from the command line will be appended to the list of options from /etc/fstab. The usual behavior is that the last option wins if there are conflicting ones. The mount program does not read the /etc/fstab file if both device (or LABEL, UUID, PARTUUID or PARTLABEL) and dir are specified. For example, to mount device foo at /dir: mount /dev/foo /dir The non-superuser mounts. Normally, only the superuser can mount filesystems. However, when fstab contains the user option on a line, anybody can mount the corresponding 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 /dev/cdrom or mount /cd For more details, see fstab(5). Only the user that mounted a filesystem can unmount it again. If any user should be able to unmount 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 member of the group of the special file. The bind mounts. Since Linux 2.4.0 it is possible to remount part of the file hierarchy somewhere else. The call is: mount --bind olddir newdir or by using this fstab entry: /olddir /newdir none bind After this call the same contents are accessible in two places. One can also remount a single file (on a single file). It's also possible to use the 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 is attached a second place by using: mount --rbind olddir newdir Note that the filesystem mount options will remain the same as those on the original mount point, and cannot be changed by passing the -o option along with --bind/--rbind. The mount options can be changed by a separate remount command, for example: mount --bind olddir newdir mount -o remount,ro newdir Note that the behavior of the remount operation depends on the /etc/mtab file. The first command stores the 'bind' flag in the /etc/mtab file and the second command reads the flag from the file. If you have a system without the /etc/mtab file or if you explicitly define source and target for the remount command (then mount(8) does not read /etc/mtab), then you have to use the bind flag (or option) for the remount command too. For example: mount --bind olddir newdir mount -o remount,ro,bind olddir newdir Note that remount,ro,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. The move operation. Since Linux 2.5.1 it is possible to atomically move a mounted tree to another place. The call is: mount --move olddir newdir 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. The 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 propaga‐ tion abilities. An unbindable mount is a private mount which cannot be cloned through a bind operation. The detailed semantics are documented in Documentation/filesystems/sharedsub‐ tree.txt file in the kernel source tree. 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 to change multiple propagation flags with a single mount(2) syscall, and the flags cannot be mixed with other mount options. Since util-linux 2.23 the mount command allows to use several propagation flags together and also together with other mount operations. This feature is EXPERIMENTAL. The propagation flags are applied by additional mount(2) syscalls when the preceeding 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). For example: 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 command mount 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: -V, --version Display version information and exit. -h, --help Display help text and exit. -v, --verbose Verbose mode. -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. -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 go in parallel. A disadvantage is that the mounts are done in undefined order. Thus, you cannot use this option if you want to mount both /usr and /usr/spool. -f, --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, --show-labels Add the labels in the mount output. mount must have permission to read the disk device (e.g. be suid root) for this to work. One can set such a label for ext2, ext3 or ext4 using the e2label(8) utility, or for XFS using xfs_admin(8), or for reiserfs using reiserfstune(8). -n, --no-mtab Mount without writing in /etc/mtab. This is necessary for example when /etc is on a read-only filesystem. -c, --no-canonicalize Don't canonicalize paths. The mount command canonicalizes all paths (from 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(8) does not pass this option to the /sbin/mount.type helpers. -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 dev 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 the mount source. --target dir 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 the mount target. -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. -w, --rw, --read-write Mount the filesystem read/write. This is the default. A synonym is -o rw. -L, --label label Mount the partition that has the specified label. -U, --uuid uuid Mount the partition that has the specified uuid. These two options require the file /proc/partitions (present since Linux 2.1.116) to exist. -T, --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(8) 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 vfstype The argument following the -t is used to indicate the filesystem type. The filesystem types which are currently supported include: adfs, affs, autofs, btrfs, 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 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). 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. 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 *, 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. 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 mount -a -t nomsdos,ext mounts all filesystems except those of type msdos and ext. -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. -B, --bind Remount a subtree somewhere else (so that its contents are available in both places). See above. -R, --rbind Remount a subtree and all possible submounts somewhere else (so that its contents are available in both places). See above. -M, --move Move a subtree to some other place. See above. 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 extN 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, fat, vfat and ufs): 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 strictatime and relatime 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). 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 run‐ ning 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 compati‐ bility with xattr-supporting filesystems on earlier 2.4. 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 supply‐ ing 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 sup‐ ports 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: 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 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 file system. diratime Update directory inode access times on this filesystem. This is the default. nodiratime Do not update directory inode access times on this filesystem. dirsync 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. exec Permit execution of binaries. noexec Do not permit 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.) group 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). 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 noa‐ time, but it 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. 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. suid Allow set-user-identifier or set-group-identifier bits to take effect. nosuid Do not allow set-user-identifier or set-group-identifier bits to take effect. silent Turn on the silent flag. loud Turn off the silent flag. owner 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). 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 functionality follows the standard way the mount command works with options from fstab. This means that the mount command only doesn't read fstab (or mtab) when both the 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 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 the options from the command line (-o). 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 mtab (or to the private libmount file in /run/mount on system without regular 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). nouser Forbid an ordinary (i.e., non-root) user to mount the filesystem. This is the default; it does not imply any other options. users 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). x-* All options prefixed with "x-" are interpreted as comments or userspace application-specific options. These options are not stored in the mtab file, nor sent to the mount. helpers nor the mount(2) system call. The suggested format is x-.