|MOUNT(2)||Linux Programmer's Manual||MOUNT(2)|
NAME¶mount - mount filesystem
#include <sys/mount.h>int mount(const char *source, const char *target, const char *filesystemtype, unsigned long mountflags, const void *data);
DESCRIPTION¶mount() attaches the filesystem specified by source (which is often a pathname referring to a device, but can also be the pathname of a directory or file, or a dummy string) to the location (a directory or file) specified by the pathname in target.
- Remount an existing mount: mountflags includes MS_REMOUNT.
- Create a bind mount: mountflags includes MS_BIND.
- Change the propagation type of an existing mount: mountflags includes one of MS_SHARED, MS_PRIVATE, MS_SLAVE, or MS_UNBINDABLE.
- Move an existing mount to a new location: mountflags includes MS_MOVE.
- Create a new mount: mountflags includes none of the above flags.
Additional mount flags¶The list below describes the additional flags that can be specified in mountflags. Note that some operation types ignore some or all of these flags, as described later in this page.
- MS_DIRSYNC (since Linux 2.5.19)
- Make directory changes on this filesystem synchronous. (This property can be obtained for individual directories or subtrees using chattr(1).)
- MS_LAZYTIME (since Linux 4.0)
- Reduce on-disk updates of inode timestamps (atime, mtime, ctime) by maintaining these changes only in memory. The on-disk timestamps are updated only when:
- the inode needs to be updated for some change unrelated to file timestamps;
- an undeleted inode is evicted from memory; or
- more than 24 hours have passed since the inode was written to disk.
- This mount option significantly reduces writes needed to
update the inode's timestamps, especially mtime and atime. However, in the
event of a system crash, the atime and mtime fields on disk might be out
of date by up to 24 hours.
- Permit mandatory locking on files in this filesystem. (Mandatory locking must still be enabled on a per-file basis, as described in fcntl(2).) Since Linux 4.5, this mount option requires the CAP_SYS_ADMIN capability.
- Do not update access times for (all types of) files on this filesystem.
- Do not allow access to devices (special files) on this filesystem.
- Do not update access times for directories on this filesystem. This flag provides a subset of the functionality provided by MS_NOATIME; that is, MS_NOATIME implies MS_NODIRATIME.
- Do not allow programs to be executed from this filesystem.
- Do not honor set-user-ID and set-group-ID bits or file capabilities when executing programs from this filesystem.
- Mount filesystem read-only.
- MS_REC (since Linux 2.4.11)
- Used in conjunction with MS_BIND to create a recursive bind mount, and in conjunction with the propagation type flags to recursively change the propagation type of all of the mounts in a subtree. See below for further details.
- MS_RELATIME (since Linux 2.6.20)
- When a file on this filesystem is accessed, update the file's last access time (atime) only if the current value of atime is less than or equal to the file's last modification time (mtime) or last status change time (ctime). This option is useful for programs, such as mutt(1), that need to know when a file has been read since it was last modified. Since Linux 2.6.30, the kernel defaults to the behavior provided by this flag (unless MS_NOATIME was specified), and the MS_STRICTATIME flag 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.
- MS_SILENT (since Linux 2.6.17)
- Suppress the display of certain (printk()) warning messages in the kernel log. This flag supersedes the misnamed and obsolete MS_VERBOSE flag (available since Linux 2.4.12), which has the same meaning.
- MS_STRICTATIME (since Linux 2.6.30)
- Always update the last access time (atime) when files on this filesystem are accessed. (This was the default behavior before Linux 2.6.30.) Specifying this flag overrides the effect of setting the MS_NOATIME and MS_RELATIME flags.
- Make writes on this filesystem synchronous (as though the O_SYNC flag to open(2) was specified for all file opens to this filesystem).
Remounting an existing mount¶An existing mount may be remounted by specifying MS_REMOUNT in mountflags. This allows you to change the mountflags and data of an existing mount without having to unmount and remount the filesystem. target should be the same value specified in the initial mount() call.
MS_REMOUNT | MS_BIND | MS_RDONLY
Creating a bind mount¶If mountflags includes MS_BIND (available since Linux 2.4), then perform a bind mount. A bind mount makes a file or a directory subtree visible at another point within the single directory hierarchy. Bind mounts may cross filesystem boundaries and span chroot(2) jails.
Changing the propagation type of an existing mount¶If mountflags includes one of MS_SHARED, MS_PRIVATE, MS_SLAVE, or MS_UNBINDABLE (all available since Linux 2.6.15), then the propagation type of an existing mount is changed. If more than one of these flags is specified, an error results.
- Make this mount point shared. Mount and unmount events immediately under this mount point will propagate to the other mount points that are members of this mount's peer group. Propagation here means that the same mount or unmount will automatically occur under all of the other mount points in the peer group. Conversely, mount and unmount events that take place under peer mount points will propagate to this mount point.
- Make this mount point private. Mount and unmount events do not propagate into or out of this mount point.
- If this is a shared mount point that is a member of a peer
group that contains other members, convert it to a slave mount. If this is
a shared mount point that is a member of a peer group that contains no
other members, convert it to a private mount. Otherwise, the propagation
type of the mount point is left unchanged.
- Make this mount unbindable. This is like a private mount, and in addition this mount can't be bind mounted. When a recursive bind mount (mount() with the MS_BIND and MS_REC flags) is performed on a directory subtree, any bind mounts within the subtree are automatically pruned (i.e., not replicated) when replicating that subtree to produce the target subtree.
Moving a mount¶If mountflags contains the flag MS_MOVE (available since Linux 2.4.18), then move a subtree: source specifies an existing mount point and target specifies the new location to which that mount point is to be relocated. The move is atomic: at no point is the subtree unmounted.
Creating a new mount point¶If none of MS_REMOUNT, MS_BIND, MS_MOVE, MS_SHARED, MS_PRIVATE, MS_SLAVE, or MS_UNBINDABLE is specified in mountflags, then mount() performs its default action: creating a new mount point. source specifies the source for the new mount point, and target specifies the directory at which to create the mount point.
RETURN VALUE¶On success, zero is returned. On error, -1 is returned, and errno is set appropriately.
ERRORS¶The error values given below result from filesystem type independent errors. Each filesystem type may have its own special errors and its own special behavior. See the Linux kernel source code for details.
- A component of a path was not searchable. (See also path_resolution(7).)
- Mounting a read-only filesystem was attempted without giving the MS_RDONLY flag.
- The block device source is located on a filesystem mounted with the MS_NODEV option.
- source is already mounted.
- source cannot be remounted read-only, because it still holds files open for writing.
- source cannot be mounted on target because target is still busy (it is the working directory of some thread, the mount point of another device, has open files, etc.).
- One of the pointer arguments points outside the user address space.
- source had an invalid superblock.
- A remount operation (MS_REMOUNT) was attempted, but source was not already mounted on target.
- A move operation (MS_MOVE) was attempted, but source was not a mount point, or was '/'.
- mountflags includes more than one of MS_SHARED, MS_PRIVATE, MS_SLAVE, or MS_UNBINDABLE.
- mountflags includes MS_SHARED, MS_PRIVATE, MS_SLAVE, or MS_UNBINDABLE and also includes a flag other than MS_REC or MS_SILENT.
- An attempt was made to bind mount an unbindable mount.
- Too many links encountered during pathname resolution.
- A move operation was attempted, and target is a descendant of source.
- (In case no block device is required:) Table of dummy devices is full.
- A pathname was longer than MAXPATHLEN.
- filesystemtype not configured in the kernel.
- A pathname was empty or had a nonexistent component.
- The kernel could not allocate a free page to copy filenames or data into.
- source is not a block device (and a device was required).
- target, or a prefix of source, is not a directory.
- The major number of the block device source is out of range.
- The caller does not have the required privileges.
VERSIONS¶The definitions of MS_DIRSYNC, MS_MOVE, MS_PRIVATE, MS_REC, MS_RELATIME, MS_SHARED, MS_SLAVE, MS_STRICTATIME and MS_UNBINDABLE were added to glibc headers in version 2.12.
CONFORMING TO¶This function is Linux-specific and should not be used in programs intended to be portable.
NOTES¶Since Linux 2.4 a single filesystem can be mounted at multiple mount points, and multiple mounts can be stacked on the same mount point.
Per-process namespaces¶Starting with kernel 2.4.19, Linux provides per-process mount namespaces. A mount namespace is the set of filesystem mounts that are visible to a process. Mount-point namespaces can be (and usually are) shared between multiple processes, and changes to the namespace (i.e., mounts and unmounts) by one process are visible to all other processes sharing the same namespace. (The pre-2.4.19 Linux situation can be considered as one in which a single namespace was shared by every process on the system.)
SEE ALSO¶mountpoint(1), umount(2), mount_namespaces(7), path_resolution(7), findmnt(8), lsblk(8), mount(8), umount(8)
COLOPHON¶This page is part of release 4.10 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.