Ubuntu Manpage: mount - mount filesystem

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NAME

       mount - mount filesystem

SYNOPSIS

       #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 device name, but can
also be a directory name or a dummy) to the directory specified by target.

Appropriate privilege (Linux: the CAP_SYS_ADMIN capability) is required to mount
filesystems.

Since Linux 2.4 a single filesystem can be visible at multiple mount points, and multiple
mounts can be stacked on the same mount point.

Values for the filesystemtype argument supported by the kernel are listed in
/proc/filesystems (e.g., "minix", "ext2", "ext3", "jfs", "xfs", "reiserfs", "msdos",
"proc", "nfs", "iso9660"). Further types may become available when the appropriate
modules are loaded.

The mountflags argument may have the magic number 0xC0ED (MS_MGC_VAL) in the top 16 bits
(this was required in kernel versions prior to 2.4, but is no longer required and ignored
if specified), and various mount flags in the low order 16 bits:

MS_BIND (Linux 2.4 onward)
Perform a bind mount, making a file or a directory subtree visible at another point
within a filesystem. Bind mounts may cross filesystem boundaries and span
chroot(2) jails. The filesystemtype and data arguments are ignored. Up until
Linux 2.6.26, mountflags was also ignored (the bind mount has the same mount
options as the underlying mount point).

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_MANDLOCK
Permit mandatory locking on files in this filesystem. (Mandatory locking must
still be enabled on a per-file basis, as described in fcntl(2).)

MS_MOVE
Move a subtree. source specifies an existing mount point and target specifies the
new location. The move is atomic: at no point is the subtree unmounted. The
filesystemtype, mountflags, and data arguments are ignored.

MS_NOATIME
Do not update access times for (all types of) files on this filesystem.

MS_NODEV
Do not allow access to devices (special files) on this filesystem.

MS_NODIRATIME
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.

MS_NOEXEC
Do not allow programs to be executed from this filesystem.

MS_NOSUID
Do not honor set-user-ID and set-group-ID bits when executing programs from this
filesystem.

MS_RDONLY
Mount filesystem read-only.

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_REMOUNT
Remount an existing mount. 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; source and filesystemtype
are ignored.

The following mountflags can be changed: MS_RDONLY, MS_SYNCHRONOUS, MS_MANDLOCK;
before kernel 2.6.16, the following could also be changed: MS_NOATIME and
MS_NODIRATIME; and, additionally, before kernel 2.4.10, the following could also be
changed: MS_NOSUID, MS_NODEV, MS_NOEXEC.

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.

MS_SYNCHRONOUS
Make writes on this filesystem synchronous (as though the O_SYNC flag to open(2)
was specified for all file opens to this filesystem).

From Linux 2.4 onward, the MS_NODEV, MS_NOEXEC, and MS_NOSUID flags are settable on a per-
mount-point basis. From kernel 2.6.16 onward, MS_NOATIME and MS_NODIRATIME are also
settable on a per-mount-point basis. The MS_RELATIME flag is also settable on a per-
mount-point basis.

The data argument is interpreted by the different filesystems. Typically it is a string
of comma-separated options understood by this filesystem. See mount(8) for details of the
options available for each filesystem type.

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.

EACCES A component of a path was not searchable. (See also path_resolution(7).) Or,
mounting a read-only filesystem was attempted without giving the MS_RDONLY flag.
Or, the block device source is located on a filesystem mounted with the MS_NODEV
option.

EBUSY source is already mounted. Or, it cannot be remounted read-only, because it still
holds files open for writing. Or, it 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.).

EFAULT One of the pointer arguments points outside the user address space.

EINVAL source had an invalid superblock. Or, a remount (MS_REMOUNT) was attempted, but
source was not already mounted on target. Or, a move (MS_MOVE) was attempted, but
source was not a mount point, or was '/'.

ELOOP Too many links encountered during pathname resolution. Or, a move was attempted,
while target is a descendant of source.

EMFILE (In case no block device is required:) Table of dummy devices is full.

ENAMETOOLONG
A pathname was longer than MAXPATHLEN.

ENODEV filesystemtype not configured in the kernel.

ENOENT A pathname was empty or had a nonexistent component.

ENOMEM The kernel could not allocate a free page to copy filenames or data into.

ENOTBLK
source is not a block device (and a device was required).

ENOTDIR
target, or a prefix of source, is not a directory.

ENXIO The major number of the block device source is out of range.

EPERM The caller does not have the required privileges.

VERSIONS

       The definitions of MS_DIRSYNC, MS_MOVE, MS_REC, MS_RELATIME, and MS_STRICTATIME 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

       The  original  MS_SYNC  flag was renamed MS_SYNCHRONOUS in 1.1.69 when a different MS_SYNC
       was added to <mman.h>.

       Before Linux 2.4 an attempt  to  execute  a  set-user-ID  or  set-group-ID  program  on  a
       filesystem  mounted with MS_NOSUID would fail with EPERM.  Since Linux 2.4 the set-user-ID
       and set-group-ID bits are just silently ignored in this case.

   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.)

       A  child  process  created  by  fork(2)  shares  its  parent's  mount namespace; the mount
       namespace is preserved across an execve(2).

       A process can obtain a private mount namespace if:  it  was  created  using  the  clone(2)
       CLONE_NEWNS  flag,  in  which  case  its  new namespace is initialized to be a copy of the
       namespace of the process that called clone(2); or it calls unshare(2) with the CLONE_NEWNS
       flag,  which causes the caller's mount namespace to obtain a private copy of the namespace
       that it was previously sharing with other processes, so that future mounts and unmounts by
       the  caller  are  invisible  to  other  processes  (except child processes that the caller
       subsequently creates) and vice versa.

       The Linux-specific /proc/PID/mounts file exposes the list of mount  points  in  the  mount
       namespace of the process with the specified ID; see proc(5) for details.

COLOPHON

       This  page  is  part of release 3.54 of the Linux man-pages project.  A description of the
       project,    and    information    about    reporting    bugs,    can    be    found     at
       http://www.kernel.org/doc/man-pages/.