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MOUNT(2)                   Linux Programmer's Manual                  MOUNT(2)



NAME
       mount - mount file system

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 file system 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 file systems.

       Since Linux 2.4 a single file system 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 (like "minix",
       "ext2", "ext3", "jfs", "xfs", "reiserfs", "msdos", "proc", "nfs", "iso9660" etc.).  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  (as
       defined in <linux/fs.h> for libc4 and libc5 and in <sys/mount.h> for glibc2) in the low order 16 bits:

       MS_BIND (Linux 2.4 onwards)
              Perform  a  bind mount, making a file or a directory subtree visible at another point within a file sys-
              tem.  Bind mounts may cross file system 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).  Since Linux 2.6.26, the MS_RDONLY  flag  is  honored
              when making a bind mount.

       MS_DIRSYNC (since Linux 2.5.19)
              Make  directory  changes on this file system synchronous.  (This property can be obtained for individual
              directories or subtrees using chattr(1).)

       MS_MANDLOCK
              Permit mandatory locking on files in this file system.  (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  argu-
              ments are ignored.

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

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

       MS_NODIRATIME
              Do  not  update  access  times  for directories on this file system.  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 file system.

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

       MS_RDONLY
              Mount file system read-only.

       MS_RELATIME (Since Linux 2.6.20)
              When a file on this file system is accessed, only update the file's last access time (atime) if the cur-
              rent  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 pro-
              vided 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 with-
              out  having  to unmount and remount the file system.  source and target should be the same values speci-
              fied in the initial mount() call; filesystemtype is 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 file system are accessed.  (This was the
              default behavior before Linux 2.6.30.)  Specifying this flag overrides the effect of setting the MS_NOA-
              TIME and MS_RELATIME flags.

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

       From Linux 2.4 onwards, the MS_NODEV, MS_NOEXEC, and MS_NOSUID flags are settable on a  per-mount-point  basis.
       From  kernel  2.6.16  onwards,  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 file systems.  Typically it is a  string  of  comma-separated
       options  understood by this file system.  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 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 task, 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.

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 file
       system  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
       there was 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() CLONE_NEWNS flag, in which
       case its new namespace is initialized to be a copy of the namespace of the process that called clone();  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/self file exposes the list of mount points in the mount namespace of  the  process
       with the specified ID; see proc(5) for details.

SEE ALSO
       umount(2), path_resolution(7), mount(8), umount(8)

COLOPHON
       This  page  is part of release 3.22 of the Linux man-pages project.  A description of the project, and informa-
       tion about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



Linux                             2009-06-26                          MOUNT(2)