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

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	direc-
       tory 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 visi-
	      ble at another point within a filesystem.	 Bind mounts may cross
	      filesystem boundaries and	span chroot(2) jails.  The filesystem-
	      type 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.   (Manda-
	      tory  locking  must still	be enabled on a	per-file basis,	as de-
	      scribed 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  filesys-
	      tem.

       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 re-
	      quired 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	mount-
	      flags  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	mountflags and data arguments should match the
	      values  used  in the original mount() call, except for those pa-
	      rameters that are	being deliberately changed.

	      The following mountflags can be changed: MS_RDONLY,  MS_SYNCHRO-
	      NOUS,  MS_MANDLOCK;  before  kernel  2.6.16, the following could
	      also be changed: MS_NOATIME and  MS_NODIRATIME;  and,  addition-
	      ally, 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 ba-
       sis.  The MS_RELATIME flag is also settable on a	per-mount-point	basis.

       The  data  argument is interpreted by the different filesystems.	 Typi-
       cally 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_reso-
	      lution(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  in-
       tended 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 name-
       spaces.	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  ini-
       tialized	 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 pro-
       cesses (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.

SEE ALSO
       lsblk(1),   umount(2),	namespaces(7),	path_resolution(7),  mount(8),
       umount(8)

COLOPHON
       This page is part of release 3.74 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
       http://www.kernel.org/doc/man-pages/.

Linux				  2014-09-21			      MOUNT(2)

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | CONFORMING TO | NOTES | SEE ALSO | COLOPHON

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