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

       mount - mount filesystem

       #include <sys/mount.h>

       int mount(const char *source, const char *target,
		 const char *filesystemtype, unsigned long mountflags,
		 const void *data);

       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).)

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

	      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.

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

	      Do not allow access to devices (special files) on this  filesys‐

	      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 when executing
	      programs from this filesystem.

	      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.

	      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 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_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

       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

       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.

       On  success,  zero is returned.	On error, -1 is returned, and errno is
       set appropriately.

       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

       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

	      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.

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

	      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.

       The  definitions	 of  MS_DIRSYNC,  MS_MOVE,  MS_REC,  MS_RELATIME,  and
       MS_STRICTATIME were added to glibc headers in version 2.12.

       This  function  is  Linux-specific  and	should not be used in programs
       intended to be portable.

       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	names‐
       paces.  A mount namespace is the set of filesystem mounts that are vis‐
       ible 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.

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

       This  page  is  part of release 3.65 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at

Linux				  2014-03-17			      MOUNT(2)

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