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

       mount - mount file system

       #include <sys/mount.h>

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

       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 appro-
       priate 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 system.   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).)

              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).)

              Move a subtree.  source specifies an existing mount point and target  speci-
              fies  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 file system.

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

              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.

              Do not allow programs to be executed from this file system.

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

              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 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  mountflags  and
              data  of  an  existing  mount without having to unmount and remount the file
              system.  source and target should be the same values specified in  the  ini-
              tial mount() call; filesystemtype is ignored.

              The following mountflags can be changed: MS_RDONLY, MS_SYNCHRONOUS, MS_MAND-
              LOCK; 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 (avail-
              able 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.)  Speci-
              fying this flag overrides the effect of setting the MS_NOATIME and  MS_RELA-
              TIME flags.

              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_NODIRA-
       TIME 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.

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

       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.

              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.

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

       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.

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

       This page is part of release 3.22 of the Linux man-pages project.  A description of
       the project, and information about reporting bugs, can be found at  http://www.ker-

Linux                             2009-06-26                          MOUNT(2)

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