mount


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
              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
       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 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_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
       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
       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.

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

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/.



Linux                             2012-07-05                          MOUNT(2)
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