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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 directory specified by target.

       Appropriate privilege (Linux: the CAP_SYS_ADMIN capability) is required to mount  filesys‐

       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  mod‐
       ules 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 visible at another point
              within a  filesystem.   Bind  mounts  may  cross  filesystem  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).

       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.   (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 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 filesystem.

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

              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

              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

              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  use‐
              ful  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  behav‐
              ior 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 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 parameters that are being deliberately

              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_NODI‐
              RATIME; 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 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 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 set‐
       table 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 filesystems.  Typically 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_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

       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.

              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 porta‐

       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 filesys‐
       tem 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 names‐
       pace is the set of filesystem mounts that are visible to a  process.   Mount-point  names‐
       paces  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  names‐
       pace 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 initialized  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 processes (except child processes that the caller subse‐
       quently 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), umount(8)

       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)

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