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NAME

       mount - mount file system

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  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  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 (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 onward)
              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).)

       MS_MANDLOCK
              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).)

       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 file system.

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

       MS_NODIRATIME
              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.

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

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

       MS_RDONLY
              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.

       MS_REMOUNT
              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  initial  mount()   call;
              filesystemtype is ignored.

              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_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 (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  file  system  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 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 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 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.

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  file-
       system  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 file system was attempted without giving the MS_RDONLY flag.
              Or, the block device source is located on a file system 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 only
       added to glibc headers in version 2.12.

CONFORMING TO

       This function is Linux-specific and  should  not  be  used  in  programs  intended  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  file
       system  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 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 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
       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), path_resolution(7), mount(8), umount(8)

COLOPHON

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       project, and information about reporting bugs, can be found at  http://man7.org/linux/man-
       pages/.