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

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

       This  page is part of release 3.35 of the Linux man-pages project.  A description of the project, and information about reporting bugs,
       can be found at http://man7.org/linux/man-pages/.
 

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