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NAME

       mount, umount, umount2 - mount and unmount filesystems

SYNOPSIS

       #include <sys/mount.h>

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

       int umount(const char *target);

       int umount2(const char *target, int flags);

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
       directory specified by target.

       umount()   and   umount2()  remove  the  attachment  of  the  (topmost)
       filesystem mounted on target.

       Appropriate privilege (Linux: the CAP_SYS_ADMIN capability) is required
       to mount and unmount 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  (like  "minix", "ext2", "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 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, mountflags, and data arguments are ignored.

       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 accessed time (atime) if the current value of atime
              is less than or equal to the file’s  last  modified  (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.

       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, the  following  could  also  be
              changed: MS_NOSUID, MS_NODEV, MS_NOEXEC.

       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  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_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.

       Linux 2.1.116 added the umount2() system call,  which,  like  umount(),
       unmounts a target, but allows additional flags controlling the behavior
       of the operation:

       MNT_FORCE (since Linux 2.1.116)
              Force unmount even if busy.  This can cause  data  loss.   (Only
              for NFS mounts.)

       MNT_DETACH (since Linux 2.4.11)
              Perform a lazy unmount: make the mount point unavailable for new
              accesses, and actually perform the unmount when the mount  point
              ceases to be busy.

       MNT_EXPIRE (since Linux 2.6.8)
              Mark  the  mount  point  as  expired.   If  a mount point is not
              currently in use, then an initial call to  umount2()  with  this
              flag  fails  with the error EAGAIN, but marks the mount point as
              expired.  The mount point remains expired as long  as  it  isn’t
              accessed  by  any  process.   A second umount2() call specifying
              MNT_EXPIRE unmounts an expired mount point.  This flag cannot be
              specified with either MNT_FORCE or MNT_DETACH.

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  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.

       EAGAIN A call to umount2() specifying MNT_EXPIRE successfully marked an
              unbusy file system as expired.

       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.).  Or, it could not be unmounted
              because it is busy.

       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 ’/’.  Or, an unmount was attempted, but target was
              not a mount point.  Or, umount2() was called with MNT_EXPIRE and
              either MNT_DETACH or MNT_FORCE.

       ELOOP  Too many link 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
              The second argument, or a prefix of the first argument, 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.

CONFORMING TO

       These functions are Linux-specific and should not be used  in  programs
       intended to be portable.

NOTES

   Linux Notes
       The  original  umount() function was called as umount(device) and would
       return ENOTBLK when called with something other than  a  block  device.
       In  Linux  0.98p4  a  call  umount(dir)  was added, in order to support
       anonymous devices.  In Linux 2.3.99-pre7 the  call  umount(device)  was
       removed,  leaving only umount(dir) (since now devices can be mounted in
       more than one place, so specifying the device does not suffice).

       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.

SEE ALSO

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

COLOPHON

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