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NAME

       umount, umount2 - unmount file system

SYNOPSIS

       #include <sys/mount.h>

       int umount(const char *target);

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

DESCRIPTION

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

       Appropriate privilege (Linux: the CAP_SYS_ADMIN capability) is required
       to unmount file systems.

       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.

       UMOUNT_NOFOLLOW (since Linux 2.6.34)
              Don't dereference target if it is a symbolic  link.   This  flag
              allows  security  problems  to  be  avoided  in set-user-ID-root
              programs that allow unprivileged users to unmount file systems.

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 file-system 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.

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

       EBUSY  target could not be unmounted because it is busy.

       EFAULT target points outside the user address space.

       EINVAL target is not a mount point.   Or,  umount2()  was  called  with
              MNT_EXPIRE and either MNT_DETACH or MNT_FORCE.

       ENAMETOOLONG
              A pathname was longer than MAXPATHLEN.

       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.

       EPERM  The caller does not have the required privileges.

VERSIONS

       MNT_DETACH and MNT_EXPIRE are only available  in  glibc  since  version
       2.11.

CONFORMING TO

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

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).

SEE ALSO

       mount(2), path_resolution(7), mount(8), umount(8)

COLOPHON

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