NAME

       umount, umount2 - unmount filesystem

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) filesystem mounted on target.

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

       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 filesystems.

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 Linux kernel source code for details.

       EAGAIN A call to umount2() specifying MNT_EXPIRE successfully marked an unbusy filesystem 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 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

       This  page  is  part  of  release 3.54 of the Linux man-pages project.  A description of the project, and
       information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.