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

       umount, umount2 - unmount file system

       #include <sys/mount.h>

       int umount(const char *target);

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

       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

       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.

       On success, zero is returned.  On error, -1 is returned, and errno is set appropriately.

       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.

       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

              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.

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

       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).

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

       This  page  is part of release 3.22 of the Linux man-pages project.  A description of the project, and informa-
       tion about reporting bugs, can be found at

Linux                             2008-10-06                         UMOUNT(2)