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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 tar-

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

       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 prob-
              lems  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 file-system type independent errors.   Each  file
       system  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 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.

              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.

       MNT_DETACH and MNT_EXPIRE are available in glibc since version 2.11.

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

       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 3.53 of the Linux man-pages project.  A description of the
       project,    and    information    about    reporting    bugs,    can    be    found     at

Linux                                       2010-06-19                                  UMOUNT(2)

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