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



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 tar‐
       get.

       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 prob‐
              lems  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.

       EINVAL umount2() was called with MNT_EXPIRE and either MNT_DETACH or MNT_FORCE.

       EINVAL (since Linux 2.6.34)
              umount2() was called with an invalid flag value in flags.

       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 por‐
       table.

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 3.74 of the Linux man-pages project.  A  description  of  the
       project,  information  about  reporting  bugs, and the latest version of this page, can be
       found at http://www.kernel.org/doc/man-pages/.



Linux                                       2014-02-26                                  UMOUNT(2)