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