umount2 man page on Debian

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

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 sys‐
       tem 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  cur‐
	      rently  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 pro‐
	      grams 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
       This  page  is  part of release 3.27 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/.

Linux				  2010-06-19			     UMOUNT(2)
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