337 lines
7.5 KiB
HTML
337 lines
7.5 KiB
HTML
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<HTML><HEAD><TITLE>Man page of UMOUNT</TITLE>
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</HEAD><BODY>
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<H1>UMOUNT</H1>
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Section: Linux Programmer's Manual (2)<BR>Updated: 2017-09-15<BR><A HREF="#index">Index</A>
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<A HREF="/cgi-bin/man/man2html">Return to Main Contents</A><HR>
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<A NAME="lbAB"> </A>
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<H2>NAME</H2>
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umount, umount2 - unmount filesystem
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<A NAME="lbAC"> </A>
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<H2>SYNOPSIS</H2>
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<PRE>
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<B>#include <<A HREF="file:///usr/include/sys/mount.h">sys/mount.h</A>></B>
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<B>int umount(const char *</B><I>target</I><B>);</B>
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<B>int umount2(const char *</B><I>target</I><B>, int </B><I>flags</I><B>);</B>
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</PRE>
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<A NAME="lbAD"> </A>
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<H2>DESCRIPTION</H2>
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<B>umount</B>()
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and
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<B>umount2</B>()
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remove the attachment of the (topmost) filesystem mounted on
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<I>target</I>.
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<P>
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Appropriate privilege (Linux: the
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<B>CAP_SYS_ADMIN</B>
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capability) is required to unmount filesystems.
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<P>
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Linux 2.1.116 added the
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<B>umount2</B>()
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system call, which, like
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<B>umount</B>(),
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unmounts a target, but allows additional
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<I>flags</I>
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controlling the behavior of the operation:
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<DL COMPACT>
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<DT id="1"><B>MNT_FORCE</B> (since Linux 2.1.116)
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<DD>
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Ask the filesystem to abort pending requests before attempting the
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unmount.
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This may allow the unmount to complete without waiting
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for an inaccessible server, but could cause data loss.
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If, after aborting requests,
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some processes still have active references to the filesystem,
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the unmount will still fail.
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As at Linux 4.12,
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<B>MNT_FORCE</B>
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is supported only on the following filesystems:
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9p (since Linux 2.6.16),
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ceph (since Linux 2.6.34),
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cifs (since Linux 2.6.12),
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fuse (since Linux 2.6.16),
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lustre (since Linux 3.11),
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and NFS (since Linux 2.1.116).
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<DT id="2"><B>MNT_DETACH</B> (since Linux 2.4.11)
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<DD>
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Perform a lazy unmount: make the mount point unavailable for new
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accesses, immediately disconnect the filesystem and all filesystems
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mounted below it from each other and from the mount table, and
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actually perform the unmount when the mount point ceases to be busy.
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<DT id="3"><B>MNT_EXPIRE</B> (since Linux 2.6.8)
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<DD>
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Mark the mount point as expired.
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If a mount point is not currently in use, then an initial call to
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<B>umount2</B>()
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with this flag fails with the error
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<B>EAGAIN</B>,
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but marks the mount point as expired.
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The mount point remains expired as long as it isn't accessed
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by any process.
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A second
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<B>umount2</B>()
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call specifying
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<B>MNT_EXPIRE</B>
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unmounts an expired mount point.
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This flag cannot be specified with either
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<B>MNT_FORCE</B>
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or
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<B>MNT_DETACH</B>.
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<DT id="4"><B>UMOUNT_NOFOLLOW</B> (since Linux 2.6.34)
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<DD>
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Don't dereference
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<I>target</I>
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if it is a symbolic link.
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This flag allows security problems to be avoided in set-user-ID-<I>root</I>
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programs that allow unprivileged users to unmount filesystems.
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</DL>
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<A NAME="lbAE"> </A>
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<H2>RETURN VALUE</H2>
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On success, zero is returned.
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On error, -1 is returned, and
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<I>errno</I>
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is set appropriately.
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<A NAME="lbAF"> </A>
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<H2>ERRORS</H2>
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The error values given below result from filesystem type independent
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errors.
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Each filesystem type may have its own special errors and its
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own special behavior.
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See the Linux kernel source code for details.
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<DL COMPACT>
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<DT id="5"><B>EAGAIN</B>
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<DD>
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A call to
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<B>umount2</B>()
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specifying
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<B>MNT_EXPIRE</B>
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successfully marked an unbusy filesystem as expired.
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<DT id="6"><B>EBUSY</B>
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<DD>
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<I>target</I>
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could not be unmounted because it is busy.
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<DT id="7"><B>EFAULT</B>
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<DD>
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<I>target</I>
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points outside the user address space.
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<DT id="8"><B>EINVAL</B>
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<DD>
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<I>target</I>
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is not a mount point.
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<DT id="9"><B>EINVAL</B>
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<DD>
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<B>umount2</B>()
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was called with
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<B>MNT_EXPIRE</B>
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and either
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<B>MNT_DETACH</B>
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or
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<B>MNT_FORCE</B>.
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<DT id="10"><B>EINVAL</B> (since Linux 2.6.34)
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<DD>
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<B>umount2</B>()
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was called with an invalid flag value in
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<I>flags</I>.
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<DT id="11"><B>ENAMETOOLONG</B>
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<DD>
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A pathname was longer than
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<B>MAXPATHLEN</B>.
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<DT id="12"><B>ENOENT</B>
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<DD>
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A pathname was empty or had a nonexistent component.
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<DT id="13"><B>ENOMEM</B>
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<DD>
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The kernel could not allocate a free page to copy filenames or data into.
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<DT id="14"><B>EPERM</B>
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<DD>
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The caller does not have the required privileges.
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</DL>
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<A NAME="lbAG"> </A>
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<H2>VERSIONS</H2>
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<B>MNT_DETACH</B>
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and
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<B>MNT_EXPIRE</B>
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are available in glibc since version 2.11.
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<A NAME="lbAH"> </A>
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<H2>CONFORMING TO</H2>
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These functions are Linux-specific and should not be used in
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programs intended to be portable.
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<A NAME="lbAI"> </A>
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<H2>NOTES</H2>
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<A NAME="lbAJ"> </A>
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<H3>umount() and shared mount points</H3>
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Shared mount points cause any mount activity on a mount point, including
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<B>umount</B>()
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operations, to be forwarded to every shared mount point in the
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peer group and every slave mount of that peer group.
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This means that
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<B>umount</B>()
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of any peer in a set of shared mounts will cause all of its
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peers to be unmounted and all of their slaves to be unmounted as well.
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<P>
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This propagation of unmount activity can be particularly surprising
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on systems where every mount point is shared by default.
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On such systems,
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recursively bind mounting the root directory of the filesystem
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onto a subdirectory and then later unmounting that subdirectory with
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<B>MNT_DETACH</B>
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will cause every mount in the mount namespace to be lazily unmounted.
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<P>
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To ensure
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<B>umount</B>()
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does not propagate in this fashion,
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the mount point may be remounted using a
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<B>mount</B>()
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call with a
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<I>mount_flags</I>
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argument that includes both
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<B>MS_REC</B>
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and
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<B>MS_PRIVATE</B>
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prior to
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<B>umount</B>()
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being called.
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<A NAME="lbAK"> </A>
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<H3>Historical details</H3>
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The original
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<B>umount</B>()
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function was called as <I>umount(device)</I> and would return
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<B>ENOTBLK</B>
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when called with something other than a block device.
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In Linux 0.98p4, a call <I>umount(dir)</I> was added, in order to
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support anonymous devices.
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In Linux 2.3.99-pre7, the call <I>umount(device)</I> was removed,
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leaving only <I>umount(dir)</I> (since now devices can be mounted
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in more than one place, so specifying the device does not suffice).
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<A NAME="lbAL"> </A>
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<H2>SEE ALSO</H2>
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<B><A HREF="/cgi-bin/man/man2html?2+mount">mount</A></B>(2),
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<B><A HREF="/cgi-bin/man/man2html?7+mount_namespaces">mount_namespaces</A></B>(7),
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<B><A HREF="/cgi-bin/man/man2html?7+path_resolution">path_resolution</A></B>(7),
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<B><A HREF="/cgi-bin/man/man2html?8+mount">mount</A></B>(8),
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<B><A HREF="/cgi-bin/man/man2html?8+umount">umount</A></B>(8)
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<A NAME="lbAM"> </A>
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<H2>COLOPHON</H2>
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This page is part of release 5.05 of the Linux
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<I>man-pages</I>
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project.
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A description of the project,
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information about reporting bugs,
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and the latest version of this page,
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can be found at
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<A HREF="https://www.kernel.org/doc/man-pages/.">https://www.kernel.org/doc/man-pages/.</A>
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<P>
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<HR>
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<A NAME="index"> </A><H2>Index</H2>
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<DL>
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<DT id="15"><A HREF="#lbAB">NAME</A><DD>
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<DT id="16"><A HREF="#lbAC">SYNOPSIS</A><DD>
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<DT id="17"><A HREF="#lbAD">DESCRIPTION</A><DD>
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<DT id="18"><A HREF="#lbAE">RETURN VALUE</A><DD>
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<DT id="19"><A HREF="#lbAF">ERRORS</A><DD>
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<DT id="20"><A HREF="#lbAG">VERSIONS</A><DD>
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<DT id="21"><A HREF="#lbAH">CONFORMING TO</A><DD>
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<DT id="22"><A HREF="#lbAI">NOTES</A><DD>
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<DL>
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<DT id="23"><A HREF="#lbAJ">umount() and shared mount points</A><DD>
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<DT id="24"><A HREF="#lbAK">Historical details</A><DD>
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</DL>
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<DT id="25"><A HREF="#lbAL">SEE ALSO</A><DD>
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<DT id="26"><A HREF="#lbAM">COLOPHON</A><DD>
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</DL>
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<HR>
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This document was created by
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<A HREF="/cgi-bin/man/man2html">man2html</A>,
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using the manual pages.<BR>
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Time: 00:05:35 GMT, March 31, 2021
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</BODY>
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</HTML>
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