378 lines
11 KiB
HTML
378 lines
11 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: System Administration (8)<BR>Updated: July 2014<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 - unmount file systems
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<A NAME="lbAC"> </A>
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<H2>SYNOPSIS</H2>
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<B>umount -a</B>
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[<B>-dflnrv</B>]
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[<B>-t</B>
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<I>fstype</I>]
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[<B>-O</B>
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<I>option</I>...]
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<P>
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<B>umount</B>
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[<B>-dflnrv</B>]
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{<I>directory</I>|<I>device</I>}...
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<P>
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<B>umount</B>
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<B>-h</B>|<B>-V</B>
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<P>
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<A NAME="lbAD"> </A>
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<H2>DESCRIPTION</H2>
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The
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<B>umount</B>
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command detaches the mentioned file system(s) from the file hierarchy. A
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file system is specified by giving the directory where it has been
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mounted. Giving the special device on which the file system lives may
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also work, but is obsolete, mainly because it will fail in case this
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device was mounted on more than one directory.
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<P>
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Note that a file system cannot be unmounted when it is 'busy' - for
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example, when there are open files on it, or when some process has its
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working directory there, or when a swap file on it is in use. The
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offending process could even be
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<B>umount</B>
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itself - it opens libc, and libc in its turn may open for example locale
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files. A lazy unmount avoids this problem, but it may introduce another
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issues. See <B>--lazy</B> description below.
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<A NAME="lbAE"> </A>
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<H2>OPTIONS</H2>
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<DL COMPACT>
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<DT id="1"><B>-a</B>,<B> --all</B>
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<DD>
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All of the filesystems described in
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<I>/proc/self/mountinfo</I>
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(or in deprecated /etc/mtab)
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are unmounted, except the proc, devfs, devpts, sysfs, rpc_pipefs and nfsd
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filesystems. This list of the filesystems may be replaced by <B>--types</B>
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umount option.
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<DT id="2"><B>-A</B>,<B> --all-targets</B>
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<DD>
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Unmount all mountpoints in the current namespace for the specified filesystem.
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The filesystem can be specified by one of the mountpoints or the device name (or
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UUID, etc.). When this option is used together with <B>--recursive</B>, then
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all nested mounts within the filesystem are recursively unmounted.
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This option is only supported on systems where /etc/mtab is a symlink
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to /proc/mounts.
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<DT id="3"><B>-c</B>,<B> --no-canonicalize</B>
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<DD>
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Do not canonicalize paths. The paths canonicalization is based on
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<B><A HREF="/cgi-bin/man/man2html?2+stat">stat</A></B>(2)
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and
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<B><A HREF="/cgi-bin/man/man2html?2+readlink">readlink</A></B>(2)
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system calls. These system calls may hang in some cases (for example on NFS if
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server is not available). The option has to be used with canonical path to the
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mount point.
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<P>
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For more details about this option see the
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<B><A HREF="/cgi-bin/man/man2html?8+mount">mount</A></B>(8)
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man page. Note that <B>umount</B> does not pass this option to the
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<B>/sbin/umount.</B><I>type</I>
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helpers.
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<DT id="4"><B>-d</B>,<B> --detach-loop</B>
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<DD>
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When the unmounted device was a loop device, also free this loop
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device. This option is unnecessary for devices initialized by
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<B><A HREF="/cgi-bin/man/man2html?8+mount">mount</A></B>(8),
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in this case "autoclear" functionality is enabled by default.
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<DT id="5"><B>--fake</B>
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<DD>
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Causes everything to be done except for the actual system call or umount helper
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execution; this 'fakes' unmounting the filesystem. It can be used to remove
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entries from the deprecated
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<I>/etc/mtab</I>
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that were unmounted earlier with the
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<B>-n</B>
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option.
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<DT id="6"><B>-f</B>,<B> --force</B>
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<DD>
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Force an unmount (in case of an unreachable NFS system).
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<P>
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Note that this option does not guarantee that umount command does not hang.
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It's strongly recommended to use absolute paths without symlinks to avoid
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unwanted readlink and stat system calls on unreachable NFS in umount.
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<DT id="7"><B>-i</B>,<B> --internal-only</B>
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<DD>
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Do not call the <B>/sbin/umount.</B><I>filesystem</I> helper even if it exists.
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By default such a helper program is called if it exists.
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<DT id="8"><B>-l</B>,<B> --lazy</B>
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<DD>
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Lazy unmount. Detach the filesystem from the file hierarchy now,
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and clean up all references to this filesystem as soon as it is not busy
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anymore.
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<P>
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A system reboot would be expected in near future if you're going to use this
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option for network filesystem or local filesystem with submounts. The
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recommended use-case for <B>umount -l</B> is to prevent hangs on shutdown due to
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an unreachable network share where a normal umount will hang due to a downed
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server or a network partition. Remounts of the share will not be possible.
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<P>
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<DT id="9"><B>-N</B>,<B> --namespace </B><I>ns</I>
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<DD>
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Perform umount in namespace specified by <I>ns</I>.
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<I>ns</I> is either PID of process running in that namespace
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or special file representing that namespace.
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<P>
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<B><A HREF="/cgi-bin/man/man2html?8+umount">umount</A></B>(8)
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switches to the namespace when it reads /etc/fstab, writes /etc/mtab (or writes to /run/mount) and calls
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<B><A HREF="/cgi-bin/man/man2html?2+umount">umount</A></B>(2)
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system call, otherwise it runs in the original namespace. It means that the target namespace does not have
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to contain any libraries or another requirements necessary to execute
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<B><A HREF="/cgi-bin/man/man2html?2+umount">umount</A></B>(2)
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command.
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<P>
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See <B><A HREF="/cgi-bin/man/man2html?7+namespaces">namespaces</A></B>(7) for more information.
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<DT id="10"><B>-n</B>,<B> --no-mtab</B>
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<DD>
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Unmount without writing in
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<I>/etc/mtab</I>.
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<DT id="11"><B>-O</B>,<B> --test-opts </B><I>option</I>...
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<DD>
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Unmount only the filesystems that have the specified option set in
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<I>/etc/fstab</I>.
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More than one option may be specified in a comma-separated list.
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Each option can be prefixed with
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<B>no</B>
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to indicate that no action should be taken for this option.
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<DT id="12"><B>-q</B>,<B> --quiet</B>
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<DD>
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Suppress "not mounted" error messages.
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<DT id="13"><B>-R</B>,<B> --recursive</B>
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<DD>
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Recursively unmount each specified directory. Recursion for each directory will
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stop if any unmount operation in the chain fails for any reason. The relationship
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between mountpoints is determined by /proc/self/mountinfo entries. The filesystem
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must be specified by mountpoint path; a recursive unmount by device name (or UUID)
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is unsupported.
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<DT id="14"><B>-r</B>,<B> --read-only</B>
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<DD>
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When an unmount fails, try to remount the filesystem read-only.
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<DT id="15"><B>-t</B>,<B> --types </B><I>type</I>...
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<DD>
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Indicate that the actions should only be taken on filesystems of the
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specified
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<I>type</I>.
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More than one type may be specified in a comma-separated list. The list
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of filesystem types can be prefixed with
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<B>no</B>
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to indicate that no action should be taken for all of the mentioned types.
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Note that
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<B>umount</B>
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reads information about mounted filesystems from kernel (/proc/mounts) and
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filesystem names may be different than filesystem names used in the /etc/fstab
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(e.g. "nfs4" vs. "nfs").
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<DT id="16"><B>-v</B>,<B> --verbose</B>
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<DD>
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Verbose mode.
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<DT id="17"><B>-V</B>,<B> --version</B>
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<DD>
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Display version information and exit.
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<DT id="18"><B>-h</B>,<B> --help</B>
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<DD>
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Display help text and exit.
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</DL>
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<A NAME="lbAF"> </A>
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<H2>LOOP DEVICE</H2>
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The
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<B>umount</B>
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command will automatically detach loop device previously initialized by
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<B><A HREF="/cgi-bin/man/man2html?8+mount">mount</A></B>(8)
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command independently of /etc/mtab.
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<P>
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In this case the device is initialized with "autoclear" flag (see
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<B><A HREF="/cgi-bin/man/man2html?8+losetup">losetup</A></B>(8)
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output for more details), otherwise it's necessary to use the option <B> --detach-loop</B>
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or call <B>losetup -d <device></B>. The autoclear feature is supported since Linux 2.6.25.
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<A NAME="lbAG"> </A>
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<H2>EXTERNAL HELPERS</H2>
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The syntax of external unmount helpers is:
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<P>
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<DL COMPACT><DT id="19"><DD>
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<B>umount.</B><I>suffix</I>
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{<I>directory</I>|<I>device</I>}
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[<B>-flnrv</B>]
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[<B>-N</B>
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<I>namespace</I>]
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[<B>-t</B>
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<I>type</I>.<I>subtype</I>]
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</DL>
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<P>
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where <I>suffix</I> is the filesystem type (or the value from a
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<B>uhelper=</B> or <B>helper=</B> marker in the mtab file).
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The <B>-t</B> option can be used for filesystems that
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have subtype support. For example:
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<P>
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<DL COMPACT><DT id="20"><DD>
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<B>umount.fuse -t fuse.sshfs</B>
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</DL>
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<P>
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A <B>uhelper=</B><I>something</I> marker (unprivileged helper) can appear in
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the <I>/etc/mtab</I> file when ordinary users need to be able to unmount
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a mountpoint that is not defined in <I>/etc/fstab</I>
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(for example for a device that was mounted by <B><A HREF="/cgi-bin/man/man2html?1+udisks">udisks</A></B>(1)).
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<P>
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A <B>helper=</B><I>type</I> marker in the mtab file will redirect
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all unmount requests
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to the <B>/sbin/umount.</B><I>type</I> helper independently of UID.
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<P>
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Note that <I>/etc/mtab</I> is currently deprecated and helper= and another
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userspace mount options are maintained by libmount.
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<A NAME="lbAH"> </A>
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<H2>FILES</H2>
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<DL COMPACT>
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<DT id="21"><I>/etc/mtab</I>
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<DD>
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table of mounted filesystems (deprecated and usually replaced by
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symlink to /proc/mounts)
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<DT id="22"><I>/etc/fstab</I>
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<DD>
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table of known filesystems
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<DT id="23"><I>/proc/self/mountinfo</I>
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<DD>
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table of mounted filesystems generated by kernel.
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</DL>
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<A NAME="lbAI"> </A>
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<H2>ENVIRONMENT</H2>
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<DL COMPACT>
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<DT id="24">LIBMOUNT_FSTAB=<path><DD>
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overrides the default location of the fstab file (ignored for suid)
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<DT id="25">LIBMOUNT_MTAB=<path><DD>
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overrides the default location of the mtab file (ignored for suid)
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<DT id="26">LIBMOUNT_DEBUG=all<DD>
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enables libmount debug output
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</DL>
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<A NAME="lbAJ"> </A>
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<H2>SEE ALSO</H2>
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<B><A HREF="/cgi-bin/man/man2html?2+umount">umount</A></B>(2),
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<B><A HREF="/cgi-bin/man/man2html?8+losetup">losetup</A></B>(8),
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<B><A HREF="/cgi-bin/man/man2html?8+mount">mount</A></B>(8)
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<A NAME="lbAK"> </A>
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<H2>HISTORY</H2>
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A
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<B>umount</B>
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command appeared in Version 6 AT&T UNIX.
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<A NAME="lbAL"> </A>
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<H2>AVAILABILITY</H2>
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The umount command is part of the util-linux package and is available from
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Linux Kernel Archive
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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="27"><A HREF="#lbAB">NAME</A><DD>
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<DT id="28"><A HREF="#lbAC">SYNOPSIS</A><DD>
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<DT id="29"><A HREF="#lbAD">DESCRIPTION</A><DD>
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<DT id="30"><A HREF="#lbAE">OPTIONS</A><DD>
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<DT id="31"><A HREF="#lbAF">LOOP DEVICE</A><DD>
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<DT id="32"><A HREF="#lbAG">EXTERNAL HELPERS</A><DD>
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<DT id="33"><A HREF="#lbAH">FILES</A><DD>
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<DT id="34"><A HREF="#lbAI">ENVIRONMENT</A><DD>
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<DT id="35"><A HREF="#lbAJ">SEE ALSO</A><DD>
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<DT id="36"><A HREF="#lbAK">HISTORY</A><DD>
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<DT id="37"><A HREF="#lbAL">AVAILABILITY</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: 00:06:18 GMT, March 31, 2021
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</BODY>
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</HTML>
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