1 .\" Copyright (C) 1993 Rickard E. Faith <faith@cs.unc.edu>
2 .\" and Copyright (C) 1994 Andries E. Brouwer <aeb@cwi.nl>
3 .\" and Copyright (C) 2002, 2005 Michael Kerrisk <mtk.manpages@gmail.com>
5 .\" %%%LICENSE_START(VERBATIM)
6 .\" Permission is granted to make and distribute verbatim copies of this
7 .\" manual provided the copyright notice and this permission notice are
8 .\" preserved on all copies.
10 .\" Permission is granted to copy and distribute modified versions of this
11 .\" manual under the conditions for verbatim copying, provided that the
12 .\" entire resulting derived work is distributed under the terms of a
13 .\" permission notice identical to this one.
15 .\" Since the Linux kernel and libraries are constantly changing, this
16 .\" manual page may be incorrect or out-of-date. The author(s) assume no
17 .\" responsibility for errors or omissions, or for damages resulting from
18 .\" the use of the information contained herein. The author(s) may not
19 .\" have taken the same level of care in the production of this manual,
20 .\" which is licensed free of charge, as they might when working
23 .\" Formatted or processed versions of this manual, if unaccompanied by
24 .\" the source, must acknowledge the copyright and authors of this work.
27 .\" 2008-10-06, mtk: Created this as a new page by splitting
28 .\" umount/umount2 material out of mount.2
30 .TH UMOUNT 2 2021-08-27 "Linux" "Linux Programmer's Manual"
32 umount, umount2 \- unmount filesystem
35 .B "#include <sys/mount.h>"
37 .BI "int umount(const char *" target );
38 .BI "int umount2(const char *" target ", int " flags );
44 remove the attachment of the (topmost) filesystem mounted on
46 .\" Note: the kernel naming differs from the glibc naming
47 .\" umount2 is the glibc name for what the kernel now calls umount
48 .\" and umount is the glibc name for oldumount
50 Appropriate privilege (Linux: the
52 capability) is required to unmount filesystems.
54 Linux 2.1.116 added the
56 system call, which, like
58 unmounts a target, but allows additional
60 controlling the behavior of the operation:
62 .BR MNT_FORCE " (since Linux 2.1.116)"
63 Ask the filesystem to abort pending requests before attempting the
65 This may allow the unmount to complete without waiting
66 for an inaccessible server, but could cause data loss.
67 If, after aborting requests,
68 some processes still have active references to the filesystem,
69 the unmount will still fail.
72 is supported only on the following filesystems:
73 9p (since Linux 2.6.16),
74 ceph (since Linux 2.6.34),
75 cifs (since Linux 2.6.12),
76 fuse (since Linux 2.6.16),
77 lustre (since Linux 3.11),
78 and NFS (since Linux 2.1.116).
80 .BR MNT_DETACH " (since Linux 2.4.11)"
81 Perform a lazy unmount: make the mount unavailable for new
82 accesses, immediately disconnect the filesystem and all filesystems
83 mounted below it from each other and from the mount table, and
84 actually perform the unmount when the mount ceases to be busy.
86 .BR MNT_EXPIRE " (since Linux 2.6.8)"
87 Mark the mount as expired.
88 If a mount is not currently in use, then an initial call to
90 with this flag fails with the error
92 but marks the mount as expired.
93 The mount remains expired as long as it isn't accessed
99 unmounts an expired mount.
100 This flag cannot be specified with either
105 .BR UMOUNT_NOFOLLOW " (since Linux 2.6.34)"
106 .\" Later added to 2.6.33-stable
109 if it is a symbolic link.
110 This flag allows security problems to be avoided in set-user-ID-\fIroot\fP
111 programs that allow unprivileged users to unmount filesystems.
113 On success, zero is returned.
114 On error, \-1 is returned, and
116 is set to indicate the error.
118 The error values given below result from filesystem type independent
120 Each filesystem type may have its own special errors and its
121 own special behavior.
122 See the Linux kernel source code for details.
129 successfully marked an unbusy filesystem as expired.
133 could not be unmounted because it is busy.
137 points outside the user address space.
141 is not a mount point.
146 .BR mount_namespaces (7).
157 .BR EINVAL " (since Linux 2.6.34)"
159 was called with an invalid flag value in
163 A pathname was longer than
167 A pathname was empty or had a nonexistent component.
170 The kernel could not allocate a free page to copy filenames or data into.
173 The caller does not have the required privileges.
178 .\" http://sourceware.org/bugzilla/show_bug.cgi?id=10092
179 are available in glibc since version 2.11.
181 These functions are Linux-specific and should not be used in
182 programs intended to be portable.
184 .SS umount() and shared mounts
185 Shared mounts cause any mount activity on a mount, including
187 operations, to be forwarded to every shared mount in the
188 peer group and every slave mount of that peer group.
191 of any peer in a set of shared mounts will cause all of its
192 peers to be unmounted and all of their slaves to be unmounted as well.
194 This propagation of unmount activity can be particularly surprising
195 on systems where every mount is shared by default.
197 recursively bind mounting the root directory of the filesystem
198 onto a subdirectory and then later unmounting that subdirectory with
200 will cause every mount in the mount namespace to be lazily unmounted.
204 does not propagate in this fashion,
205 the mount may be remounted using a
209 argument that includes both
216 .SS Historical details
219 function was called as \fIumount(device)\fP and would return
221 when called with something other than a block device.
222 In Linux 0.98p4, a call \fIumount(dir)\fP was added, in order to
223 support anonymous devices.
224 In Linux 2.3.99-pre7, the call \fIumount(device)\fP was removed,
225 leaving only \fIumount(dir)\fP (since now devices can be mounted
226 in more than one place, so specifying the device does not suffice).
229 .BR mount_namespaces (7),
230 .BR path_resolution (7),