.\" Copyright (C) 1993 Rickard E. Faith .\" and Copyright (C) 1994 Andries E. Brouwer .\" and Copyright (C) 2002, 2005 Michael Kerrisk .\" .\" %%%LICENSE_START(VERBATIM) .\" Permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" Permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" Since the Linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. The author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. The author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" Formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%LICENSE_END .\" .\" 2008-10-06, mtk: Created this as a new page by splitting .\" umount/umount2 material out of mount.2 .\" .TH UMOUNT 2 2016-07-17 "Linux" "Linux Programmer's Manual" .SH NAME umount, umount2 \- unmount filesystem .SH SYNOPSIS .nf .B "#include " .sp .BI "int umount(const char *" target ); .sp .BI "int umount2(const char *" target ", int " flags ); .fi .SH DESCRIPTION .BR umount () and .BR umount2 () remove the attachment of the (topmost) filesystem mounted on .IR target . .\" Note: the kernel naming differs from the glibc naming .\" umount2 is the glibc name for what the kernel now calls umount .\" and umount is the glibc name for oldumount Appropriate privilege (Linux: the .B CAP_SYS_ADMIN capability) is required to unmount filesystems. Linux 2.1.116 added the .BR umount2 () system call, which, like .BR umount (), unmounts a target, but allows additional .I flags controlling the behavior of the operation: .TP .BR MNT_FORCE " (since Linux 2.1.116)" Force unmount even if busy. This can cause data loss. (Only for NFS mounts.) .TP .BR MNT_DETACH " (since Linux 2.4.11)" Perform a lazy unmount: make the mount point unavailable for new accesses, immediately disconnect the filesystem and all filesystems mounted below it from each other and from the mount table, and actually perform the unmount when the mount point ceases to be busy. .TP .BR 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 .BR umount2 () with this flag fails with the error .BR 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 .BR umount2 () call specifying .B MNT_EXPIRE unmounts an expired mount point. This flag cannot be specified with either .B MNT_FORCE or .BR MNT_DETACH . .TP .BR UMOUNT_NOFOLLOW " (since Linux 2.6.34)" .\" Later added to 2.6.33-stable Don't dereference .I target if it is a symbolic link. This flag allows security problems to be avoided in set-user-ID-\fIroot\fP programs that allow unprivileged users to unmount filesystems. .SH RETURN VALUE On success, zero is returned. On error, \-1 is returned, and .I errno is set appropriately. .SH ERRORS The error values given below result from filesystem type independent errors. Each filesystem type may have its own special errors and its own special behavior. See the Linux kernel source code for details. .TP .B EAGAIN A call to .BR umount2 () specifying .B MNT_EXPIRE successfully marked an unbusy filesystem as expired. .TP .B EBUSY .I target could not be unmounted because it is busy. .TP .B EFAULT .I target points outside the user address space. .TP .B EINVAL .I target is not a mount point. .TP .B EINVAL .BR umount2 () was called with .B MNT_EXPIRE and either .B MNT_DETACH or .BR MNT_FORCE . .TP .BR EINVAL " (since Linux 2.6.34)" .BR umount2 () was called with an invalid flag value in .IR flags . .TP .B ENAMETOOLONG A pathname was longer than .BR MAXPATHLEN . .TP .B ENOENT A pathname was empty or had a nonexistent component. .TP .B ENOMEM The kernel could not allocate a free page to copy filenames or data into. .TP .B EPERM The caller does not have the required privileges. .SH VERSIONS .BR MNT_DETACH and .BR MNT_EXPIRE .\" http://sourceware.org/bugzilla/show_bug.cgi?id=10092 are available in glibc since version 2.11. .SH CONFORMING TO These functions are Linux-specific and should not be used in programs intended to be portable. .SH NOTES .SS umount() and shared mount points Shared mount points cause any mount activity on a mount point, including .BR umount () operations, to be forwarded to every shared mount point in the peer group and every slave mount of that peer group. This means that .BR umount () of any peer in a set of shared mounts will cause all of its peers to be unmounted and all of their slaves to be unmounted as well. This propagation of unmount activity can be particularly surprising on systems where every mount point is shared by default. On such systems, recursively bind mounting the root directory of the filesystem onto a subdirectory and then later unmounting that subdirectory with .BR MNT_DETACH will cause every mount in the mount namespace to be lazily unmounted. To ensure .BR umount () does not propagate in this fashion, the mount point may be remounted using a .BR mount () call with a .I mount_flags argument that includes both .BR MS_REC and .BR MS_PRIVATE prior to .BR umount () being called. .SS Historical details The original .BR umount () function was called as \fIumount(device)\fP and would return .B ENOTBLK when called with something other than a block device. In Linux 0.98p4, a call \fIumount(dir)\fP was added, in order to support anonymous devices. In Linux 2.3.99-pre7, the call \fIumount(device)\fP was removed, leaving only \fIumount(dir)\fP (since now devices can be mounted in more than one place, so specifying the device does not suffice). .SH SEE ALSO .BR mount (2), .BR mount_namespaces (7), .BR path_resolution (7), .BR mount (8), .BR umount (8) .SH COLOPHON This page is part of release 4.10 of the Linux .I man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/.