| .\" Copyright (C) 1993 Rickard E. Faith <faith@cs.unc.edu> |
| .\" and Copyright (C) 1994 Andries E. Brouwer <aeb@cwi.nl> |
| .\" and Copyright (C) 2002, 2005 Michael Kerrisk <mtk.manpages@gmail.com> |
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| .\" 2008-10-06, mtk: Created this as a new page by splitting |
| .\" umount/umount2 material out of mount.2 |
| .\" |
| .TH UMOUNT 2 2017-09-15 "Linux" "Linux Programmer's Manual" |
| .SH NAME |
| umount, umount2 \- unmount filesystem |
| .SH SYNOPSIS |
| .nf |
| .B "#include <sys/mount.h>" |
| .PP |
| .BI "int umount(const char *" target ); |
| .PP |
| .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 |
| .PP |
| Appropriate privilege (Linux: the |
| .B CAP_SYS_ADMIN |
| capability) is required to unmount filesystems. |
| .PP |
| 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)" |
| Ask the filesystem to abort pending requests before attempting the |
| unmount. |
| This may allow the unmount to complete without waiting |
| for an inaccessible server, but could cause data loss. |
| If, after aborting requests, |
| some processes still have active references to the filesystem, |
| the unmount will still fail. |
| As at Linux 4.12, |
| .BR MNT_FORCE |
| is supported only on the following filesystems: |
| 9p (since Linux 2.6.16), |
| ceph (since Linux 2.6.34), |
| cifs (since Linux 2.6.12), |
| fuse (since Linux 2.6.16), |
| lustre (since Linux 3.11), |
| and NFS (since Linux 2.1.116). |
| .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. |
| .PP |
| 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. |
| .PP |
| 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) |
