1UMOUNT(2) Linux Programmer's Manual UMOUNT(2)
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6 umount, umount2 - unmount filesystem
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9 #include <sys/mount.h>
10 int umount(const char *target);
12 int umount2(const char *target, int flags);
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16 umount() and umount2() remove the attachment of the (topmost) filesys‐
17 tem mounted on target.
18 Appropriate privilege (Linux: the CAP_SYS_ADMIN capability) is required
20 to unmount filesystems.
21 Linux 2.1.116 added the umount2() system call, which, like umount(),
23 unmounts a target, but allows additional flags controlling the behavior
24 of the operation:
25 MNT_FORCE (since Linux 2.1.116)
27 Ask the filesystem to abort pending requests before attempting
28 the unmount. This may allow the unmount to complete without
29 waiting for an inaccessible server, but could cause data loss.
30 If, after aborting requests, some processes still have active
31 references to the filesystem, the unmount will still fail. As
32 at Linux 4.12, MNT_FORCE is supported only on the following
33 filesystems: 9p (since Linux 2.6.16), ceph (since Linux 2.6.34),
34 cifs (since Linux 2.6.12), fuse (since Linux 2.6.16), lustre
35 (since Linux 3.11), and NFS (since Linux 2.1.116).
36 MNT_DETACH (since Linux 2.4.11)
38 Perform a lazy unmount: make the mount point unavailable for new
39 accesses, immediately disconnect the filesystem and all filesys‐
40 tems mounted below it from each other and from the mount table,
41 and actually perform the unmount when the mount point ceases to
42 be busy.
43 MNT_EXPIRE (since Linux 2.6.8)
45 Mark the mount point as expired. If a mount point is not cur‐
46 rently in use, then an initial call to umount2() with this flag
47 fails with the error EAGAIN, but marks the mount point as ex‐
48 pired. The mount point remains expired as long as it isn't ac‐
49 cessed by any process. A second umount2() call specifying
50 MNT_EXPIRE unmounts an expired mount point. This flag cannot be
51 specified with either MNT_FORCE or MNT_DETACH.
52 UMOUNT_NOFOLLOW (since Linux 2.6.34)
54 Don't dereference target if it is a symbolic link. This flag
55 allows security problems to be avoided in set-user-ID-root pro‐
56 grams that allow unprivileged users to unmount filesystems.
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59 On success, zero is returned. On error, -1 is returned, and errno is
60 set appropriately.
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63 The error values given below result from filesystem type independent
64 errors. Each filesystem type may have its own special errors and its
65 own special behavior. See the Linux kernel source code for details.
66 EAGAIN A call to umount2() specifying MNT_EXPIRE successfully marked an
68 unbusy filesystem as expired.
69 EBUSY target could not be unmounted because it is busy.
71 EFAULT target point