功能說明：卸除文件系統。

語法：umount[-ahnrvV][-t<文件系統類型>][文件系統]

補充說明：umount可卸除目前掛在Linux目錄中的文件系統。

參數：

-a卸除/etc/mtab中記錄的所有文件系統。

-h顯示幫助。

-n卸除時不要將信息存入/etc/mtab文件中。

-r若無法成功卸除，則嘗試以只讀的方式重新掛入文件系統。

-t<文件系統類型>僅卸除選項中所指定的文件系統。

-v執行時顯示詳細的信息。

-V顯示版本信息。

[文件系統]除了直接指定文件系統外，也可以用設備名稱或掛入點來表示文件系統。

#p#

NAME

mount, umount - mount and unmount filesystems  

SYNOPSIS

#include <sys/mount.h>

int mount(const char *source, const char *target, const char *filesystemtype, unsigned long mountflags, const void *data);

int umount(const char *target);

int umount2(const char *target, int flags);  

DESCRIPTION

mount attaches the filesystem specified by source (which is often a device name, but can also be a directory name or a dummy) to the directory specified by target.

umount and umount2 remove the attachment of the (topmost) filesystem mounted on target.

Only the super-user may mount and unmount filesystems. Since Linux 2.4 a single filesystem can be visible at multiple mount points, and multiple mounts can be stacked on the same mount point.

Values for the filesystemtype argument supported by the kernel are listed in /proc/filesystems (like "minix", "ext2", "msdos", "proc", "nfs", "iso9660" etc.). Further types may become available when the appropriate modules are loaded.

The mountflags argument may have the magic number 0xC0ED (MS_MGC_VAL) in the top 16 bits (this was required in kernel versions prior to 2.4, but is no longer required and ignored if specified), and various mount flags (as defined in <linux/fs.h> for libc4 and libc5 and in <sys/mount.h> for glibc2) in the low order 16 bits:

MS_BIND

(Linux 2.4 onwards) Perform a bind mount, making a file or a directory subtree visible at another point within a file system. Bind mounts may cross file system boundaries and span chroot(2) jails. The filesystemtype, mountflags, and data arguments are ignored.

MS_DIRSYNC

(Since Linux 2.5.19.) Make directory changes on this file system synchronous. (This property can be obtained for individual directories or subtrees using chattr(8).)

MS_MANDLOCK

Permit mandatory locking on files in this file system. (Mandatory locking must still be enabled on a per-file basis, as described in fcntl(2).)

MS_MOVE

Move a subtree. source specifies an existing mount point and target specifies the new location. The move is atomic: at no point is the subtree unmounted. The filesystemtype, mountflags, and data arguments are ignored.

MS_NOATIME

Do not update access times for (all types of) files on this file system.

MS_NODEV

Do not allow access to devices (special files) on this file system.

MS_NODIRATIME

Do not update access times for directories on this file system.

MS_NOEXEC

Do not allow programs to be executed from this file system.

MS_NOSUID

Do not honour set-UID and set-GID bits when executing programs from this file system.

MS_RDONLY

Mount file system read-only.

MS_REMOUNT

Remount an existing mount. This is allows you to change the mountflags and data of an existing mount without having to unmount and remount the file system. source and target should be the same values specified in the initial mount() call; filesystemtype is ignored.

MS_SYNCHRONOUS

Make writes on this file system synchronous (as though the O_SYNC flag to open(2) was specified for all file opens to this file system).

From Linux 2.4 onwards, the MS_NODEV, MS_NOEXEC, and MS_NOSUID flags are settable on a per-mount point basis.

The data argument is interpreted by the different file systems. Typically it is a string of comma-separated options understood by this file system. See mount(8) for details of the options available for each filesystem type.

Linux 2.1.116 added the umount2() system call, which, like umount(), unmounts a target, but allows additional flags controlling the behaviour of the operation:

MNT_FORCE

Force unmount even if busy. (Since 2.1.116. Only for NFS mounts.)

MNT_DETACH

Perform a lazy unmount: make the mount point unavailable for new accesses, and actually perform the unmount when the mount point ceases to be busy. (Since 2.4.11.)

RETURN VALUE

On success, zero is returned. On error, -1 is returned, and errno is set appropriately.  

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 kernel source code for details.

EPERM

The user is not the super-user.

ENODEV

Filesystemtype not configured in the kernel.

ENOTBLK

Source is not a block device (and a device was required).

EBUSY

Source is already mounted. Or, it cannot be remounted read-only, because it still holds files open for writing. Or, it cannot be mounted on target because target is still busy (it is the working directory of some task, the mount point of another device, has open files, etc.). Or, it could not be unmounted because it is busy.

EINVAL

Source had an invalid superblock. Or, a remount was attempted, while source was not already mounted on target. Or, a move was attempted, while source was not a mount point, or was '/'. Or, an umount was attempted, while target was not a mount point.

ENOTDIR

The second argument, or a prefix of the first argument, is not a directory.

EFAULT

One of the pointer arguments points outside the user address space.

ENOMEM

The kernel could not allocate a free page to copy filenames or data into.

ENAMETOOLONG

A pathname was longer than MAXPATHLEN.

ENOENT

A pathname was empty or had a nonexistent component.

ELOOP

Too many link encountered during pathname resolution. Or, a move was attempted, while target is a descendant of source.

EACCES

A component of a path was not searchable.
Or, mounting a read-only filesystem was attempted without giving the MS_RDONLY flag.
Or, the block device Source is located on a filesystem mounted with the MS_NODEV option.

ENXIO

The major number of the block device source is out of range.

EMFILE

(In case no block device is required:) Table of dummy devices is full.

CONFORMING TO

These functions are Linux-specific and should not be used in programs intended to be portable.  

HISTORY

The original umount function was called as umount(device) and would return ENOTBLK when called with something other than a block device. In Linux 0.98p4 a call umount(dir) was added, in order to support anonymous devices. In Linux 2.3.99-pre7 the call umount(device) was removed, leaving only umount(dir) (since now devices can be mounted in more than one place, so specifying the device does not suffice).

The original MS_SYNC flag was renamed MS_SYNCHRONOUS in 1.1.69 when a different MS_SYNC was added to <mman.h>.

Before Linux 2.4 an attempt to execute a set-UID or set-GID program on a filesystem mounted with MS_NOSUID would fail with EPERM. Since Linux 2.4 the set-UID and set-GID bits are just silently ignored in this case.  

SEE ALSO

mount(8), umount(8)