.\" Hey Emacs! This file is -*- nroff -*- source. .\" .\" Copyright (C) 1993 Rickard E. Faith .\" Copyright (C) 1994 Andries E. Brouwer .\" Copyright (C) 2002 Michael Kerrisk .\" .\" 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 .\" .\" Since the Linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date.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. .\" .\" Modified 1996-11-04 by Eric S. Raymond .\" Modified 2001-10-13 by Michael Kerrisk .\" Added note on historical behaviour of MS_NOSUID .\" Modified 2002-05-16 by Michael Kerrisk .\" Extensive changes and additions .\" Modified 2002-05-27 by aeb .\" Modified 2002-06-11 by Michael Kerrisk .\" Enhanced descriptions of MS_MOVE, MS_BIND, and MS_REMOUNT .\" Modified 2004-06-17 by Michael Kerrisk .\" .TH MOUNT 2 2004-06-17 "Linux 2.6" "Linux Programmer's Manual" .SH NAME mount, umount \- mount and unmount filesystems .SH SYNOPSIS .B "#include " .sp .BI "int mount(const char *" source ", const char *" target , .BI "const char *" filesystemtype ", unsigned long " mountflags , .BI "const void *" data ); .sp .BI "int umount(const char *" target ); .sp .BI "int umount2(const char *" target ", int " flags ); .SH DESCRIPTION .B mount attaches the filesystem specified by .I source (which is often a device name, but can also be a directory name or a dummy) to the directory specified by .IR target . .BR umount " and " umount2 remove the attachment of the (topmost) filesystem mounted on .IR target . Appropriate privilege (Linux: the .B CAP_SYS_ADMIN capability) is required to 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. .\" Multiple mounts on same mount point: since 2.3.99pre7. Values for the .IR filesystemtype argument supported by the kernel are listed in .I /proc/filesystems (like "minix", "ext2", "msdos", "proc", "nfs", "iso9660" etc.). Further types may become available when the appropriate modules are loaded. The .IR mountflags argument may have the magic number 0xC0ED (\fBMS_MGC_VAL\fP) 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 for libc4 and libc5 and in for glibc2) in the low order 16 bits: .TP .B MS_BIND (Linux 2.4 onwards) .\" since 2.4.0-test9 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 .BR chroot (2) jails. The .IR filesystemtype ", " mountflags ", and " data arguments are ignored. .\" with the exception of the "hidden" MS_REC mountflags bit .TP .B 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 .BR chattr (8).) .TP .B 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 .BR fcntl (2).) .\" FIXME: More can be said about MS_MOVE .TP .B MS_MOVE Move a subtree. .I source specifies an existing mount point and .I target specifies the new location. The move is atomic: at no point is the subtree unmounted. The .IR filesystemtype ", " mountflags ", and " data arguments are ignored. .TP .B MS_NOATIME Do not update access times for (all types of) files on this file system. .TP .B MS_NODEV Do not allow access to devices (special files) on this file system. .TP .B MS_NODIRATIME Do not update access times for directories on this file system. .TP .B MS_NOEXEC Do not allow programs to be executed from this file system. .\" (Possibly useful for a file system that contains non-Linux executables. .\" Often used as a security feature, e.g. to make sure that restricted .\" users cannot execute files uploaded using ftp or so.) .TP .B MS_NOSUID Do not honour set-UID and set-GID bits when executing programs from this file system. .\" (This is a security feature to prevent users executing set-UID and .\" set-GID programs from removable disk devices.) .TP .B MS_RDONLY Mount file system read-only. .TP .B MS_REMOUNT Remount an existing mount. This is allows you to change the .I mountflags and .I data of an existing mount without having to unmount and remount the file system. .I source and .I target should be the same values specified in the initial .BR mount () call; .I filesystemtype is ignored. .TP .B MS_SYNCHRONOUS Make writes on this file system synchronous (as though the .B O_SYNC flag to .BR open (2) was specified for all file opens to this file system). .PP From Linux 2.4 onwards, the .BR MS_NODEV ", " MS_NOEXEC ", and " MS_NOSUID flags are settable on a per-mount point basis. .PP The .IR data argument is interpreted by the different file systems. Typically it is a string of comma-separated options understood by this file system. See .BR mount (8) for details of the options available for each filesystem type. .PP .\" 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 Linux 2.1.116 added the .BR umount2 () system call, which, like .BR umount (), unmounts a target, but allows additional .I flags controlling the behaviour of the operation: .TP .B MNT_FORCE Force unmount even if busy. (Since 2.1.116. Only for NFS mounts.) .TP .B 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.) .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 kernel source code for details. .TP .B EACCES A component of a path was not searchable. (See also .BR path_resolution (2).) .br Or, mounting a read-only filesystem was attempted without giving the MS_RDONLY flag. .br Or, the block device .I source is located on a filesystem mounted with the MS_NODEV option. .\" mtk: Probably: write permission is required for MS_BIND, with .\" the error EPERM if not present; CAP_DAC_OVERRIDE is required. .TP .B EBUSY .I 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 .I target because .I 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. .TP .B EFAULT One of the pointer arguments points outside the user address space. .TP .B EINVAL .I source had an invalid superblock. Or, a remount was attempted, while .I source was not already mounted on .IR target . Or, a move was attempted, while .I source was not a mount point, or was '/'. Or, an umount was attempted, while .I target was not a mount point. .TP .B ELOOP Too many link encountered during pathname resolution. Or, a move was attempted, while .I target is a descendant of .IR source . .TP .B EMFILE (In case no block device is required:) Table of dummy devices is full. .TP .B ENAMETOOLONG A pathname was longer than MAXPATHLEN. .TP .B ENODEV .I Filesystemtype not configured in the kernel. .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 ENOTBLK .I source is not a block device (and a device was required). .TP .B ENOTDIR The second argument, or a prefix of the first argument, is not a directory. .TP .B ENXIO The major number of the block device .I source is out of range. .TP .B EPERM The caller does not have the required privileges. .SH "CONFORMING TO" These functions are Linux-specific and should not be used in programs intended to be portable. .SH HISTORY The original .B umount function was called as \fIumount(device)\fP and would return 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). .LP The original MS_SYNC flag was renamed MS_SYNCHRONOUS in 1.1.69 when a different MS_SYNC was added to . .LP Before Linux 2.4 an attempt to execute a set-UID or set-GID program on a filesystem mounted with .B MS_NOSUID would fail with .BR EPERM . Since Linux 2.4 the set-UID and set-GID bits are just silently ignored in this case. .\" The change is in patch-2.4.0-prerelease. .SH "SEE ALSO" .BR path_resolution (2), .BR mount (8), .BR umount (8)