.\" Hey Emacs! This file is -*- nroff -*- source. .\" .\" Copyright (C) 1993 Rickard E. Faith .\" and Copyright (C) 1994 Andries E. Brouwer .\" and Copyright (C) 2002, 2005 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 .\" .\" Since the Linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date.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 behavior 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 .\" 2005-05-18, mtk, Added MNT_EXPIRE, plus a few other tidy-ups. .\" 2008-10-06, mtk: move umount*() material into separate umount.2 page. .\" 2008-10-06, mtk: Add discussion of namespaces. .\" .TH MOUNT 2 2012-07-05 "Linux" "Linux Programmer's Manual" .SH NAME mount \- mount file system .SH SYNOPSIS .nf .B "#include " .sp .BI "int mount(const char *" source ", const char *" target , .BI " const char *" filesystemtype ", unsigned long " mountflags , .BI " const void *" data ); .fi .SH DESCRIPTION .BR mount () attaches the file system 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 . Appropriate privilege (Linux: the .B CAP_SYS_ADMIN capability) is required to mount file systems. Since Linux 2.4 a single file system 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 .I filesystemtype argument supported by the kernel are listed in .I /proc/filesystems (e.g., "minix", "ext2", "ext3", "jfs", "xfs", "reiserfs", "msdos", "proc", "nfs", "iso9660"). Further types may become available when the appropriate modules are loaded. The .I 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 \fI\fP for libc4 and libc5 .\" and in \fI\fP for glibc2) in the low order 16 bits: .\" FIXME 2.6.15 added flags for "shared subtree" functionality: .\" MS_UNBINDABLE, MS_PRIVATE, MS_SHARED, MS_SLAVE .\" These need to be documented on this page. .\" See: .\" Documentation/filesystems/sharedsubtree.txt .\" .\" http://lwn.net/Articles/159077/ .\" .\" http://myweb.sudhaa.com:2022/~ram/sharedsubtree/paper/sharedsubtree.1.pdf .\" Shared-Subtree Concept, Implementation, and Applications in Linux .\" Al Viro viro@ftp.linux.org.uk .\" Ram Pai linuxram@us.ibm.com .\" .\" http://foss.in/2005/slides/sharedsubtree1.pdf .\" Shared Subtree Concept and Implementation in the Linux Kernel .\" Ram Pai .\" .\" 2.6.25 Added MS_I_VERSION, which needs to be documented. .\" .TP .BR MS_BIND " (Linux 2.4 onward)" .\" 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 and .IR data arguments are ignored. Up until Linux 2.6.26, .I mountflags was also ignored .\" with the exception of the "hidden" MS_REC mountflags bit (the bind mount has the same mount options as the underlying mount point). .TP .BR 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 (1).) .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 Say more 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. This flag provides a subset of the functionality provided by .BR MS_NOATIME ; that is, .BR MS_NOATIME implies .BR MS_NODIRATIME . .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 honor set-user-ID and set-group-ID bits when executing programs from this file system. .\" (This is a security feature to prevent users executing set-user-ID and .\" set-group-ID programs from removable disk devices.) .TP .B MS_RDONLY Mount file system read-only. .\" .\" FIXME Document MS_REC, available since 2.4.11. .\" This flag has meaning in conjunction with MS_BIND and .\" also with the shared subtree flags. .TP .BR MS_RELATIME " (Since Linux 2.6.20)" When a file on this file system is accessed, only update the file's last access time (atime) if the current value of atime is less than or equal to the file's last modification time (mtime) or last status change time (ctime). This option is useful for programs, such as .BR mutt (1), that need to know when a file has been read since it was last modified. Since Linux 2.6.30, the kernel defaults to the behavior provided by this flag (unless .BR MS_NOATIME was specified), and the .B MS_STRICTATIME flag is required to obtain traditional semantics. In addition, since Linux 2.6.30, the file's last access time is always updated if it is more than 1 day old. .\" Matthew Garrett notes in the patch that added this behavior .\" that this lets utilities such as tmpreaper (which deletes .\" files based on last acces time) work correctly. .TP .B MS_REMOUNT Remount an existing mount. This allows you to change the .I mountflags and .I data of an existing mount without having to unmount and remount the file system. .I target should be the same value specified in the initial .BR mount () call; .I source and .I filesystemtype are ignored. The following .I mountflags can be changed: .BR MS_RDONLY , .BR MS_SYNCHRONOUS , .BR MS_MANDLOCK ; before kernel 2.6.16, the following could also be changed: .B MS_NOATIME and .BR MS_NODIRATIME ; and, additionally, before kernel 2.4.10, the following could also be changed: .BR MS_NOSUID , .BR MS_NODEV , .BR MS_NOEXEC . .TP .BR MS_SILENT " (since Linux 2.6.17)" Suppress the display of certain .RI ( printk ()) warning messages in the kernel log. This flag supersedes the misnamed and obsolete .BR MS_VERBOSE flag (available since Linux 2.4.12), which has the same meaning. .TP .BR MS_STRICTATIME " (Since Linux 2.6.30)" Always update the last access time (atime) when files on this file system are accessed. (This was the default behavior before Linux 2.6.30.) Specifying this flag overrides the effect of setting the .BR MS_NOATIME and .BR MS_RELATIME flags. .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 onward, the .BR MS_NODEV ", " MS_NOEXEC ", and " MS_NOSUID flags are settable on a per-mount-point basis. From kernel 2.6.16 onward, .B MS_NOATIME and .B MS_NODIRATIME are also settable on a per-mount-point basis. The .B MS_RELATIME flag is also settable on a per-mount-point basis. .PP The .I 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. .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 file-system type may have its own special errors and its own special behavior. See the Linux kernel source code for details. .TP .B EACCES A component of a path was not searchable. (See also .BR path_resolution (7).) Or, mounting a read-only file system was attempted without giving the .B MS_RDONLY flag. Or, the block device .I source is located on a file system mounted with the .B 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 thread, the mount point of another device, has open files, etc.). .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 .RB ( MS_REMOUNT ) was attempted, but .I source was not already mounted on .IR target . Or, a move .RB ( MS_MOVE ) was attempted, but .I source was not a mount point, or was \(aq/\(aq. .TP .B ELOOP Too many links 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 .BR 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 .IR target , or a prefix of .IR source , 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 VERSIONS The definitions of .BR MS_DIRSYNC , .BR MS_MOVE , .BR MS_REC , .BR MS_RELATIME , and .BR MS_STRICTATIME were only added to glibc headers in version 2.12. .\" FIXME: Definitions of the so-far-undocumented MS_UNBINDABLE, MS_PRIVATE, .\" MS_SHARED, and MS_SLAVE were (also) only added to glibc headers in 2.12. .SH "CONFORMING TO" This function is Linux-specific and should not be used in programs intended to be portable. .SH NOTES The original .B MS_SYNC flag was renamed .B MS_SYNCHRONOUS in 1.1.69 when a different .B MS_SYNC was added to \fI\fP. .LP Before Linux 2.4 an attempt to execute a set-user-ID or set-group-ID program on a file system mounted with .B MS_NOSUID would fail with .BR EPERM . Since Linux 2.4 the set-user-ID and set-group-ID bits are just silently ignored in this case. .\" The change is in patch-2.4.0-prerelease. .SS Per-process Namespaces Starting with kernel 2.4.19, Linux provides per-process mount namespaces. A mount namespace is the set of file system mounts that are visible to a process. Mount-point namespaces can be (and usually are) shared between multiple processes, and changes to the namespace (i.e., mounts and unmounts) by one process are visible to all other processes sharing the same namespace. (The pre-2.4.19 Linux situation can be considered as one in which a single namespace was shared by every process on the system.) A child process created by .BR fork (2) shares its parent's mount namespace; the mount namespace is preserved across an .BR execve (2). A process can obtain a private mount namespace if: it was created using the .BR clone (2) .BR CLONE_NEWNS flag, in which case its new namespace is initialized to be a .I copy of the namespace of the process that called .BR clone (2); or it calls .BR unshare (2) with the .BR CLONE_NEWNS flag, which causes the caller's mount namespace to obtain a private copy of the namespace that it was previously sharing with other processes, so that future mounts and unmounts by the caller are invisible to other processes (except child processes that the caller subsequently creates) and vice versa. The Linux-specific .I /proc/PID/mounts file exposes the list of mount points in the mount namespace of the process with the specified ID; see .BR proc (5) for details. .SH "SEE ALSO" .BR umount (2), .BR path_resolution (7), .BR mount (8), .BR umount (8) .SH COLOPHON This page is part of release 3.44 of the Linux .I man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.