1MOUNT(2) Linux Programmer's Manual MOUNT(2)
2
6 mount - mount file system
7
9 #include <sys/mount.h>
10 int mount(const char *source, const char *target,
12 const char *filesystemtype, unsigned long mountflags,
13 const void *data);
14
16 mount() attaches the file system specified by source (which is often a
17 device name, but can also be a directory name or a dummy) to the direc‐
18 tory specified by target.
19 Appropriate privilege (Linux: the CAP_SYS_ADMIN capability) is required
21 to mount file systems.
22 Since Linux 2.4 a single file system can be visible at multiple mount
24 points, and multiple mounts can be stacked on the same mount point.
25 Values for the filesystemtype argument supported by the kernel are
27 listed in /proc/filesystems (e.g., "minix", "ext2", "ext3", "jfs",
28 "xfs", "reiserfs", "msdos", "proc", "nfs", "iso9660"). Further types
29 may become available when the appropriate modules are loaded.
30 The mountflags argument may have the magic number 0xC0ED (MS_MGC_VAL)
32 in the top 16 bits (this was required in kernel versions prior to 2.4,
33 but is no longer required and ignored if specified), and various mount
34 flags in the low order 16 bits:
35 MS_BIND (Linux 2.4 onward)
37 Perform a bind mount, making a file or a directory subtree visi‐
38 ble at another point within a file system. Bind mounts may
39 cross file system boundaries and span chroot(2) jails. The
40 filesystemtype and data arguments are ignored. Up until Linux
41 2.6.26, mountflags was also ignored (the bind mount has the same
42 mount options as the underlying mount point).
43 MS_DIRSYNC (since Linux 2.5.19)
45 Make directory changes on this file system synchronous. (This
46 property can be obtained for individual directories or subtrees
47 using chattr(1).)
48 MS_MANDLOCK
50 Permit mandatory locking on files in this file system. (Manda‐
51 tory locking must still be enabled on a per-file basis, as
52 described in fcntl(2).)
53 MS_MOVE
55 Move a subtree. source specifies an existing mount point and
56 target specifies the new location. The move is atomic: at no
57 point is the subtree unmounted. The filesystemtype, mountflags,
58 and data arguments are ignored.
59 MS_NOATIME
61 Do not update access times for (all types of) files on this file
62 system.
63 MS_NODEV
65 Do not allow access to devices (special files) on this file sys‐
66 tem.
67 MS_NODIRATIME
69 Do not update access times for directories on this file system.
70 This flag provides a subset of the functionality provided by
71 MS_NOATIME; that is, MS_NOATIME implies MS_NODIRATIME.
72 MS_NOEXEC
74 Do not allow programs to be executed from this file system.
75 MS_NOSUID
77 Do not honor set-user-ID and set-group-ID bits when executing
78 programs from this file system.
79 MS_RDONLY
81 Mount file system read-only.
82 MS_RELATIME (Since Linux 2.6.20)
84 When a file on this file system is accessed, update the file's
85 last access time (atime) only if the current value of atime is
86 less than or equal to the file's last modification time (mtime)
87 or last status change time (ctime). This option is useful for
88 programs, such as mutt(1), that need to know when a file has
89 been read since it was last modified. Since Linux 2.6.30, the
90 kernel defaults to the behavior provided by this flag (unless
91 MS_NOATIME was specified), and the MS_STRICTATIME flag is
92 required to obtain traditional semantics. In addition, since
93 Linux 2.6.30, the file's last access time is always updated if
94 it is more than 1 day old.
95 MS_REMOUNT
97 Remount an existing mount. This allows you to change the mount‐
98 flags and data of an existing mount without having to unmount
99 and remount the file system. target should be the same value
100 specified in the initial mount() call; source and filesystemtype
101 are ignored.
102 The following mountflags can be changed: MS_RDONLY, MS_SYNCHRO‐
104 NOUS, MS_MANDLOCK; before kernel 2.6.16, the following could
105 also be changed: MS_NOATIME and MS_NODIRATIME; and, addition‐
106 ally, before kernel 2.4.10, the following could also be changed:
107 MS_NOSUID, MS_NODEV, MS_NOEXEC.
108 MS_SILENT (since Linux 2.6.17)
110 Suppress the display of certain (printk()) warning messages in
111 the kernel log. This flag supersedes the misnamed and obsolete
112 MS_VERBOSE flag (available since Linux 2.4.12), which has the
113 same meaning.
114 MS_STRICTATIME (Since Linux 2.6.30)
116 Always update the last access time (atime) when files on this
117 file system are accessed. (This was the default behavior before
118 Linux 2.6.30.) Specifying this flag overrides the effect of
119 setting the MS_NOATIME and MS_RELATIME flags.
120 MS_SYNCHRONOUS
122 Make writes on this file system synchronous (as though the
123 O_SYNC flag to open(2) was specified for all file opens to this
124 file system).
125 From Linux 2.4 onward, the MS_NODEV, MS_NOEXEC, and MS_NOSUID flags are
127 settable on a per-mount-point basis. From kernel 2.6.16 onward,
128 MS_NOATIME and MS_NODIRATIME are also settable on a per-mount-point
129 basis. The MS_RELATIME flag is also settable on a per-mount-point
130 basis.
131 The data argument is interpreted by the different file systems. Typi‐
133 cally it is a string of comma-separated options understood by this file
134 system. See mount(8) for details of the options available for each
135 filesystem type.
136
138 On success, zero is returned. On error, -1 is returned, and errno is
139 set appropriately.
140
142 The error values given below result from filesystem type independent
143 errors. Each file-system type may have its own special errors and its
144 own special behavior. See the Linux kernel source code for details.
145 EACCES A component of a path was not searchable. (See also path_reso‐
147 lution(7).) Or, mounting a read-only file system was attempted
148 without giving the MS_RDONLY flag. Or, the block device source
149 is located on a file system mounted with the MS_NODEV option.
150 EBUSY source is already mounted. Or, it cannot be remounted read-
152 only, because it still holds files open for writing. Or, it
153 cannot be mounted on target because target is still busy (it is
154 the working directory of some thread, the mount point of another
155 device, has open files, etc.).
156 EFAULT One of the pointer arguments points outside the user address
158 space.
159 EINVAL source had an invalid superblock. Or, a remount (MS_REMOUNT)
161 was attempted, but source was not already mounted on target.
162 Or, a move (MS_MOVE) was attempted, but source was not a mount
163 point, or was '/'.
164 ELOOP Too many links encountered during pathname resolution. Or, a
166 move was attempted, while target is a descendant of source.
167 EMFILE (In case no block device is required:) Table of dummy devices is
169 full.
170 ENAMETOOLONG
172 A pathname was longer than MAXPATHLEN.
173 ENODEV filesystemtype not configured in the kernel.
175 ENOENT A pathname was empty or had a nonexistent component.
177 ENOMEM The kernel could not allocate a free page to copy filenames or
179 data into.
180 ENOTBLK
182 source is not a block device (and a device was required).
183 ENOTDIR
185 target, or a prefix of source, is not a directory.
186 ENXIO The major number of the block device source is out of range.
188 EPERM The caller does not have the required privileges.
190
192 The definitions of MS_DIRSYNC, MS_MOVE, MS_REC, MS_RELATIME, and
193 MS_STRICTATIME were added to glibc headers in version 2.12.
194
196 This function is Linux-specific and should not be used in programs
197 intended to be portable.
198
200 The original MS_SYNC flag was renamed MS_SYNCHRONOUS in 1.1.69 when a
201 different MS_SYNC was added to <mman.h>.
202 Before Linux 2.4 an attempt to execute a set-user-ID or set-group-ID
204 program on a file system mounted with MS_NOSUID would fail with EPERM.
205 Since Linux 2.4 the set-user-ID and set-group-ID bits are just silently
206 ignored in this case.
207 Per-process namespaces
209 Starting with kernel 2.4.19, Linux provides per-process mount names‐
210 paces. A mount namespace is the set of file system mounts that are
211 visible to a process. Mount-point namespaces can be (and usually are)
212 shared between multiple processes, and changes to the namespace (i.e.,
213 mounts and unmounts) by one process are visible to all other processes
214 sharing the same namespace. (The pre-2.4.19 Linux situation can be
215 considered as one in which a single namespace was shared by every
216 process on the system.)
217 A child process created by fork(2) shares its parent's mount namespace;
219 the mount namespace is preserved across an execve(2).
220 A process can obtain a private mount namespace if: it was created using
222 the clone(2) CLONE_NEWNS flag, in which case its new namespace is ini‐
223 tialized to be a copy of the namespace of the process that called
224 clone(2); or it calls unshare(2) with the CLONE_NEWNS flag, which
225 causes the caller's mount namespace to obtain a private copy of the
226 namespace that it was previously sharing with other processes, so that
227 future mounts and unmounts by the caller are invisible to other pro‐
228 cesses (except child processes that the caller subsequently creates)
229 and vice versa.
230 The Linux-specific /proc/PID/mounts file exposes the list of mount
232 points in the mount namespace of the process with the specified ID; see
233 proc(5) for details.
234
236 umount(2), namespaces(7), path_resolution(7), mount(8), umount(8)
237
239 This page is part of release 3.53 of the Linux man-pages project. A
240 description of the project, and information about reporting bugs, can
241 be found at http://www.kernel.org/doc/man-pages/.
242Linux 2012-07-05 MOUNT(2)