man2/mount.2

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   3 .\" Copyright (C) 1993 Rickard E. Faith <faith@cs.unc.edu>
   4 .\" and Copyright (C) 1994 Andries E. Brouwer <aeb@cwi.nl>
   5 .\" and Copyright (C) 2002, 2005 Michael Kerrisk <mtk.manpages@gmail.com>
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  26 .\"
  27 .\" Modified 1996-11-04 by Eric S. Raymond <esr@thyrsus.com>
  28 .\" Modified 2001-10-13 by Michael Kerrisk <mtk.manpages@gmail.com>
  29 .\"     Added note on historical behavior of MS_NOSUID
  30 .\" Modified 2002-05-16 by Michael Kerrisk <mtk.manpages@gmail.com>
  31 .\"     Extensive changes and additions
  32 .\" Modified 2002-05-27 by aeb
  33 .\" Modified 2002-06-11 by Michael Kerrisk <mtk.manpages@gmail.com>
  34 .\"     Enhanced descriptions of MS_MOVE, MS_BIND, and MS_REMOUNT
  35 .\" Modified 2004-06-17 by Michael Kerrisk <mtk.manpages@gmail.com>
  36 .\" 2005-05-18, mtk, Added MNT_EXPIRE, plus a few other tidy-ups.
  37 .\"
  38 .TH MOUNT 2 2008-10-06 "Linux" "Linux Programmer's Manual"
  39 .SH NAME
  40 mount \- mount file system
  41 .SH SYNOPSIS
  42 .nf
  43 .B "#include <sys/mount.h>"
  44 .sp
  45 .BI "int mount(const char *" source ", const char *" target ,
  46 .BI "          const char *" filesystemtype ", unsigned long " mountflags ,
  47 .BI "          const void *" data );
  48 .fi
  49 .SH DESCRIPTION
  50 .BR mount ()
  51 attaches the file system specified by
  52 .I source
  53 (which is often a device name, but can also be a directory name
  54 or a dummy) to the directory specified by
  55 .IR target .
  56
  57 Appropriate privilege (Linux: the
  58 .B CAP_SYS_ADMIN
  59 capability) is required to mount file systems.
  60
  61 Since Linux 2.4 a single file system can be visible at
  62 multiple mount points, and multiple mounts can be stacked
  63 on the same mount point.
  64 .\" Multiple mounts on same mount point: since 2.3.99pre7.
  65
  66 Values for the
  67 .I filesystemtype
  68 argument supported by the kernel are listed in
  69 .I /proc/filesystems
  70 (like "minix", "ext2", "ext3", "jfs", "xfs", "reiserfs",
  71 "msdos", "proc", "nfs", "iso9660" etc.).
  72 Further types may become available when the appropriate modules
  73 are loaded.
  74
  75 The
  76 .I mountflags
  77 argument may have the magic number 0xC0ED (\fBMS_MGC_VAL\fP)
  78 in the top 16 bits (this was required in kernel versions prior to 2.4, but
  79 is no longer required and ignored if specified),
  80 and various mount flags (as defined in \fI<linux/fs.h>\fP for libc4 and libc5
  81 and in \fI<sys/mount.h>\fP for glibc2) in the low order 16 bits:
  82 .\" FIXME 2.6.15 added flags for "shared sub-tree" functionality:
  83 .\" MS_UNBINDABLE, MS_PRIVATE, MS_SHARED, MS_SLAVE
  84 .\" These need to be documented on this page.
  85 .\" See:
  86 .\" Documentation/filesystems/sharedsubtree.txt
  87 .\"
  88 .\" http://lwn.net/Articles/159077/
  89 .\"
  90 .\" http://myweb.sudhaa.com:2022/~ram/sharedsubtree/paper/sharedsubtree.1.pdf
  91 .\" Shared-Subtree Concept, Implementation, and Applications in Linux
  92 .\" Al Viro viro@ftp.linux.org.uk
  93 .\" Ram Pai linuxram@us.ibm.com
  94 .\"
  95 .\" http://foss.in/2005/slides/sharedsubtree1.pdf
  96 .\" Shared Subtree Concept and Implementation in the Linux Kernel
  97 .\" Ram Pai
  98 .\"
  99 .TP
 100 .BR MS_BIND " (Linux 2.4 onwards)"
 101 .\" since 2.4.0-test9
 102 Perform a bind mount, making a file or a directory subtree visible at
 103 another point within a file system.
 104 Bind mounts may cross file system boundaries and span
 105 .BR chroot (2)
 106 jails.
 107 The
 108 .IR filesystemtype
 109 and
 110 .IR data
 111 arguments are ignored.
 112 Up until Linux 2.6.26,
 113 .I mountflags
 114 was also ignored
 115 .\" with the exception of the "hidden" MS_REC mountflags bit
 116 (the bind mount has the same mount options as
 117 the underlying mount point).
 118 Since Linux 2.6.26, the
 119 .B MS_RDONLY
 120 flag is honored when making a bind mount.
 121 .TP
 122 .BR MS_DIRSYNC " (since Linux 2.5.19)"
 123 Make directory changes on this file system synchronous.
 124 (This property can be obtained for individual directories
 125 or subtrees using
 126 .BR chattr (1).)
 127 .TP
 128 .B MS_MANDLOCK
 129 Permit mandatory locking on files in this file system.
 130 (Mandatory locking must still be enabled on a per-file basis,
 131 as described in
 132 .BR fcntl (2).)
 133 .\" FIXME Say more about MS_MOVE
 134 .TP
 135 .B MS_MOVE
 136 Move a subtree.
 137 .I source
 138 specifies an existing mount point and
 139 .I target
 140 specifies the new location.
 141 The move is atomic: at no point is the subtree unmounted.
 142 The
 143 .IR filesystemtype ", " mountflags ", and " data
 144 arguments are ignored.
 145 .TP
 146 .B MS_NOATIME
 147 Do not update access times for (all types of) files on this file system.
 148 .TP
 149 .B MS_NODEV
 150 Do not allow access to devices (special files) on this file system.
 151 .TP
 152 .B MS_NODIRATIME
 153 Do not update access times for directories on this file system.
 154 This flag provides a subset of the functionality provided by
 155 .BR MS_NOATIME ;
 156 that is,
 157 .BR MS_NOATIME
 158 implies
 159 .BR MS_NODIRATIME .
 160 .TP
 161 .B MS_NOEXEC
 162 Do not allow programs to be executed from this file system.
 163 .\" (Possibly useful for a file system that contains non-Linux executables.
 164 .\" Often used as a security feature, e.g., to make sure that restricted
 165 .\" users cannot execute files uploaded using ftp or so.)
 166 .TP
 167 .B MS_NOSUID
 168 Do not honor set-user-ID and set-group-ID bits when executing
 169 programs from this file system.
 170 .\" (This is a security feature to prevent users executing set-user-ID and
 171 .\" set-group-ID programs from removable disk devices.)
 172 .TP
 173 .B MS_RDONLY
 174 Mount file system read-only.
 175 .\"
 176 .\" FIXME Document MS_REC, available since 2.4.11.
 177 .\" This flag has meaning in conjunction with MS_BIND and
 178 .\" also with the shared sub-tree flags.
 179 .TP
 180 .BR MS_RELATIME " (Since Linux 2.6.20)"
 181 When a file on this file system is accessed,
 182 only update the file's last access time (atime) if the current value
 183 of atime is less than or equal to the file's last modification time (mtime)
 184 or last status change time (ctime).
 185 This option is useful for programs, such as
 186 .BR mutt (1),
 187 that need to know when a file has been read since it was last modified.
 188 .TP
 189 .B MS_REMOUNT
 190 Remount an existing mount.
 191 This allows you to change the
 192 .I mountflags
 193 and
 194 .I data
 195 of an existing mount without having to unmount and remount the file system.
 196 .I source
 197 and
 198 .I target
 199 should be the same values specified in the initial
 200 .BR mount ()
 201 call;
 202 .I filesystemtype
 203 is ignored.
 204
 205 The following
 206 .I mountflags
 207 can be changed:
 208 .BR MS_RDONLY ,
 209 .BR MS_SYNCHRONOUS ,
 210 .BR MS_MANDLOCK ;
 211 before kernel 2.6.16, the following could also be changed:
 212 .B MS_NOATIME
 213 and
 214 .BR MS_NODIRATIME ;
 215 and, additionally, before kernel 2.4.10, the following could also be changed:
 216 .BR MS_NOSUID ,
 217 .BR MS_NODEV ,
 218 .BR MS_NOEXEC .
 219 .TP
 220 .BR MS_SILENT " (since Linux 2.6.17)"
 221 Suppress the display of certain
 222 .RI ( printk ())
 223 warning messages in the kernel log.
 224 This flag supersedes the misnamed and obsolete
 225 .BR MS_VERBOSE
 226 flag (available since Linux 2.4.12), which has the same meaning.
 227 .TP
 228 .B MS_SYNCHRONOUS
 229 Make writes on this file system synchronous (as though
 230 the
 231 .B O_SYNC
 232 flag to
 233 .BR open (2)
 234 was specified for all file opens to this file system).
 235 .PP
 236 From Linux 2.4 onwards, the
 237 .BR MS_NODEV ", " MS_NOEXEC ", and " MS_NOSUID
 238 flags are settable on a per-mount-point basis.
 239 From kernel 2.6.16 onwards,
 240 .B MS_NOATIME
 241 and
 242 .B MS_NODIRATIME
 243 are also settable on a per-mount-point basis.
 244 The
 245 .B MS_RELATIME
 246 flag is also settable on a per-mount-point basis.
 247 .PP
 248 The
 249 .I data
 250 argument is interpreted by the different file systems.
 251 Typically it is a string of comma-separated options
 252 understood by this file system.
 253 See
 254 .BR mount (8)
 255 for details of the options available for each filesystem type.
 256 .SH "RETURN VALUE"
 257 On success, zero is returned.
 258 On error, \-1 is returned, and
 259 .I errno
 260 is set appropriately.
 261 .SH ERRORS
 262 The error values given below result from filesystem type independent
 263 errors.
 264 Each filesystem type may have its own special errors and its
 265 own special behavior.
 266 See the kernel source code for details.
 267 .TP
 268 .B EACCES
 269 A component of a path was not searchable.
 270 (See also
 271 .BR path_resolution (7).)
 272 Or, mounting a read-only filesystem was attempted without giving the
 273 .B MS_RDONLY
 274 flag.
 275 Or, the block device
 276 .I source
 277 is located on a filesystem mounted with the
 278 .B MS_NODEV
 279 option.
 280 .\" mtk: Probably: write permission is required for MS_BIND, with
 281 .\" the error EPERM if not present; CAP_DAC_OVERRIDE is required.
 282 .TP
 283 .B EBUSY
 284 .I source
 285 is already mounted.
 286 Or, it cannot be remounted read-only,
 287 because it still holds files open for writing.
 288 Or, it cannot be mounted on
 289 .I target
 290 because
 291 .I target
 292 is still busy (it is the working directory of some task,
 293 the mount point of another device, has open files, etc.).
 294 .TP
 295 .B EFAULT
 296 One of the pointer arguments points outside the user address space.
 297 .TP
 298 .B EINVAL
 299 .I source
 300 had an invalid superblock.
 301 Or, a remount
 302 .RB ( MS_REMOUNT )
 303 was attempted, but
 304 .I source
 305 was not already mounted on
 306 .IR target .
 307 Or, a move
 308 .RB ( MS_MOVE )
 309 was attempted, but
 310 .I source
 311 was not a mount point, or was \(aq/\(aq.
 312 .TP
 313 .B ELOOP
 314 Too many links encountered during pathname resolution.
 315 Or, a move was attempted, while
 316 .I target
 317 is a descendant of
 318 .IR source .
 319 .TP
 320 .B EMFILE
 321 (In case no block device is required:)
 322 Table of dummy devices is full.
 323 .TP
 324 .B ENAMETOOLONG
 325 A pathname was longer than
 326 .BR MAXPATHLEN .
 327 .TP
 328 .B ENODEV
 329 .I filesystemtype
 330 not configured in the kernel.
 331 .TP
 332 .B ENOENT
 333 A pathname was empty or had a nonexistent component.
 334 .TP
 335 .B ENOMEM
 336 The kernel could not allocate a free page to copy filenames or data into.
 337 .TP
 338 .B ENOTBLK
 339 .I source
 340 is not a block device (and a device was required).
 341 .TP
 342 .B ENOTDIR
 343 .IR target ,
 344 or a prefix of
 345 .IR source ,
 346 is not a directory.
 347 .TP
 348 .B ENXIO
 349 The major number of the block device
 350 .I source
 351 is out of range.
 352 .TP
 353 .B EPERM
 354 The caller does not have the required privileges.
 355 .SH "CONFORMING TO"
 356 This function is Linux-specific and should not be used in
 357 programs intended to be portable.
 358 .SH NOTES
 359 The original
 360 .B MS_SYNC
 361 flag was renamed
 362 .B MS_SYNCHRONOUS
 363 in 1.1.69
 364 when a different
 365 .B MS_SYNC
 366 was added to \fI<mman.h>\fP.
 367 .LP
 368 Before Linux 2.4 an attempt to execute a set-user-ID or set-group-ID program
 369 on a filesystem mounted with
 370 .B MS_NOSUID
 371 would fail with
 372 .BR EPERM .
 373 Since Linux 2.4 the set-user-ID and set-group-ID bits are
 374 just silently ignored in this case.
 375 .\" The change is in patch-2.4.0-prerelease.
 376 .SH "SEE ALSO"
 377 .BR umount (2),
 378 .BR path_resolution (7),
 379 .BR mount (8),
 380 .BR umount (8)