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28 .\" @(#)mount.2 8.3 (Berkeley) 5/24/95
38 .Nd mount or dismount a file system
45 .Fn mount "const char *type" "const char *dir" "int flags" "void *data"
47 .Fn unmount "const char *dir" "int flags"
50 .Fn nmount "struct iovec *iov" "u_int niov" "int flags"
55 a file system object onto the system file tree
60 describes the file system object to be mounted.
63 tells the kernel how to interpret
68 The contents of the file system
69 become available through the new mount point
74 of a successful mount are swept under the carpet so to speak, and
75 are unavailable until the file system is unmounted.
79 system call behaves similarly to
81 except that the mount options (file system type name, device to mount,
82 mount-point name, etc.) are passed as an array of name-value pairs
88 The following options are required by all file systems:
89 .Bl -item -offset indent -compact
91 .Li fstype Ta file system type name (e.g., Dq Li procfs )
93 .Li fspath Ta mount point pathname (e.g., Dq Li /proc )
96 Depending on the file system type, other options may be
97 recognized or required;
98 for example, most disk-based file systems require a
100 option containing the pathname of a special device
101 in addition to the options listed above.
103 By default only the super-user may call the
106 This restriction can be removed by setting the
110 to a non-zero value; see the BUGS section for more information.
115 suppress default semantics which affect file system access.
116 .Bl -tag -width MNT_SYNCHRONOUS
118 The file system should be treated as read-only;
119 even the super-user may not write on it.
120 Specifying MNT_UPDATE without this option will upgrade
121 a read-only file system to read/write.
123 Do not allow files to be executed from the file system.
125 Do not honor setuid or setgid bits on files when executing them.
126 This flag is set automatically when the caller is not the super-user.
128 Disable update of file access times.
130 Create a snapshot of the file system.
131 This is currently only supported on UFS2 file systems, see
133 for more information.
135 Directories with the SUID bit set chown new files to their own owner.
136 This flag requires the SUIDDIR option to have been compiled into the kernel
142 pages for more information.
143 .It Dv MNT_SYNCHRONOUS
144 All I/O to the file system should be done synchronously.
146 All I/O to the file system should be done asynchronously.
148 Force a read-write mount even if the file system appears to be unclean.
154 specify that the file system is to be forcibly downgraded to a read-only
155 mount even if some files are open for writing.
156 .It Dv MNT_NOCLUSTERR
157 Disable read clustering.
158 .It Dv MNT_NOCLUSTERW
159 Disable write clustering.
164 indicates that the mount command is being applied
165 to an already mounted file system.
166 This allows the mount flags to be changed without requiring
167 that the file system be unmounted and remounted.
168 Some file systems may not allow all flags to be changed.
170 many file systems will not allow a change from read-write to read-only.
174 causes the vfs subsystem to update its data structures pertaining to
175 the specified already mounted file system.
179 argument names the file system.
180 The types of file systems known to the system can be obtained with
186 is a pointer to a structure that contains the type
187 specific arguments to mount.
188 The format for these argument structures is described in the
189 manual page for each file system.
190 By convention file system manual pages are named
191 by prefixing ``mount_'' to the name of the file system as returned by
195 file system is described by the
198 It should be noted that a manual page for default
199 file systems, known as UFS and UFS2, does not exist.
203 system call disassociates the file system from the specified
211 to specify that the file system should be forcibly unmounted
212 even if files are still active.
213 Active special devices continue to work,
214 but any further accesses to any other active files result in errors
215 even if the file system is later remounted.
221 should instead be a file system ID encoded as
222 .Dq Li FSID : Ns Ar val0 : Ns Ar val1 ,
227 are the contents of the
231 The file system that has the specified file system ID will be unmounted.
239 system calls will fail when one of the following occurs:
242 The caller is neither the super-user nor the owner of
244 .It Bq Er ENAMETOOLONG
245 A component of a pathname exceeded 255 characters,
246 or the entire length of a path name exceeded 1023 characters.
248 Too many symbolic links were encountered in translating a pathname.
261 Another process currently holds a reference to
267 points outside the process's allocated address space.
270 The following errors can occur for a
275 A component of ufs_args
282 is not a block device.
284 The major device number of
286 is out of range (this indicates no device driver exists
287 for the associated hardware).
292 No space remains in the mount table.
294 The super block for the file system had a bad magic
295 number or an out of range block size.
297 Not enough memory was available to read the cylinder
298 group information for the file system.
300 An I/O error occurred while reading the super block or
301 cylinder group information.
306 points outside the process's allocated address space.
309 The following errors can occur for a
315 timed out trying to contact the server.
317 Some part of the information described by nfs_args
318 points outside the process's allocated address space.
323 system call may fail with one of the following errors:
326 The caller is neither the super-user nor the user who issued the corresponding
329 .It Bq Er ENAMETOOLONG
330 The length of the path name exceeded 1023 characters.
332 The requested directory is not in the mount table.
334 The file system ID specified using
336 was not found in the mount table.
338 The file system ID specified using
340 could not be decoded.
342 The specified file system is the root file system.
344 A process is holding a reference to a file located
347 An I/O error occurred while writing cached file system information.
352 points outside the process's allocated address space.
357 mount can also fail if the maximum number of file systems are currently
369 functions appeared in
373 system call first appeared in
376 Some of the error codes need translation to more obvious messages.
378 Allowing untrusted users to mount arbitrary media, e.g. by enabling
380 should not be considered safe.
383 were not built to safeguard against malicious devices.