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1.\" $OpenBSD: mount.2,v 1.6 1997/03/09 19:41:16 millert Exp $
2.\" $NetBSD: mount.2,v 1.12 1996/02/29 23:47:48 jtc Exp $
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35.\" @(#)mount.2 8.2 (Berkeley) 12/11/93
36.\"
37.Dd December 11, 1993
38.Dt MOUNT 2
39.Os BSD 4
40.Sh NAME
41.Nm mount ,
42.Nm unmount
43.Nd mount or dismount a filesystem
44.Sh SYNOPSIS
45.Fd #include <sys/param.h>
46.Fd #include <sys/mount.h>
47.Ft int
48.Fn mount "const char *type" "const char *dir" "int flags" "void *data"
49.Ft int
50.Fn unmount "const char *dir" "int flags"
51.Sh DESCRIPTION
52The
53.Fn mount
54function grafts
55a filesystem object onto the system file tree
56at the point
57.Ar dir .
58The argument
59.Ar data
60describes the filesystem object to be mounted.
61The argument
62.Ar type
63tells the kernel how to interpret
64.Ar data
65(See
66.Ar type
67below).
68The contents of the filesystem
69become available through the new mount point
70.Ar dir .
71Any files in
72.Ar dir
73at the time
74of a successful mount are swept under the carpet so to speak, and
75are unavailable until the filesystem is unmounted.
76.Pp
77The following
78.Ar flags
79may be specified to
80suppress default semantics which affect filesystem access.
81.Bl -tag -width MNT_SYNCHRONOUS
82.It Dv MNT_RDONLY
83The filesystem should be treated as read-only;
84Even the super-user may not write on it.
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85.It Dv MNT_NOEXEC
86Do not allow files to be executed from the filesystem.
87.It Dv MNT_NOSUID
88Do not honor setuid or setgid bits on files when executing them.
89.It Dv MNT_NODEV
90Do not interpret special files on the filesystem.
91.It Dv MNT_UNION
92Union with underlying filesystem instead of obscuring it.
93.It Dv MNT_SYNCHRONOUS
94All I/O to the filesystem should be done synchronously.
95.El
96.Pp
97The flag
98.Dv MNT_UPDATE
99indicates that the mount command is being applied
100to an already mounted filesystem.
101This allows the mount flags to be changed without requiring
102that the filesystem be unmounted and remounted.
103Some filesystems may not allow all flags to be changed.
104For example,
105most filesystems will not allow a change from read-write to read-only.
106.Pp
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107The flag
108.Dv MNT_RELOAD
109causes the vfs subsystem to update its data structures pertaining to
110the specified already mounted filesystem.
111.Pp
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112The
113.Fa type
114argument defines the type of the filesystem.
55e303ae 115.Pp
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116.Fa Data
117is a pointer to a structure that contains the type
118specific arguments to mount.
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119The format for these argument structures is described in the
120manual page for each filesystem.
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121.Pp
122The
123.Fn umount
124function call disassociates the filesystem from the specified
125mount point
126.Fa dir .
127.Pp
128The
129.Fa flags
130argument may specify
131.Dv MNT_FORCE
132to specify that the filesystem should be forcibly unmounted even if files are
133still active.
134Active special devices continue to work,
135but any further accesses to any other active files result in errors
136even if the filesystem is later remounted.
137.Sh RETURN VALUES
138The
139.Fn mount
140returns the value 0 if the mount was successful, otherwise -1 is returned
141and the variable
142.Va errno
143is set to indicate the error.
144.Pp
145.Nm Umount
146returns the value 0 if the umount succeeded; otherwise -1 is returned
147and the variable
148.Va errno
149is set to indicate the error.
150.Sh ERRORS
151.Fn Mount
152will fail when one of the following occurs:
153.Bl -tag -width [ENAMETOOLONG]
154.It Bq Er EPERM
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155The caller is not the super-user, and the device-node and the mountpoint
156do not have adequate ownership and permissions.
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157.It Bq Er ENAMETOOLONG
158A component of a pathname exceeded
159.Dv {NAME_MAX}
160characters, or an entire path name exceeded
161.Dv {PATH_MAX}
162characters.
163.It Bq Er ELOOP
164Too many symbolic links were encountered in translating a pathname.
165.It Bq Er ENOENT
166A component of
167.Fa dir
168does not exist.
169.It Bq Er ENOTDIR
170A component of
171.Ar name
172is not a directory,
173or a path prefix of
174.Ar special
175is not a directory.
176.It Bq Er EINVAL
177A pathname contains a character with the high-order bit set.
178.It Bq Er EBUSY
179Another process currently holds a reference to
180.Fa dir .
181.It Bq Er EFAULT
182.Fa Dir
183points outside the process's allocated address space.
184.El
185.Pp
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186.Nm Umount
187may fail with one of the following errors:
188.Bl -tag -width [ENAMETOOLONG]
189.It Bq Er EPERM
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190The caller is not the super-user, and the
191.Nm mount()
192was not done by the user.
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193.It Bq Er ENOTDIR
194A component of the path is not a directory.
195.It Bq Er EINVAL
196The pathname contains a character with the high-order bit set.
197.It Bq Er ENAMETOOLONG
198A component of a pathname exceeded
199.Dv {NAME_MAX}
200characters, or an entire path name exceeded
201.Dv {PATH_MAX}
202characters.
203.It Bq Er ELOOP
204Too many symbolic links were encountered in translating the pathname.
205.It Bq Er EINVAL
206The requested directory is not in the mount table.
207.It Bq Er EBUSY
208A process is holding a reference to a file located
209on the filesystem.
210.It Bq Er EIO
211An I/O error occurred while writing cached filesystem information.
212.It Bq Er EFAULT
213.Fa Dir
214points outside the process's allocated address space.
215.El
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216.Sh SEE ALSO
217.Xr mount 8 ,
2d21ac55 218.Xr umount 8
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219.Sh BUGS
220Some of the error codes need translation to more obvious messages.
221.Sh HISTORY
222.Fn Mount
223and
224.Fn umount
225function calls appeared in
226.At v6 .