bsd/man/man2/mount.2

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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 fmount,
  43 .Nm unmount
  44 .Nd mount or dismount a filesystem
  45 .Sh SYNOPSIS
  46 .Fd #include <sys/param.h>
  47 .Fd #include <sys/mount.h>
  48 .Ft int
  49 .Fn mount "const char *type" "const char *dir" "int flags" "void *data"
  50 .Ft int
  51 .Fn fmount "const char *type" "int fd" "int flags" "void *data"
  52 .Ft int
  53 .Fn unmount "const char *dir" "int flags"
  54 .Sh DESCRIPTION
  55 The
  56 .Fn mount
  57 function grafts
  58 a filesystem object onto the system file tree
  59 at the point
  60 .Ar dir .
  61 The argument
  62 .Ar data
  63 describes the filesystem object to be mounted.
  64 The argument
  65 .Ar type
  66 tells the kernel how to interpret
  67 .Ar data
  68 (See
  69 .Ar type
  70 below).
  71 The contents of the filesystem
  72 become available through the new mount point
  73 .Ar dir .
  74 Any files in
  75 .Ar dir
  76 at the time
  77 of a successful mount are swept under the carpet so to speak, and
  78 are unavailable until the filesystem is unmounted.
  79 .Pp
  80 The following
  81 .Ar flags
  82 may be specified to
  83 suppress default semantics which affect filesystem access.
  84 .Bl -tag -width MNT_SYNCHRONOUS
  85 .It Dv MNT_RDONLY
  86 The filesystem should be treated as read-only;
  87 Even the super-user may not write on it.
  88 .It Dv MNT_NOEXEC
  89 Do not allow files to be executed from the filesystem.
  90 .It Dv MNT_NOSUID
  91 Do not honor setuid or setgid bits on files when executing them.
  92 .It Dv MNT_NODEV
  93 Do not interpret special files on the filesystem.
  94 .It Dv MNT_UNION
  95 Union with underlying filesystem instead of obscuring it.
  96 .It Dv MNT_SYNCHRONOUS
  97 All I/O to the filesystem should be done synchronously.
  98 .It Dv MNT_CPROTECT
  99 Enable data protection on the filesystem if the filesystem is configured for it.
 100 .El
 101 .Pp
 102 The flag
 103 .Dv MNT_UPDATE
 104 indicates that the mount command is being applied
 105 to an already mounted filesystem.
 106 This allows the mount flags to be changed without requiring
 107 that the filesystem be unmounted and remounted.
 108 Some filesystems may not allow all flags to be changed.
 109 For example,
 110 most filesystems will not allow a change from read-write to read-only.
 111 .Pp
 112 The flag
 113 .Dv MNT_RELOAD
 114 causes the vfs subsystem to update its data structures pertaining to
 115 the specified already mounted filesystem.
 116 .Pp
 117 The
 118 .Fa type
 119 argument defines the type of the filesystem.
 120 .Pp
 121 .Fa Data
 122 is a pointer to a structure that contains the type
 123 specific arguments to mount.
 124 The format for these argument structures is described in the
 125 manual page for each filesystem.
 126 .Pp
 127 The
 128 .Fn fmount
 129 function call is equivalent to the
 130 .Fn mount
 131 function call, except in the use of the second argument.
 132 It takes an open file descriptor representing mount point
 133 instead of the string literal containing full path to the mount
 134 point in the filesystem hierarchy.
 135 .Pp
 136 The
 137 .Fn unmount
 138 function call disassociates the filesystem from the specified
 139 mount point
 140 .Fa dir .
 141 .Pp
 142 The
 143 .Fa flags
 144 argument may specify
 145 .Dv MNT_FORCE
 146 to specify that the filesystem should be forcibly unmounted even if files are
 147 still active.
 148 Active special devices continue to work,
 149 but any further accesses to any other active files result in errors
 150 even if the filesystem is later remounted.
 151 .Sh RETURN VALUES
 152 The
 153 .Fn mount
 154 and
 155 .Fn fmount
 156 return the value 0 if the mount was successful, otherwise -1 is returned
 157 and the variable
 158 .Va errno
 159 is set to indicate the error.
 160 .Pp
 161 .Nm unmount
 162 returns the value 0 if the unmount succeeded; otherwise -1 is returned
 163 and the variable
 164 .Va errno
 165 is set to indicate the error.
 166 .Sh ERRORS
 167 .Fn mount
 168 and
 169 .Fn fmount
 170 will fail when one of the following occurs:
 171 .Bl -tag -width [ENAMETOOLONG]
 172 .It Bq Er EPERM
 173 The caller is not the super-user, and the device-node and the mountpoint
 174 do not have adequate ownership and permissions.
 175 .It Bq Er ENAMETOOLONG
 176 A component of a pathname exceeded
 177 .Dv {NAME_MAX}
 178 characters, or an entire path name exceeded
 179 .Dv {PATH_MAX}
 180 characters.
 181 .It Bq Er ELOOP
 182 Too many symbolic links were encountered in translating a pathname.
 183 .It Bq Er ENOENT
 184 A component of
 185 .Fa dir
 186 does not exist.
 187 .It Bq Er ENOTDIR
 188 A component of
 189 .Ar name
 190 is not a directory,
 191 or a path prefix of
 192 .Ar special
 193 is not a directory.
 194 .It Bq Er EINVAL
 195 A pathname contains a character with the high-order bit set.
 196 .It Bq Er EBUSY
 197 Another process currently holds a reference to
 198 .Fa dir .
 199 .It Bq Er EFAULT
 200 .Fa Dir
 201 points outside the process's allocated address space.
 202 .El
 203 .Pp
 204 .Nm unmount
 205 may fail with one of the following errors:
 206 .Bl -tag -width [ENAMETOOLONG]
 207 .It Bq Er EPERM
 208 The caller is not the super-user, and the
 209 .Nm mount()
 210 was not done by the user.
 211 .It Bq Er ENOTDIR
 212 A component of the path is not a directory.
 213 .It Bq Er EINVAL
 214 The pathname contains a character with the high-order bit set.
 215 .It Bq Er ENAMETOOLONG
 216 A component of a pathname exceeded
 217 .Dv {NAME_MAX}
 218 characters, or an entire path name exceeded
 219 .Dv {PATH_MAX}
 220 characters.
 221 .It Bq Er ELOOP
 222 Too many symbolic links were encountered in translating the pathname.
 223 .It Bq Er EINVAL
 224 The requested directory is not in the mount table.
 225 .It Bq Er EBUSY
 226 A process is holding a reference to a file located
 227 on the filesystem.
 228 .It Bq Er EIO
 229 An I/O error occurred while writing cached filesystem information.
 230 .It Bq Er EFAULT
 231 .Fa Dir
 232 points outside the process's allocated address space.
 233 .El
 234 .Sh SEE ALSO
 235 .Xr mount 8 ,
 236 .Xr unmount 8 ,
 237 .Xr open 2
 238 .Sh BUGS
 239 Some of the error codes need translation to more obvious messages.
 240 .Sh HISTORY
 241 .Fn mount
 242 and
 243 .Fn unmount
 244 function calls appeared in
 245 .At v6 .
 246 .Fn fmount
 247 function call first appeared in macOS version 10.13.