diskdev_cmds/mount.tproj/fstab.5

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  34 .\"     @(#)fstab.5     8.1 (Berkeley) 6/5/93
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  36 .Dd March 28, 2002
  37 .Dt FSTAB 5
  38 .Os Darwin
  39 .Sh NAME
  40 .Nm fstab
  41 .Nd static information about the filesystems
  42 .Sh SYNOPSIS
  43 .Fd #include <fstab.h>
  44 .Sh DESCRIPTION
  45 The file
  46 .Nm fstab
  47 contains descriptive information about the various file
  48 systems.
  49 .Nm fstab
  50 is only read by programs, and not written;
  51 it is the duty of the system administrator to properly create
  52 and maintain this file, using the
  53 .Xr vifs 8
  54 command.
  55 Each filesystem is described on a separate line;
  56 fields on each line are separated by tabs or spaces.
  57 The order of records in
  58 .Nm fstab
  59 is important because
  60 .Xr diskarbitrationd 8 ,
  61 .Xr fsck 8 ,
  62 .Xr mount 8 ,
  63 and
  64 .Xr umount 8
  65 sequentially iterate through
  66 .Nm fstab
  67 doing their thing.
  68 .Pp
  69 The first field,
  70 .Pq Fa fs_spec ,
  71 describes the block special device, the local filesystem, or
  72 the remote filesystem to be mounted.  The
  73 .Xr diskarbitrationd
  74 program supports the identification of a local filesystem uniquely by its
  75 UUID or by its volume name, irrespective of hardware configuration and of
  76 hardware parallelism, using the constructs ``UUID'' and ``LABEL''.
  77 For APFS volumes, this field should never be the block special device as it is
  78 not constant. Only the constructs ``UUID'' and ``LABEL'' should be used.
  79 .Pp
  80 The second field,
  81 .Pq Fa fs_file ,
  82 describes the mount point for the filesystem.
  83 For swap partitions, this field should be specified as ``none''.
  84 .Pp
  85 The third field,
  86 .Pq Fa fs_vfstype ,
  87 describes the type of the filesystem.
  88 The system currently supports different filesystem types, including the following:
  89 .Bl -tag -width indent -offset indent
  90 .It Em apfs
  91 APFS is the Mac OS X default filesystem since version 10.13 (High Sierra).
  92 .It Em hfs
  93 HFS+ is the previous Mac OS X default filesystem.
  94 .It Em nfs
  95 a Sun Microsystems compatible ``Network File System''
  96 .It Em msdos
  97 a DOS compatible filesystem
  98 .It Em cd9660
  99 a CD-ROM filesystem (as per ISO 9660)
 100 .It Em fdesc
 101 an implementation of /dev/fd
 102 .It Em union
 103 a translucent filesystem
 104 .El
 105 .Pp
 106 The fourth field,
 107 .Pq Fa fs_mntops ,
 108 describes the mount options associated with the filesystem.
 109 It is formatted as a comma separated list of options.
 110 It contains at least the type of mount (see
 111 .Fa fs_type
 112 below) plus any additional options
 113 appropriate to the filesystem type.
 114 .Pp
 115 The option ``auto'' can be used in the ``noauto'' form to cause
 116 a file system not to be mounted automatically (with ``mount -a'',
 117 or system boot time).
 118 .Pp
 119 The type of the mount is extracted from the
 120 .Fa fs_mntops
 121 field and stored separately in the
 122 .Fa fs_type
 123 field (it is not deleted from the
 124 .Fa fs_mntops
 125 field).
 126 If
 127 .Fa fs_type
 128 is ``rw'' or ``ro'' then the filesystem whose name is given in the
 129 .Fa fs_file
 130 field is normally mounted read-write or read-only on the
 131 specified special file.
 132 If
 133 .Fa fs_type
 134 is ``sw'' then the special file is made available as a piece of swap
 135 space by the
 136 .Xr swapon 8
 137 command at the end of the system reboot procedure.
 138 The fields other than
 139 .Fa fs_spec
 140 and
 141 .Fa fs_type
 142 are unused.
 143 If
 144 .Fa fs_type
 145 is specified as ``xx'' the entry is ignored.
 146 This is useful to show disk partitions which are currently unused.
 147 .Pp
 148 The fifth field,
 149 .Pq Fa fs_freq ,
 150 is used for these filesystems by the
 151 .Xr dump 8
 152 command to determine which filesystems need to be dumped.
 153 If the fifth field is not present, a value of zero is returned and
 154 .Xr dump
 155 will assume that the filesystem does not need to be dumped.
 156 .Pp
 157 The sixth field,
 158 .Pq Fa fs_passno ,
 159 is used by the
 160 .Xr fsck 8
 161 program to determine the order in which filesystem checks are done
 162 at reboot time.
 163 The root filesystem should be specified with a
 164 .Fa fs_passno
 165 of 1, and other filesystems should have a
 166 .Fa fs_passno
 167 of 2.
 168 Filesystems within a drive will be checked sequentially,
 169 but filesystems on different drives will be checked at the
 170 same time to utilize parallelism available in the hardware.
 171 If the sixth field is not present or zero,
 172 a value of zero is returned and
 173 .Xr fsck
 174 will assume that the filesystem does not need to be checked.
 175 .Bd -literal
 176 #define FSTAB_RW        "rw"    /* read-write device */
 177 #define FSTAB_RO        "ro"    /* read-only device */
 178 #define FSTAB_SW        "sw"    /* swap device */
 179 #define FSTAB_XX        "xx"    /* ignore totally */
 180
 181 struct fstab {
 182         char    *fs_spec;       /* block special device name */
 183         char    *fs_file;       /* filesystem path prefix */
 184         char    *fs_vfstype;    /* type of filesystem */
 185         char    *fs_mntops;     /* comma separated mount options */
 186         char    *fs_type;       /* rw, ro, sw, or xx */
 187         int     fs_freq;        /* dump frequency, in days */
 188         int     fs_passno;      /* pass number on parallel fsck */
 189 };
 190 .Ed
 191 .Pp
 192 The proper way to read records from
 193 .Pa fstab
 194 is to use the routines
 195 .Xr getfsent 3 ,
 196 .Xr getfsspec 3 ,
 197 .Xr getfstype 3 ,
 198 and
 199 .Xr getfsfile 3 .
 200 .Sh EXAMPLES
 201 .Bd -literal
 202 UUID=2A1B02AD-467D-403A-8CCD-B87E50AD3DA2 none    apfs  rw
 203 UUID=DF000C7E-AE0C-3B15-B730-DFD2EF15CB91 /export apfs  ro
 204 UUID=FAB060E9-79F7-33FF-BE85-E1D3ABD3EDEA none    hfs   rw,noauto
 205 LABEL=The\\040Volume\\040Name\\040Is\\040This none    msdos ro
 206 .Ed
 207 .Sh FILES
 208 .Bl -tag -width /etc/fstab -compact
 209 .It Pa /etc/fstab
 210 The file
 211 .Nm fstab
 212 resides in
 213 .Pa /etc .
 214 .El
 215 .Sh SEE ALSO
 216 .Xr getfsent 3 ,
 217 .Xr diskarbitrationd 8
 218 .Sh HISTORY
 219 The
 220 .Nm
 221 file format appeared in
 222 .Bx 4.0 .