FSTAB(5) BSD File Formats Manual FSTAB(5)
NAME
fstab -- static information about the filesystems
SYNOPSIS
#include <fstab.h>
DESCRIPTION
The file fstab contains descriptive information about the various file systems. fstab is only read by programs, and not written; it is the
duty of the system administrator to properly create and maintain this file. Each filesystem is described on a separate line; fields on each
line are separated by tabs or spaces. The order of records in fstab is important because diskarbitrationd(8), fsck(8), mount(8), and
umount(8) sequentially iterate through fstab doing their thing.
The first field, (fs_spec), describes the block special device, the local filesystem, or the remote filesystem to be mounted. The
diskarbitrationd program supports the identification of a local filesystem uniquely by its UUID or by its volume name, irrespective of hard-
ware configuration and of hardware parallelism, using the constructs ``UUID'' and ``LABEL''.
The second field, (fs_file), describes the mount point for the filesystem. For swap partitions, this field should be specified as ``none''.
The third field, (fs_vfstype), describes the type of the filesystem. The system currently supports these types of filesystems:
ufs a local UNIX filesystem
nfs a Sun Microsystems compatible ``Network File System''
swap a disk partition to be used for swapping
msdos a DOS compatible filesystem
cd9660 a CD-ROM filesystem (as per ISO 9660)
procfs a file system for accessing process data
kernfs a file system for accessing kernel parameters
fdesc an implementation of /dev/fd
union a translucent filesystem
The fourth field, (fs_mntops), describes the mount options associated with the filesystem. It is formatted as a comma separated list of
options. It contains at least the type of mount (see fs_type below) plus any additional options appropriate to the filesystem type.
The option ``auto'' can be used in the ``noauto'' form to cause a file system not to be mounted automatically (with ``mount -a'', or system
boot time).
The type of the mount is extracted from the fs_mntops field and stored separately in the fs_type field (it is not deleted from the fs_mntops
field). If fs_type is ``rw'' or ``ro'' then the filesystem whose name is given in the fs_file field is normally mounted read-write or read-
only on the specified special file. If fs_type is ``sw'' then the special file is made available as a piece of swap space by the swapon(8)
command at the end of the system reboot procedure. The fields other than fs_spec and fs_type are unused. If fs_type is specified as ``xx''
the entry is ignored. This is useful to show disk partitions which are currently unused.
The fifth field, (fs_freq), is used for these filesystems by the dump(8) command to determine which filesystems need to be dumped. If the
fifth field is not present, a value of zero is returned and dump will assume that the filesystem does not need to be dumped.
The sixth field, (fs_passno), is used by the fsck(8) program to determine the order in which filesystem checks are done at reboot time. The
root filesystem should be specified with a fs_passno of 1, and other filesystems should have a fs_passno of 2. Filesystems within a drive
will be checked sequentially, but filesystems on different drives will be checked at the same time to utilize parallelism available in the
hardware. If the sixth field is not present or zero, a value of zero is returned and fsck will assume that the filesystem does not need to
be checked.
#define FSTAB_RW "rw" /* read-write device */
#define FSTAB_RO "ro" /* read-only device */
#define FSTAB_SW "sw" /* swap device */
#define FSTAB_XX "xx" /* ignore totally */
struct fstab {
char *fs_spec; /* block special device name */
char *fs_file; /* filesystem path prefix */
char *fs_vfstype; /* type of filesystem */
char *fs_mntops; /* comma separated mount options */
char *fs_type; /* rw, ro, sw, or xx */
int fs_freq; /* dump frequency, in days */
int fs_passno; /* pass number on parallel fsck */
};
The proper way to read records from fstab is to use the routines getfsent(3), getfsspec(3), getfstype(3), and getfsfile(3).
FILES
/etc/fstab The file fstab resides in /etc.
SEE ALSO
getfsent(3), diskarbitrationd(8)
HISTORY
The fstab file format appeared in 4.0BSD.
Darwin March 28, 2002 Darwin