OpenBSD manual page server

Manual Page Search Parameters

FSTAB(5) File Formats Manual FSTAB(5)

fstabstatic information about the filesystems

#include <fstab.h>

The fstab file 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. Lines beginning with the ‘#’ character are comments and are ignored. The order of records in fstab is important because fsck(8) and mount(8) sequentially iterate through fstab doing their thing.

A line has the following format:

fs_spec fs_file fs_vfstype fs_mntops fs_freq fs_passno

The first field, fs_spec, describes the block special device or remote filesystem to be mounted. A block special device may be specified by pathname or by disklabel(8) UID (DUID). For filesystems of type MFS the special file name is typically that of the primary swap area; if the keyword “swap” is used instead of a special file name, default configuration parameters are used. If a program needs the character special file name, the program must create it by appending an ‘r’ after the last ‘/’ in the special file name.

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 the following types of filesystems:

An ISO 9660 CD-ROM filesystem.
A local Linux compatible ext2fs filesystem.
A local UNIX filesystem.
A local memory-based UNIX filesystem.
An MS-DOS FAT filesystem.
A Sun Microsystems compatible Network File System.
An NTFS filesystem.
A disk partition to be used for swapping.
A local memory-based UNIX filesystem.
A UDF filesystem.
A VND image file.

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 mount -a, or at system boot time). Similarly, the option “net” can be used to cause a file system to be considered only if the -N flag is passed to mount(8) or fsck(8).

If the options “userquota” and/or “groupquota” are specified, the filesystem is automatically processed by the quotacheck(8) command, and user and/or group disk quotas are enabled with quotaon(8). By default, filesystem quotas are maintained in files named quota.user and which are located at the root of the associated filesystem. These defaults may be overridden by putting an equal sign and an alternative absolute pathname following the quota option. Thus, if the user quota file for /tmp is stored in /var/quotas/tmp.user, this location can be specified as:


The type of the mount is extracted from the first parameter of 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”, “rq”, 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 by the -W and -w options of dump(8) to recommend which filesystems should be backed up. The value specifies the number of days after which a dump is regarded as being old; if it is not present, a value of zero is returned and dump(8) 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 is zero, a value of zero is returned and fsck(8) will assume that the filesystem does not need to be checked.

#define	FSTAB_RW	"rw"	/* read/write device */
#define	FSTAB_RQ	"rq"	/* read/write with quotas */
#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, rq, 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), and getfsfile(3).


Here is a sample /etc/fstab file:

/dev/sd0b none swap sw
/dev/sd1b none swap sw
/dev/sd0a / ffs rw 1 1
/dev/sd0e /var ffs rw,nodev,nosuid 1 2
#/dev/sd0f /tmp ffs rw,nodev,nosuid 1 2
swap /tmp mfs rw,nodev,nosuid,-s=153600 0 0
/dev/sd0g /usr ffs rw,nodev 1 2
/dev/sd0h /usr/local ffs rw,nodev 1 2
/dev/sd0i /home ffs rw,nodev,nosuid 1 2
/dev/sd0j /usr/src ffs rw,nodev,nosuid 1 2
/dev/cd0a /cdrom cd9660 ro,noauto 0 0
5b27c2761a9b0b06.i /mnt/key msdos rw,noauto 0 0
server:/export/ports /usr/ports nfs rw,nodev,nosuid,soft,intr 0 0

quota(1), getfsent(3), fsck(8), mount(8), quotacheck(8), quotaon(8)

The fstab file format appeared in 4.0BSD.

July 7, 2023 OpenBSD-current