FSTAB(5)

NAME
fstab - filesystem table for devices, types, and mount points

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. Lines beginning with “#” are comments. The order of records in fstab is important because fsck(8), mount(8), and umount(8) sequentially iterate through fstab doing their respective tasks.

The first field, (fs_spec), describes the block special device or remote filesystem to be mounted. For filesystems of type ffs, the special file name is the block special file name, and not the character special file name. If a program needs the character special file name, the program must create it by appending a “r” after the last “/” in the special file name.

The second field, (fs_file), describes the mount point for the filesystem. For swap and dump partitions, this field should be specified as “none”.

The third field, (fs_vfstype), describes the type of the filesystem. The system currently supports these filesystems:

adosfs
    an AmigaDOS filesystem

cd9660
    an ISO 9660 CD-ROM filesystem

ext2fs
    an implementation of the Linux “Second Extended File-system”.

fdesc
    an implementation of /dev/fd

ffs a local UNIX filesystem

kernfs
    various and sundry kernel statistics

lfs a log-structured file-system. Currently does not work.

mfs a local memory-based UNIX filesystem

msdos
    an MS-DOS “FAT filesystem”

nfs a Sun Microsystems compatible “Network File System”

nullfs
    a loop-back filesystem, allowing parts of the system to be viewed elsewhere.

portal
    a general filesystem interface, currently supports TCP and FS mounts.

procfs
    a local filesystem of process information

swap
    a disk partition to be used for swapping and paging

umap
    a user and group re-mapping filesystem.

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).

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 quota.group 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:

    userquota=/var/quotas/tmp.user

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” or “dp” then the special file is made available as a piece of swap or dump space by the swapctl(8) command towards the beginning of the system reboot procedure. See swapctl(8) for more information on configuring swap and dump devices. 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(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 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_RO	"ro"	/* read-only device */
    #define	FSTAB_SW	"sw"	/* swap device */
    #define	FSTAB_DP	"dp"	/* dump 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), mount_ados(8), mount_cd9660(8), mount_ext2fs(8), mount_fdesc(8), mount_ffs(8), mount_kernfs(8), mount_lfs(8), mount_mfs(8), mount_msdos(8), mount_nfs(8), mount_null(8), mount_portal(8), mount_procfs(8), mount_ufs(8), mount_umap(8), mount_union(8), swapctl(8).

HISTORY
The fstab file format appeared in 4.0BSD.