FSTAB(5) | File Formats Manual | FSTAB(5)

# NAME

`fstab` — file system 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 file system 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.

Each configuration line/record in `fstab` has the 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 file system to be mounted. For file systems 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. (Note that for some file systems, e.g., kernfs, procfs, and tmpfs, this field has no applicable use, and any string may be supplied as a placeholder. It is present simply for consistency of argument number and order.)

If the first field is of the form “NAME=<value>” then all the dk(4) wedge partitions are searched for one that has a wedge name equal to <value> and the device corresponding to it is selected.

If the first field starts with the prefix “ROOT.” the prefix is replaced with “/dev/[root_device]”, where [root_device] is the value of the “kern.root_device” sysctl.

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

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

adosfs
  an AmigaDOS file system.
cd9660
  an ISO 9660 CD-ROM file system.
ext2fs
  an implementation of the Linux “Second Extended File-system”.
fdesc
  an implementation of /dev/fd.
ffs
  a local UNIX file system.
filecore
  a file system for RISC OS.
kernfs
  various and sundry kernel statistics.
lfs
  a log-structured file-system.
mfs
  a local memory-based UNIX file system.
msdos
  an MS-DOS “FAT file system”.
nfs
  a Sun Microsystems compatible “Network File System”.
ntfs
  a file system used by Windows NT. Still experimental.
null
  a loop-back file system, allowing parts of the system to be viewed elsewhere.
overlay
  a demonstration of layered file systems.
portal
  a general file system interface, currently supports TCP and FS mounts.
procfs
  a local file system of process information.
ptyfs
  a pseudo-terminal device file system.
swap
  a disk partition to be used for swapping and paging.
tmpfs
  an efficient memory file system.
umap
  a user and group re-mapping file system.
union
  a translucent file system.
zfs
  a ZFS file system.

The fourth field, (fs_mntops), describes the mount options associated with the file system. 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 file system 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 file system is automatically processed by the quotacheck(8) command, and legacy user and/or group disk quotas are enabled with quotaon(8). By default, file system quotas are maintained in files named quota.user and quota.group which are located at the root of the associated file system. 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

It is recommended to turn on the new, in-file system quota with tunefs(8) or at newfs(8) time, and to not use the “userquota” or “groupquota” options. Migration of limits to the new in-file system quota can be handled via quotadump(8) and quotarestore(8).

The option “rump” is used to mount the file system using a rump(3) userspace server instead of the kernel server.

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 file system 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 file systems by the dump(8) command to determine which file systems need to be dumped. If the fifth field is not present, a value of zero is returned and dump(8) will assume that the file system does not need to be dumped.

The sixth field, (fs_passno), is used by the fsck(8) program to determine the order in which file system checks are done at reboot time. The root file system should be specified with a fs_passno of 1, and other file systems should have a fs_passno of 2. Filesystems within a drive will be checked sequentially, but file systems on different drives will be checked at the same time to use 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 file system 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_DP	"dp"	/* dump device */
    #define	FSTAB_XX	"xx"	/* ignore totally */

    struct fstab {
    	char	*fs_spec;	/* block special device name */
    	char	*fs_file;	/* file system path prefix */
    	char	*fs_vfstype;	/* type of file system */
    	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), and getfsfile(3).

# FILES

/etc/fstab
  The location of `fstab` configuration file.
/usr/share/examples/fstab/
  Some useful configuration examples.

# EXAMPLES

To use “NAME” on a non-GPT disk, use:

    NAME=sb2k5Root/a        /       ffs     rw,log           1 1
    NAME=sb2k5Root/b        none    swap    sw,dp            0 0

For a gpt(8) disk, use:

    NAME=firstpartition     /       ffs     rw,log           1 1
    NAME=secondpartition    none    swap    sw,dp            0 0

# SEE ALSO

getfsent(3), getfsspecname(3), mount(8), swapctl(8)

# HISTORY

The `fstab` file format appeared in 4.0BSD.

April 19, 2020 | NetBSD 11.0