FSTAB(5)

NAME
fstab - static information about the file systems

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. The order of records in fstab is important because fsck(8), mount(8), and umount(8) sequentially iterate through fstab doing their thing.

The first field, (fs_spec), describes the special file or remote file system to be mounted. This may be a /dev/<path>, a label from a devtab(5) (typically /etc/devtab), or a <host>:<path> for NFS. Note that devtab(5) labels maybe augmented with a .suffix trailer. For example mydisk.s1a. Also note /dev based paths can mount serial numbers similar to devtab(5) labels by using the path /dev/serno/SERIALNO[.suffix].

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

The third field, (fs_vfstype), describes the type of the file system. The system can support various file system types. Only the root, /usr, and /tmp file systems need be statically compiled into the kernel; everything else will be automatically loaded at mount time. (Exception: the UFS family - FFS, MFS, and LFS cannot currently be demand-loaded.) Some people still prefer to statically compile other file systems as well.

The most common file system types are:

HAMMER
    a local HAMMER(5) file system

HAMMER2
    a local HAMMER2 file system

ufs a local ffs(5) UNIX file system

mfs a local memory-based UNIX file system

nfs a Sun Microsystems compatible “Network File System”

swap
    a disk partition to be used for swapping

msdos
    a local msdos(5) DOS compatible file system

cd9660
    a local CD-ROM file system (as per ISO 9660)

procfs
    a file system for accessing process data

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. See the options flag (-o) in the mount(8) page and the file system specific page, such as mount_nfs(8), for additional options that may be specified.

If the options ``userquota'' and/or ``groupquota'' are specified, the file system is automatically processed by the quotacheck(8) command, and 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

If the option ``noauto'' is specified, the file system will not be automatically mounted at system startup. This is recommended for all remote file systems other than NFS, since only NFS mounts are delayed until after network initialization by the rc(8) startup scripts.

Swap partitions may specify the option ``crypt'' to automatically encrypt the swap partition with a random key. Note that you will not be able to recover any kernel core dumps if you use this option.

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'' 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 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 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. File systems within a drive will be checked sequentially, but file systems 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 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_XX	"xx"	/* ignore totally */
    struct fstab {
    	char	*fs_spec;	/* block special device name */
    	char	*fs_file;	/* file system path prefix */
    	char	*fs_vfstype;	/* File system type, ufs, nfs */
    	char	*fs_mntops;	/* Mount options ala -o */
    	char	*fs_type;	/* FSTAB_* from fs_mntops */
    	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), getvfsbyname(3), HAMMER(5), dump(8), fsck(8), mount(8), quotacheck(8), quotaon(8), swapon(8), umount(8)

HISTORY
The fstab file format appeared in 4.0BSD.