Techwarelabs Community - Linux fstab file

The file fstab contains descriptive information about the various file systems. fstab is only read by programs, and not written;
Each filesystem is described on a separate line; fields on each line areseparated 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 block special device or remote filesystem to be mounted. For filesystems of type ufs, 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 filesys tem. For swap partitions, this field should be specified as ``none''.

The third field, (fs_vfstype), describes the type of the filesystem. The system can support various filesystem types. Only the root, /usr, and
/tmp filesystems 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 filesystems as well.

ufs a local UNIX filesystem

mfs a local memory-based 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 parameter

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

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 alterna
tive 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 filesystem will not be auto
matically mounted at system startup.

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 filesys
tems 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; /* 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.