V10/man/man5/fstab.5

.TH FSTAB 5
.CT 2 sa
.SH NAME
fstab, mtab \- information about file systems
.SH SYNOPSIS
.B #include <fstab.h>
.SH DESCRIPTION
The file
.F /etc/fstab
describes the normal configuration of file systems.
It guides the default operation of
.I mount,
.I umount,
.I swapon,
and
.IR fsck (8).
The order of records in
.F /etc/fstab
is important.
.PP
Each line of the file describes one file system.
Fields separated by colons specify
.IP
pathname of block device or other mounted object
.br
pathname of mount point
.br
file system type number
.br
integer mount flags
.br
pass number for checking; see
.IR fsck (8)
.PP
File system type numbers
and flags are listed in
.IR fmount (2).
.PP
Two special non-numeric file system types
signify things that aren't file systems:
.L xx
causes the line to be ignored,
.L sw
signifies a swap device.
.PP
Use
.IR getfsent (3)
to read data from
.LR /etc/fstab .
.PP
The file
.F /etc/mtab
lists file systems currently mounted.
Each entry is a structure of the form
.PP
.nf
.ft L
.ta 8n +27n
#define FSNMLG 32

struct mtab {
	char file[FSNMLG];\fR	mount point\fP
	char spec[FSNMLG-1];\fR	mounted object\fP
	char type;\fR	file system type\fP
};
.ft R
.fi
.SH EXAMPLES
A simple
.I fstab.
.IP
.EX
/dev/ra00:/:0:0:1
/dev/ra02:/usr:0:0:2
/dev/ra05:/tmp:0:0:3
/dev/ra10:/ra10:0:1:1
/dev/ra11::sw:0:0
/dev/ra15:/ra15:0:1:3
/dev/null:/proc:2:0:0
.EE
.SH FILES
.F /etc/fstab
.br
.F /etc/mtab
.SH SEE ALSO
.IR fmount (2),
.IR getfsent (3),
.IR mount (8)
.SH BUGS
Swap areas are not file systems,
and should not be described in
.IR fstab .
.br
For compatibility with old programs and habits,
two deprecated magic file system types survive:
.L rw
means `type 0, flag 0'
(a disk file system, mounted for reading and writing);
.L ro
means `type 0, flag 1'
(a disk file system, mounted read-only).
.br
Only file systems mounted with
.IR mount (8)
are listed in
.IR mtab .