NFSv2/usr/man/man5/fstab.5

.\" @(#)fstab.5 1.6 85/04/04 SMI;
.TH FSTAB 5 "12 March 1985"
.SH NAME
fstab \- static information about filesystems
.SH SYNOPSIS
.B #include <mntent.h>
.SH DESCRIPTION
.IX  "fstab file"  ""  "\fLfstab\fP \(em fileystem static information"
.IX  "fileystem static information"  ""  "fileystem static information \(em \fLfstab\fP"
The file
.I /etc/fstab
describes the filesystems and swapping partitions used by the local machine.
The system administrator can modify it with a text editor.
It is read by commands that mount, unmount, dump, restore,
and check the consistency of filesystems;
also by the system in providing swap space.
The file consists of a number of lines like this:
.nf
.sp .5
	\fIfsname dir type opts freq passno\fR
.sp .5
for example:
.sp .5v
	/dev/xy0a / 4.2 rw,noquota 1 2
.sp .5v
.fi
.LP
The entries from this file are accessed using the routines in
.IR getmntent (3),
which returns a structure of the following form:
.PP
.RS
.ta \w'#define'u +\w'char\0\0'u +\w'*mnt_fsname;\0\0'u
.nf
struct mntent {
	char	*mnt_fsname;	/* filesystem name */
	char	*mnt_dir;	/* filesystem path prefix */
	char	*mnt_type;	/* 4.2, nfs, swap, or ignore */
	char	*mnt_opts;	/* rw, ro, noquota, quota, hard, soft */
	int	mnt_freq;	/* dump frequency, in days */
	int	mnt_passno;	/* pass number on parallel fsck */
};
.fi
.RE
.PP
Fields are separated by white space;
a `#' as the first non-white character indicates a comment.
.PP
The
.I mnt_type
field determines how the 
.I mnt_fsname
and 
.I mnt_opts
fields will be interpreted.
Here is a list of the filesystem types currently supported,
and the way each of them interprets these fields:
.ta \w'mnt_fsname\0\0'u
.TP 10
.B 4.2
mnt_fsname	Must be a block special device.
.br
mnt_opts	Valid options are ro, rw, quota, noquota.
.TP 10
.B NFS
mnt_fsname	The path on the server of the directory to be served.
.br
mnt_opts	Valid options are ro, rw, quota, noquota, hard, soft.
.TP 10
.B SWAP
mnt_fsname	Must be a block special device swap partition.
.br
mnt_opts	Ignored.
.PP
If the
.I mnt_type
is specified as
.I ignore
then the entry is ignored.
This is useful to show disk partitions not currently used.
.PP
The field
.I mnt_freq
indicates how often each partition should be dumped by the
.IR dump (8)
command (and triggers that command's
.B w
option, which determines what filesystems should be dumped).
Most systems set the
.I mnt_freq
field to 1, indicating that filesystems are dumped each day.
.PP
The final field
.I mnt_passno
is used by the consistency checking program
.IR fsck (8)
to allow overlapped checking of filesystems during a reboot.
All filesystems with
.I mnt_passno
of 1 are checked first simultaneously,
then all filesystems with
.I mnt_passno
of 2, and so on.
It is usual to make the
.I mnt_passno
of the root filesystem have the value 1,
and then check one filesystem on each available disk drive
in each subsequent pass, until all filesystem partitions are checked.
.LP
The
.I /etc/fstab
file is read only by programs, and never written;
it is the duty of the system administrator to maintain this file.
The order of records in
.I /etc/fstab
is important because
.I fsck,
.I mount,
and
.I umount
process the file sequentially;
filesystems must appear after filesystems they are mounted within.
.SH FILES
/etc/fstab
.SH SEE ALSO
getmntent(3), fsck(8), mount(8), quotacheck(8), quotaon(8)