MNTENT(5)

NAME
mntent, fstab - static information about filesystems

SYNOPSIS
#include <mntent.h>

DESCRIPTION
The file /etc/fstab describes the file systems and swapping partitions used by the local machine. It is created by the system administrator using a text editor and processed by commands which mount, unmount, check consistency of, dump and restore file systems, and by the system in providing swap space.

It consists of a number of lines of the form:

    fsname dir type opts freq passno

an example of which would be:

    /dev/xy0a / 4.3 rw,noquota 1 2

The entries in this file are accessed using the routines in getmntent(3), which returns a structure of the following form:

    struct mntent {
    	char	*mnt_fsname;	/* file system name */
    	char	*mnt_dir;	/* file system path prefix */
    	char	*mnt_type;	/* 4.3, nfs, swap, or ignore */
    	char	*mnt_opts;	/* ro, quota, etc. */
    	int	mnt_freq;	/* dump frequency, in days */
    	int	mnt_passno;	/* pass number on parallel fsck */
    };

There is one entry per line in the file, and the fields are separated by white space. A `#' as the first non-white character indicates a comment.

The mnt_opts field consists of a string of comma seperated options. Some of the options are common to all filesystem types, others only make sense for a single filesystem type. See mount(8) for a more complete description of the options available.

The mnt_type field determines how the mnt_fsname, and mnt_opts fields will be interpreted. Below is a list of the file system types currently supported and the way each of them interprets these fields.

4.3

    mnt_fsname
        Must be a block special device.

    mnt_opts
        Valid opts are: ro, rw, suid, nosuid, quota, noquota.

NFS

    mnt_fsname
        The path on the server of the directory to be served.

    mnt_opts
        Valid opts are: ro, rw, suid, nosuid, hard, soft, bg, fg, retry, rsize, wsize, timeo, retrans, port, intr.

SWAP

    mnt_fsname
        Must be a block special device swap partition.

    mnt_opts
        Ignored.

If the mnt_type is specified as ``ignore'' the entry is ignored. This is useful to show disk partitions which are currently not used.

The field mnt_freq indicates how often each partition should be dumped by the dump(8) command (and triggers that commands w option which tells which file systems should be dumped). Most systems set the mnt_freq field to 1 indicating that the file systems are dumped each day.

The final field mnt_passno is used by the disk consistency check program fsck(8) to allow overlapped checking of file systems during a reboot. All file systems with mnt_passno of 1 are first checked simultaneosly, then all file systems with mnt_passno of 2, and so on. It is usual to make the mnt_passno of the root file system have the value 1 and then check one file system on each available disk drive in each subsequent pass to the exhaustion of file system partitions.

/etc/fstab is only read by programs, and not written; it is the duty of the system administrator to properly create and maintain this file. The order of records in /etc/fstab is important because fsck, mount, and umount process the file sequentially; file systems must appear after file systems they are mounted within.

FILES
/etc/fstab

SEE ALSO
fsck(8), getmntent(3), mount(8), quotacheck(8), quotaon(8), umount(8)