NAME

fstab − static information about filesystems

SYNOPSIS

#include <mntent.h>

DESCRIPTION

The file /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:

fsname dir type opts freq passno
for example:
/dev/xy0a / 4.2 rw,noquota 1 2

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

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 ∗/
intmnt_freq;/∗ dump frequency, in days ∗/
intmnt_passno;/∗ pass number on parallel fsck ∗/
};

Fields are separated by white space; a ‘#’ as the first non-white character indicates a comment. 

The mnt_type field determines how the mnt_fsname and 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:

4.2 mnt_fsname Must be a block special device. 
mnt_optsValid options are ro, rw, quota, noquota. 

NFS mnt_fsname The path on the server of the directory to be served. 
mnt_optsValid options are ro, rw, quota, noquota, hard, soft. 

SWAP mnt_fsname Must be a block special device swap partition. 
mnt_optsIgnored. 

If the mnt_type is specified as ignore then the entry is ignored.  This is useful to show disk partitions not currently used. 

The field mnt_freq indicates how often each partition should be dumped by the dump(8) command (and triggers that command’s w option, which determines what filesystems should be dumped).  Most systems set the mnt_freq field to 1, indicating that filesystems are dumped each day. 

The final field mnt_passno is used by the consistency checking program fsck(8) to allow overlapped checking of filesystems during a reboot. All filesystems with mnt_passno of 1 are checked first simultaneously, then all filesystems with mnt_passno of 2, and so on.  It is usual to make the 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. 

The /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 /etc/fstab is important because fsck, mount, and umount process the file sequentially; filesystems must appear after filesystems they are mounted within. 

FILES

/etc/fstab

SEE ALSO

getmntent(3), fsck(8), mount(8), quotacheck(8), quotaon(8)

Sun Release 2.0  —  Last change: 12 March 1985