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. ∗/
intmnt_freq;/∗ dump frequency, in days ∗/
intmnt_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_fsnameMust be a block special device. 

mnt_optsValid opts are: ro, rw, suid, nosuid, quota, noquota. 

NFS

mnt_fsnameThe path on the server of the directory to be served. 

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

SWAP

mnt_fsnameMust be a block special device swap partition. 

mnt_optsIgnored. 

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)

7th Edition  —  Revision 1.4 of 22/11/88