Mastering chkconfig: Control Linux Services and Runlevels with Ease

Command Overview

chkconfig is used to update, query, and modify system services for different runlevels. It acts as a switch to enable or disable services at runlevels 0‑6.

Runlevel Definitions

0 – Halt

1 – Single‑user mode

2 – Multi‑user without NFS

3 – Full multi‑user (standard)

4 – Unused

5 – X11 (graphical)

6 – Reboot

Common Commands

chkconfig --list [name]          # List services
chkconfig --add [name]            # Add service
chkconfig --del [name]            # Delete service
chkconfig --level <level> <name> on|off|reset

The --level option specifies which runlevels (e.g., 235) the service should be on or off, with priority numbers for start (on) and stop (off).

Configuration File Example

# chkconfig: 345 30 70
# description: Saves and restores system entropy pool

This header indicates the service runs at levels 3,4,5 with start priority 30 and stop priority 70.

Typical Usage Examples

# vi check.sh
chkconfig network && echo "Network service is configured"
chkconfig httpd   && echo "httpd service is configured"

# chkconfig --list
abrtd   0:off 1:off 2:off 3:off 4:off 5:off 6:off
...

# chkconfig --list | grep 3:on

# chkconfig --list | grep network

# chkconfig --add iptables
# chkconfig --list | grep iptables
iptables 0:off 1:off 2:on 3:on 4:on 5:on 6:off

# chkconfig --del iptables

# chkconfig --level 5 mysql off
# chkconfig --level 235 mysql on

Custom Service Creation

To create a custom service, place a script in /etc/init.d with a proper chkconfig header.

#!/bin/bash
# chkconfig: 345 30 70
# description: Test Service Running different level
# author: Jerry_1126
# version: v1.01

case "$1" in
  start) echo "The Test service is started!" ;;
  stop)  echo "The Test service is stopped!" ;;
  restart) echo "The Test service is restarted!" ;;
  *) echo "Invalid parameter!" ;;
esac

After making the script executable, register it with:

chmod +x /etc/init.d/test
chkconfig --add test
chkconfig --list | grep test

Appendix: Common Services

httpd – Web server

crond – Scheduled tasks

dhcpd – DHCP server

named – DNS server

nfs – NFS service

... (additional services listed)

Example: Apache httpd Init Script

#!/bin/bash
# chkconfig: 85 15
# description: Apache HTTP Server

# Load configuration
[ -f /etc/sysconfig/httpd ] && . /etc/sysconfig/httpd

apachectl=/usr/sbin/apachectl
httpd=${HTTPD-/usr/sbin/httpd}
pidfile=${PIDFILE-/var/run/httpd.pid}
lockfile=${LOCKFILE-/var/lock/subsys/httpd}

start() {
  echo -n "Starting $prog: "
  LANG=$HTTPD_LANG daemon --pidfile=$pidfile $httpd $OPTIONS
  RETVAL=$?
  [ $RETVAL -eq 0 ] && touch $lockfile
  return $RETVAL
}
# ... (rest of script omitted for brevity)

The script demonstrates typical start, stop, reload, and status functions for managing the Apache service.