chkconfig Command Linux: Complete Guide to System Service Management

The chkconfig command is a powerful system administration tool in Red Hat-based Linux distributions that allows you to configure system services to start automatically at different runlevels. While modern systems have largely migrated to systemctl, understanding chkconfig remains crucial for managing legacy systems and understanding Linux service architecture.

What is chkconfig?

chkconfig is a command-line utility that provides a simple way to maintain the /etc/rc[0-6].d directory structure. It’s primarily used on Red Hat Enterprise Linux (RHEL), CentOS, and Fedora systems to:

• Enable or disable system services
• Configure services for specific runlevels
• Query the current status of services
• Add or remove services from the chkconfig management

Understanding Linux Runlevels

Before diving into chkconfig usage, it’s essential to understand Linux runlevels:

Basic chkconfig Syntax

The basic syntax of the chkconfig command follows this pattern:

chkconfig [options] [service_name] [on|off|reset]

Installing chkconfig

On most Red Hat-based systems, chkconfig comes pre-installed. If it’s missing, you can install it using:

# On RHEL/CentOS/Fedora
sudo yum install chkconfig

# On newer systems with DNF
sudo dnf install chkconfig

Essential chkconfig Commands

1. Listing All Services

To view all services and their current status across all runlevels:

chkconfig --list

Sample Output:

NetworkManager  0:off   1:off   2:on    3:on    4:on    5:on    6:off
acpid          0:off   1:off   2:on    3:on    4:on    5:on    6:off
atd            0:off   1:off   2:off   3:on    4:on    5:on    6:off
auditd         0:off   1:off   2:on    3:on    4:on    5:on    6:off
crond          0:off   1:off   2:on    3:on    4:on    5:on    6:off

2. Checking Specific Service Status

To check the status of a specific service:

chkconfig --list httpd

Sample Output:

httpd          0:off   1:off   2:off   3:off   4:off   5:off   6:off

3. Enabling a Service

To enable a service to start automatically at boot:

sudo chkconfig httpd on

This enables the service for runlevels 2, 3, 4, and 5 by default.

4. Disabling a Service

To disable a service from starting automatically:

sudo chkconfig httpd off

5. Configuring Specific Runlevels

To enable or disable a service for specific runlevels:

# Enable httpd only for runlevels 3 and 5
sudo chkconfig --level 35 httpd on

# Disable httpd for runlevel 5
sudo chkconfig --level 5 httpd off

Advanced chkconfig Operations

Adding a Custom Service

Before using chkconfig with a custom service, the service script must include specific headers:

#!/bin/bash
# chkconfig: 35 80 20
# description: My Custom Service
#
# The first line after the shebang must contain:
# chkconfig: [runlevels] [start_priority] [stop_priority]

To add a service to chkconfig management:

sudo chkconfig --add myservice

Removing a Service

To remove a service from chkconfig management:

sudo chkconfig --del myservice

Resetting Service Configuration

To reset a service to its default configuration:

sudo chkconfig httpd reset

Working with SysV Init Scripts

chkconfig works with System V init scripts located in /etc/init.d/. Here’s how to create a compatible service script:

#!/bin/bash
# chkconfig: 35 99 99
# description: Sample service script
#
. /etc/rc.d/init.d/functions

case "$1" in
start)
    echo -n "Starting myservice: "
    daemon /usr/local/bin/myservice
    RETVAL=$?
    echo
    [ $RETVAL -eq 0 ] && touch /var/lock/subsys/myservice
    ;;
stop)
    echo -n "Shutting down myservice: "
    pid=`ps -aefw | grep DAEMON | grep -v " grep " | awk '{print $2}'`
    kill -9 $pid
    [ $? -eq 0 ] && echo "OK" || echo "Failed"
    ;;
*)
    echo "Usage: {start|stop}"
    exit 1
esac

exit $?

Common Use Cases and Examples

Web Server Configuration

Setting up Apache HTTP server to start automatically:

# Install Apache
sudo yum install httpd

# Enable Apache for automatic startup
sudo chkconfig httpd on

# Verify the configuration
chkconfig --list httpd

# Start the service immediately
sudo service httpd start

Database Service Management

Configuring MySQL/MariaDB service:

# Enable MySQL for runlevels 3 and 5 only
sudo chkconfig --level 35 mysqld on

# Check current status
chkconfig --list mysqld

# Disable for all runlevels
sudo chkconfig mysqld off

Network Services

Managing network-related services:

# Enable SSH daemon
sudo chkconfig sshd on

# Configure firewall service for specific runlevels
sudo chkconfig --level 345 iptables on

# Disable unnecessary services
sudo chkconfig bluetooth off
sudo chkconfig cups off

Troubleshooting Common Issues

Service Not Listed

If a service doesn’t appear in chkconfig --list:

1. Check if the service script exists in /etc/init.d/
2. Verify the script has proper chkconfig headers
3. Add the service manually: sudo chkconfig --add servicename

Permission Denied Errors

Always use sudo when modifying service configurations:

# Correct way
sudo chkconfig httpd on

# This will fail
chkconfig httpd on

Service Fails to Start

If a service is enabled but fails to start:

# Check service status
service servicename status

# Review system logs
tail -f /var/log/messages

# Check service-specific logs
tail -f /var/log/httpd/error_log

chkconfig vs systemctl

Modern Linux distributions use systemd instead of SysV init. Here’s a comparison:

Best Practices and Security Considerations

1. Principle of Least Privilege

Only enable services that are absolutely necessary:

# Audit currently enabled services
chkconfig --list | grep ":on"

# Disable unnecessary services
sudo chkconfig unwanted-service off

2. Regular Service Auditing

Create a script to regularly audit service configurations:

#!/bin/bash
# Service audit script
echo "=== Enabled Services ==="
chkconfig --list | grep "3:on" | awk '{print $1}'

echo "=== Running Services ==="
service --status-all 2>/dev/null | grep running

3. Backup Service Configurations

Before making changes, backup current configurations:

# Create backup of current service states
chkconfig --list > /root/chkconfig-backup-$(date +%Y%m%d).txt

Performance Optimization

Boot Time Optimization

Improve system boot time by disabling unnecessary services:

# Common services that can be safely disabled on servers
sudo chkconfig bluetooth off
sudo chkconfig cups off
sudo chkconfig avahi-daemon off
sudo chkconfig ModemManager off

Service Dependencies

Understand service dependencies before disabling:

# Check what services depend on a particular service
grep -r "Required-Start.*servicename" /etc/init.d/

Monitoring and Logging

Service Status Monitoring

Create monitoring scripts to track service states:

#!/bin/bash
# Monitor critical services
SERVICES="httpd mysqld sshd"

for service in $SERVICES; do
    if chkconfig --list $service | grep -q "3:on"; then
        echo "$service is enabled"
    else
        echo "WARNING: $service is not enabled!"
    fi
done

Migration Strategies

When migrating from chkconfig to systemctl:

1. Document current service configurations
2. Create equivalent systemd service files
3. Test thoroughly in a development environment
4. Plan rollback procedures

# Document current chkconfig state
chkconfig --list > current-services.txt

# For each enabled service, create systemd equivalent
sudo systemctl enable servicename.service

Conclusion

The chkconfig command remains an essential tool for Linux system administrators, especially when working with Red Hat-based systems or legacy infrastructure. While systemd has become the standard init system for modern Linux distributions, understanding chkconfig provides valuable insights into system service management and ensures compatibility with older systems.

Key takeaways include:

• Always use sudo when modifying service configurations
• Regularly audit enabled services for security
• Understand runlevels and their implications
• Follow the principle of least privilege
• Plan migration strategies for modern systems

By mastering chkconfig, you’ll have the skills necessary to effectively manage system services, optimize boot performance, and maintain secure, efficient Linux systems across various enterprise environments.