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Service Management in Linux

Key Points of a Linux Service

  • Background Process: Runs in the background without user intervention, unlike typical applications.
  • System Management: Manages essential functions like networking, storage, logging, etc.
  • Controlled by Init Systems: Managed by an init system like systemd, upstart, or SysVinit, which controls the starting, stopping, and restarting of services.
  • Configuration and Logs: Usually have configuration files in /etc and log files in /var/log.

Managing Services Using SysVinit (/etc/init.d/)

SysVinit is an older service management system used in Debian-based and other older Linux distributions.

Checking Available Init Scripts

cd /etc/init.d/
ls -lh /etc/init.d/

Viewing an Init Script

cat /etc/init.d/<service-name>

Example:

cat /etc/init.d/apache2

Checking the Status of a Service

/etc/init.d/apache2 status

Starting or Stopping a Service

/etc/init.d/apache2 start
/etc/init.d/apache2 stop

Restarting a Service

/etc/init.d/apache2 restart

Reloading a Service

/etc/init.d/apache2 force-reload

Managing Services in Modern Linux Distributions

Using the service Command (Legacy Systems)

For older Linux distributions that use init.d or SysVinit instead of systemd:

Checking Service Status

service <service_name> status

Example:

service apache2 status

Starting a Service

service <service_name> start

Example:

service apache2 start

Stopping a Service

service <service_name> stop

Example:

service apache2 stop

Restarting a Service

service <service_name> restart

Example:

service apache2 restart

Reloading Configuration Without Restart

service apache2 reload

Managing Services with systemctl (Modern Systems)

systemctl is used in modern Linux distributions (Debian 8+, Ubuntu 15.04+, CentOS 7+, RHEL 7+).

Installing a Service (Example: HTTPD)

yum install httpd*

Checking Service Status

systemctl status <service_name>

Example:

systemctl status apache2

Starting and Stopping Services

systemctl start <service_name>
systemctl stop <service_name>

Restarting a Service

systemctl restart <service_name>

Reloading a Service

systemctl reload <service_name>

Enabling and Disabling Services at Boot

systemctl enable <service_name>
systemctl disable <service_name>

Checking if a Service is Enabled

systemctl is-enabled <service_name>

Listing Services

systemctl list-units --type=service --state=running
systemctl list-units --type=service --state=failed

Masking and Unmasking Services

Masking prevents a service from running:

systemctl mask <service_name>

Unmasking re-enables a service:

systemctl unmask <service_name>

Viewing Logs for a Service

journalctl -u <service_name>

Example:

journalctl -u httpd.service

Viewing Logs from the Last Hour

journalctl -u httpd.service --since "1 hour ago"

Live Logs (Useful for Debugging)

journalctl -u httpd.service -f

System Power Management with systemctl

Reboot the System

systemctl reboot

Shut Down the System

systemctl poweroff

Suspend the System

systemctl suspend

Hibernate the System

systemctl hibernate

SysVinit vs. Systemd (systemctl)

Modern Linux distributions use systemd, replacing SysVinit. Instead of /etc/init.d/, use:

systemctl start apache2
systemctl stop apache2
systemctl restart apache2
systemctl status apache2
systemctl enable apache2
systemctl disable apache2