Base service commands -

Base service commands

Last updated on: 2020-05-28

Authored by: Matthew Brown

This article describes how to manage services by using systemd.

Introduction

Many modern Linux® operating systems available at Rackspace, such as Centos® 7 and later and Ubuntu® 16.04, adopted systemd as a system manager. So you might want to know the ins and outs of how to use it to manage your applications.

Use `systemctl`

When you use systemd to manage applications, you use the command systemctl. The following sections describe several of this command’s functions.

Start and stop services

Use the command systemctl start application.service to start the application and the command systemctl stop application.service to stop the application. If you don’t know if a service is running, you can use the command systemctl status application.service to check the status, as shown in the following example:

[root@localhost ~]# systemctl status httpd.service
   httpd.service - The Apache HTTP Server
   Loaded: loaded (/usr/lib/systemd/system/httpd.service; disabled; vendor preset: disabled)
   Active: inactive (dead)
     Docs: man:httpd(8)
       man:apachectl(8)
[root@localhost ~]# systemctl start httpd.service
[root@localhost ~]# systemctl status httpd.service
  httpd.service - The Apache HTTP Server
  Loaded: loaded (/usr/lib/systemd/system/httpd.service; disabled; vendor preset: disabled)
  Active: active (running) since Sun 2020-05-24 01:30:02 UTC; 1s ago
    Docs: man:httpd(8)
       man:apachectl(8)
 Main PID: 16117 (httpd)
 Status: "Processing requests..."
 CGroup: /system.slice/httpd.service
       ├─16117 /usr/sbin/httpd -DFOREGROUND
       ├─16118 /usr/sbin/httpd -DFOREGROUND
       ├─16119 /usr/sbin/httpd -DFOREGROUND
       ├─16120 /usr/sbin/httpd -DFOREGROUND
       ├─16121 /usr/sbin/httpd -DFOREGROUND
       └─16122 /usr/sbin/httpd -DFOREGROUND

May 24 01:30:02 localhost.localdomain systemd[1]: Starting The Apache HTTP Server...
May 24 01:30:02 localhost.localdomain httpd[16117]: AH00558: httpd: Could not reliably determine
the server's fully qualified domain name, using localhost.localdomain. Set the 'ServerName' 
directive globally to suppress this message
May 24 01:30:02 localhost.localdomain systemd[1]: Started The Apache HTTP Server.
[root@localhost ~]#

Restart or reload services

Restarting and reloading a service are two separate things with systemd.

When you run the command systemctl restart application.service, the specified service restarts. If the service is in a stopped state, it starts.

When you run the command systemctl reload application.service, the configuration of the specified service reloads. For example, if you make any changes to an Apache® virtual host (vhost) and you want those changes to go live without stopping Apache, you reload the service. The new configurations take place without interrupting the service.

Enable and disable services

If you want a specific service to start when the server is booted up, run the command systemctl enable application.service. If you want to make sure a service does not start when the server boots up, run the command systemctl disable application.service.

Cloud Servers