This article describes how to manage services by using systemd.
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.
When you use systemd to manage applications, you use the command
systemctl. The following sections
describe several of this command's functions.
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
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: Starting The Apache HTTP Server... May 24 01:30:02 localhost.localdomain httpd: 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: Started The Apache HTTP Server. [root@localhost ~]#
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.
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.
Updated 18 days ago