How to start services on Linux

How to start services on Linux

Scripts of the services to be run in Linux are located in /etc/rc.d/init.d. To make a script start automatically at system launch, a symbolic link to the script should be created and placed in the catalog /etc/rc.d/rcN.d, where N shows the level OR  designation of script execution. 

Linux Initialization Levels – Designation

0 – system halt — the system will be stopped, 

1 – single-user mode — the system initializes minimum services and offers command line to a single user (normally, the superuser) without authentication. This mode is normally used to restore the system, 

2 – multiple-user mode — users can work on different terminals, system log-in with authentication,

3 – multiple-user network mode — unlike the level above, network is set up and various networking services are enabled,

4 – has no standard interpretation and is not generally useful;

5 – graphical subsystem start — similar to level 3, X11 graphical subsystem is also started, and system log-in is performed in graphic mode;

6 – system reboot — when this mode is on, all running applications are stopped and the system reboots

When booting, the system most often uses boot level 3 or 5. However, there is a trick in the name of the symbolic link itself, which many keep silent about, and about which I would like to tell.

Init.d

For example, /etc/rc.d/rc0.d/K60crond and /etc/rc.d/rc3.d/S40crond

indicate the same script /etc/init.d/crond of the system log service. The script starting with “K” corresponds to service shutdown, and with “S” to service start. Numbers preceding the service name provide for scripts start order in the directory. For example, script /etc/rc.d/rc3.d/S34syslogd will be started prior to script /etc/rc.d/rc3.d/S40crond, while /etc/rc.d/rc3.d/K60crond will be started prior to /etc/rc.d/rc3.d/K66syslogd. You may notice that the sum of the numbers for a service equals to 100 — this allows for organizing all scripts in the start order being reverse to that of fulfillment. Creation of symbolic links on your own is rather tiresome, so it is better to use a special utility chkconfig.

The syntax of its use is very easy:

chkconfig --list [service name]
chkconfig --add <service name>
chkconfig --del <service name>
chkconfig [--level <levels>] <service name> <on|off|reset|resetpriorities>

Where service name is the name of the running script located in /etc/rc.d/init.d

However, there is a trick here as well; the issue is that the start script should have a special format, for instance this:

#!/bin/bash
# liferayd Init script for running Liferay Java portal
# chkconfig: - 92 02
# description: Liferay Portal is the leading open source portal for the enterprise, 
# offering content management, collaboration, and social out-of-the-box.
 
if [ -f /etc/init.d/functions ] ; then
. /etc/init.d/functions
elif [ -f /etc/rc.d/init.d/functions ] ; then
. /etc/rc.d/init.d/functions
else
exit 0
fi
 
PATH=/usr/bin:/sbin:/bin:/usr/sbin
export PATH
LRHOMEDIR="/opt/local/portal/"
 
start(){
printf "Starting Portalr"
su - user -c "cd ${LRHOMEDIR}; ant start-portal"
if [ $? -eq 0 ] ; then
logger -t liferayd Portal build successfully
else
logger -t liferayd Portal build unsuccessfully
fi
}
stop(){
printf "Stoping Portalr"
su - liferay -c "cd ${LRHOMEDIR}; ant stop-portal-force"
if [ $? -eq 0 ] ; then
logger -t liferayd Portal closed successfully
else
logger -t liferayd Portal closed unsuccessfully
fi
}
restart(){
printf "Restarting Portalr"
stop
start
}
 
case "$1" in
start )
start
;;
stop)
stop
;;
restart)
restart
;;
*) printf "Usage $0 {start|stop|restart}n"
;;
esac

The script should have at least 3 potential run keys:

1. start

2. stop

3. restart

these are the basic commands that are used to start, stop and restart.

Figures are put at the very beginning of a file; they indicate the start succession:

# chkconfig: — 92 02

where 92 is a number in the start succession, and 02 is a number in the stop succession.

To add a script to the autostart list, you have to:

1. Create an executable script following the above template

2. Place the executable script in /etc/init.d

3. Run command chkconfig —add executable_script

4. Run command chkconfig executable_script on

That’s it, our portal will now start automatically with the system launch

Systemd

The configuration consists of the files named units. All units are located at:

/usr/lib/systemd/system/ – units from installed RPM packages

/run/systemd/system/ — units created in runtime

/run/systemd/system/ — units created by system administrator

 A unit is a text file:

[Name]
variable_name = value

To create a unit, you have to describe three sections: [Unit], [Service], [Install]

In the Unit section, describe:

Unit description:

Description=Liferay

Then there is a block of variables, which have an effect on the service start order:

After=mysql.service

Running mysql is required to start the service:

Requires=mysql.service

Running nginx is desirable to start the service:

Wants=nginx.service

If the service is in Requires but not in After, our service will be started in parallel to the required service

In the Service section, indicate how the service should be started:

Service type:

Type=simple

systemd suggests that the service will be started right away. The process should not be branched.

Type=forking

systemd suggests that the service is started once and the process branches with completion of the parent process.

Also, you have to determine PIDFile= so that systemd can track the main process:

PIDFile=/var/run/liferay.pid

Operation catalog, it becomes current before starting startup commands:

WorkingDirectory=/opt/local/liferay

User and group:

User=liferay
Group=liferay

Environment variables:

Environment=SERVER=production

Ban for killing the service because of lack of memory and activation of OOM mechanism:

-1000 total ban, -100 reduced probability.

OOMScoreAdjust=-100

Service start/stop and restart commands

ExecStart=/sbin/ant start-portal
ExecStop=/sbin/ant stop-portal-force
ExecReload=/sbin/ant stop-portal-force start-portal

We have a nuance here — systemd insists that the command provide the particular executable file. Full path should be given.

Timeout in seconds, indicating how long to wait for the system to fulfill start/stop commands.

TimeoutSec=300

Ask systemd to automatically restart our service if it suddenly crashes.

Control is exercised on the presence of the process from the PID file

Restart=always

In the [Install] section, describe at what run level the service should be started

Run level:

WantedBy=multi-user.target

multi-user.target or runlevel3.target corresponds to our usual runlevel=3

Unit for systemd is ready:

liferay.service

[Unit]
Description=Liferay
After=mysql.service
Requires=mysql.service
Wants=nginx.service
 
[Service]
Type=forking
PIDFile=/var/run/liferay.pid
WorkingDirectory=/opt/local/liferay
 
User=liferay
Group=liferay
 
Environment=SERVER=production
 
OOMScoreAdjust=-100
 
ExecStart=/sbin/ant start-portal
ExecStop=/sbin/ant stop-portal-force
ExecReload=/sbin/ant stop-portal-force start-portal
TimeoutSec=300
 
[Install]
WantedBy=multi-user.target

Put this file in catalog /etc/systemd/system/:

systemctl status liferay
 
myunit.service - liferay
   Loaded: loaded (/etc/systemd/system/liferay.service; disabled)
   Active: inactive (dead)
systemctl enable liferay
systemctl -l status liferay

If everything is OK, the output will be as follows:

myunit.service - liferay
   Loaded: loaded (/etc/systemd/system/liferay.service; enabled)
   Active: inactive (dead)

Start service:

systemctl start liferay

See status:

systemctl -l status liferay

Restart systemd daemon:

systemctl daemon-reload

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