Services_Management_Essentials_Devops

  ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​​​ Services​​ management​​ Essentials for Devops

What you will Learn:

  • Remove package using apt-get​​ remove

  • Remove package using apt-get purge

  • Clear cache

  • Install nginx webserver​​ (nginx​​ as background​​ service)

  • systemctl command​​ to view all services

  • systemctl command to view only running services

  • systemctl command to stop a service

  • systemctl command to start a service

  • systemctl command to view status of a service

  • Run nginx as foreground service​​ (daemon off)

  • active (exited)​​ status

Before we talk about managing services, let us see few more topics on packages.

Remove package using apt-get​​ remove

‘Remove’ method will remove the binaries but it keeps the config files. To​​ remove a package,​​ the​​ syntax​​ is:
sl apt-get remove <package name>

Remove package using apt-get purge

‘purge’ removes everything.​​ We can​​ purge and​​ free some disk space by executing​​ 
sudo apt autoremove’​​ or ‘sudo apt-get​​ autoremove

Clear cache

The command ‘sudo​​ du -sh /var/cache/apt’ tells us the amount of space currently used by cache

We can clear cache by executing ‘sudo apt-get clean

Install nginx webserver​​ (nginx​​ as background​​ service)

nginx’ is a popular webserver, let us install it​​ by executing
sudo apt-get install nginx

After installation, note down the ip address of ubuntu

Open a browser (either on your local machine host or ubuntu machine),​​ type​​ the above​​ ip address and hit ‘Enter’.​​ 

You should see nginx​​ webserver​​ running, see below.​​ So nginx​​ is running as a​​ background​​ service​​ and is serving the default webpage

systemctl command​​ to view all services​​ 

We use systemctl command to manage the services. We can execute the command ‘sudo systemctl --type=service’ to look at all the services​​ (whether running or not). Notice below nginx is running as a service

systemctl command to view only running services

We can execute the below command to look at only those services that are running:​​ 

sudo systemctl --type=service --state=running

Notice above that nginx.service is running

systemctl command to​​ stop a service

We can use ‘sudo systemctl stop <service>’ to stop a service

Refresh the webpage, notice below that nginx service is down

systemctl command to​​ start a service

We can use ‘sudo systemctl start​​ <service>’ to stop a service

Refresh the webpage, notice below that nginx service is now up

systemctl command to view​​ status of a service

We​​ can use the command to see the status of a particular service​​ sudo systemctl status <service name>

Below means that nginx service is currently ‘active (running)’. Also​​ nginx service is running as a daemon (since​​ daemon​​ is ‘on’ as you can see below)​​ viz​​ running in the​​ background

However you would see ‘inactive (dead) when you stop the service

Run nginx as foreground service​​ (daemon off)

So far we have been saying that nginx​​ service​​ is running​​ in the​​ background​​ viz​​ daemon​​ is on​​ (see the line below:
/usr/sbin/nginx –g daemon on;)

Please note that​​ /usr/sbin/nginx​​ means​​ that​​ nginx binary is present inside the path​​ /usr/sbin/

Now, we can also​​ run​​ the service​​ in the​​ foreground​​ with daemon off. Before we do that, let us first stop the service


Execute the below command to start service in foreground:

sudo /usr/sbin/nginx –g ‘daemon off;’

Refesh browser

Nginx service is now running in the foreground.

Ctrl+C to​​ kill​​ the​​ nginx​​ process

Refresh the page, notice below that foreground service is stopped​​ (since nginx webserver is not running)

Nginx generally runs in the background (daemon on), let us again restart the service in background

So, in summary, ‘daemon on’ means service is running in background and ‘daemon off’ means service is running in foreground.

active (exited)​​ status

Sometimes you might see active (exited) status

To resolve this, you can try to execute below command​​ 

After that stop the service

Next start the service

Now the status will show active (running)

Thank you for reading!

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