Daemon is a computer program that runs as a background process and generally do not remains under the direct control of user. The parent process of a daemon in most cases are init, but not always.
In Linux, a Service is an application that runs in a background carrying out essential task or waiting for its execution.
Generally, there is no difference between a Daemon and a Service. Daemon is Service but service may be bigger than Daemon. Daemon provide some services and services may contain more than one Daemon.
Here in this series of Interview Article, we would be covering Services and Daemons in Linux.
1. What is Exim Service? What is the purpose of this Service?
Answer : Exim is an Open Source Mail Transfer Agent (MTA) which deals with routing, receiving and delivering of Electronic Mail. Exim service serves to be a great replacement of sendmail service which comes bundled with most of the distro.
2. What is NIS server? What is the purpose of NIS Server?
Answer : The NIS server, serves the purpose of dealing with Network Information Service which in-turn facilitates to login to other Systems with same log-in credentials. NIS is a directory service protocol which functions in Client-Server Model.
3. What will you prefer for a reverse proxy in Linux?
Answer : Reverse Proxy refers to the type of proxy that retrieves resources on account of client from server(s). The solution of ‘Reverse Proxy’ in Linux is squid as well as Apache reverse Proxy. However ‘squid’ is more preferred than ‘Apache reverse Proxy’ because of its simplicity and straight forward nature.
4. You are getting following codes (2xx, 3xx, 4xx, 5xx) in Apache, at some point of time. What does this means?
Answer : In Apache each error code points towards a specific area of problem.
- 2xx : Request of connection Successful
- 3xx: Redirection
- 4xx: Client Error
- 5xx: Server Error
5. You are asked to stop Apache Service through its control Script. What will you do?
Answer : The Apache service is controlled using a script called apachectl. In order to stop apache using its control script we need to run.
# apachectl stop [On Debian based Systems] # /etc/inid.t/httpd stop [On Red Hat based Systems]
6. How is ‘apachectl restart’ different from ‘apachectl graceful’
Answer : The ‘apachectl restart’ when executed will force Apache to restart immediately, before the task complete whereas ‘apachectl graceful’ will wait for the current task to be finished before restarting the service. Not to mention ‘apachectl graceful’ is more safe to execute but the execution time for ‘apachectl restart’ is less as compared to ‘apachectl graceful’.
7. How will you configure the nfs mounts to export it, from your local machine?
Answer : The /etc/export allows the creation of nfs exports on local machine and make it available to the whole world.
8. You are supposed to create a new Apache VirtualHost configuration for the host www.Tecmint.com that is available at /home/Tecmint/public_html/ and maintains log at /var/log/httpd/ by default.
Answer : You need to create a Apache virtual host container in main apache configuration file located at ‘/etc/httpd/conf/httpd.conf’. The following is the virtual container for host www.tecmint.com.
<VirtualHost *:80> DocumentRoot /home/Tecmint/public_html ServerName www.Tecmint.com Server Alias Tecmint.com CustomLog /var/log/httpd/Tecmint.com.log combined ErrorLog /var/log/httpd/Tecmint.com.error.log </VirtualHost>
9. You are supposed to dump all the packets of http traffic in file http.out. What will you suggest?
Answer : In order to dump all the network traffic, we need to use command ‘tcpdump’ with the following switches.
# tcpdump tcp port 80 -s0 -w http.out
10. How will you add a service (say httpd) to start at INIT Level 3?
Answer : We need to use ‘chkconfig’ tool to hook up a service at INIT Level 3 by changing its runlevel parameter.
chkconfig –level 3 httpd on
That’s all for now. I’ll be here again with another interesting article very soon. Till then stay healthy, tuned and connected to Tecmint. Don’t forget to provide us with your valuable feedback in the comment section below.