Squid proxy server interview questions and answers

In this article, you will find the top 10 plus Squid Proxy Server interview questions and answers

There is a list of squid proxy server interview questions and answers and these are important if you are going for a Linux system admin interview.

Q1. What is the Proxy Server? and what is its use of it?

Ans: A proxy server works as a gateway between you and the internet. So, if you are using a proxy server and you are visiting a website, for example, linuxgurus.in, then the website linuxgurus.in will not be able to get your IP information, and it will only know the IP of the proxy server. So you can see here it is hiding the original visitor means you. With the help of this, it is protecting you from the insecure network and putting your information private.

Squid proxy server interview questions and answers
A picture to represent the Squid proxy server

Today, the proxy server does more tasks. It does not only forward the web request, but it also works as a firewall and web filter, provides shared network connections, and cache data to speed up common requests.

If you are using a good proxy server, then it will save you from evil people and keep your internal network secure.

Q2. What is the Squid proxy server?

Ans: A squid is application software that is released under GNU/GPL, it works as a proxy server and is also used for a web cache server. Squid supports HTTP, FTP, HTTPS, SSL, TLS some other protocols.

Q3. What is the default port of the Squid proxy server?

Ans: The default port of the Squid proxy server is 3128.

Q4. What is the default configuration file of Squid?

Ans: The default configuration file is located /etc/squid/squid.conf.

Q5. Can we change the Squid default port?

Ans: Yes, we can change the default port of the Squid proxy server. To change the default port we have to open the configuration file with one of the file editors like vi, vim, nano, pico, or any other editors. I am using here vim. The configuration file is located /etc/squid/squid.conf.

 sudo vim /etc/squid/squid.conf 

Now, look for the http_port 3128

Here, you can change the port from 3128 to any port which you want and save it. After saving the file restart the squid daemon to apply the changes.

sudo systemctl restart squid

Q6. How can you block some websites through the Squid proxy server?

Ans: If you want to block some website in Squid then it is a module, and you can configure for blocking the websites. The best way to block the websites in Squid by creating a black-list-websites under the directory /etc/squid.

To create a file use the below command

sudo touch /etc/squid/black-list-websites

Now open the file with any your preferred editors or use vim

sudo vim /etc/squid/black-list-websites 

Add the websites list in this file in the below way. The website’s URL depends on your choice.

.gmail.com
.yahoo.com
.google.com
.facebook.com
.instagram.com

Save the file after pressing Esc key and typing :wq and pressing Enter key. It is time to open the Squid configuration file.

sudo vim /etc/squid/squid.conf 

So, add the below lines in the last of the squid configuration file.

acl BLACKLIST dstdomain "/etc/squid/black-list-websites.acl"
http_access deny BLACKLIST

Save the configuration file and exit it. Now restart the squid service daemon.

sudo systemctl restart squid 

Q7. Is it possible to clear the cache in the Squid proxy server?

Ans: Yes, It is possible to clear the cache in the Squid proxy server. So, to make the cache clear, first, we have to stop the Squid proxy server, then we can delete it.

Firstly, use the below command to stop the Squid service daemon.

sudo systemctl stop squid

Secondly, deleting the cache file,

sudo rm -rf /var/lib/squid/cache/*<

So as now you can create a swap directory,

sudo squid -z

Q8. What is ACL in Squid?

Ans: ACL stands for Access Control List. Also, access to the internet can be controlled using ACLS. It can be controlled for allowing a group of websites, allowing for a particular time interval, caching. There are two components for the Squid ACL. i.e., ACL elements and access list. So, an access list means to allow or deny the access service.

Q9. What are the important ACL elements list in Squid?

Ans: There are some important types of ACL elements are listed below:

src: Source i.e. client’s IP addresses
dst: Destination i.e. server’s IP addresses
srcdomain: Source i.e. client’s domain name
dstdomain: Destination i.e. server’s domain name
time: Time of day and day of week
url_regex: URL regular expression pattern matching
urlpath_regex: URL-path regular expression pattern matching, leaves out the protocol and hostname
proxy_auth: User authentication through external processes
maxconn: Maximum number of connections limit from a single client IP address

So, to apply the controls, one has first to define a set of ACL and then apply rules on them. The format of an ACL statement is

acl acl_element_name type_of_acl_element values_to_acl

Q10. Is it possible to allow internet access for a particular time being?

Ans: Yes, we can allow internet access for a particular time being. for example, from Monday to Friday from 10:00 AM to 07:00 PM.

Open the Squid configuration file.

sudo vim /etc/squid/squid.conf

and add the below lines,

acl ALLOW_TIME time M T W T F 10:00-19:00
http_access allow ALLOW_TIME

So, now you can restart the squid service daemon,

$ sudo systemctl restart squid

Q11. What is the file format for the Squid data store?

Ans: The file format for the squid data store is ufs. Also, it is well known as an old squid storage format.

Q12. What is the location of cache storage in the Squid?

Ans: The squid stores cache in /var/spool/squid.

Squid proxy server interview questions and answers

In this article, you learn questions and answers about the Squid proxy server. So, I hope you understand but, if you have any questions, you can ask in the comment section.

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