How to install a Squid server

Note:
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Squid is a filtering and caching mechanism for web servers that can optimise bandwidth and performance. For more information about Squid proxy servers, refer to this guide.

Install Squid

At a terminal prompt, enter the following command to install the Squid server:

sudo apt install squid

Squid is configured by editing directives in the /etc/squid/squid.conf configuration file. The following examples illustrate a sample of directives that can be modified to configure the Squid server’s behavior. For more in-depth configuration details, see the links at the bottom of the page.

Protect the original config file

Before editing the configuration file, you should make a copy of the original and protect it from writing. You will then have the original settings as a reference, and can reuse it when needed. Run the following commands to make a copy of the original configuration file and protect it from being written to:

sudo cp /etc/squid/squid.conf /etc/squid/squid.conf.original
sudo chmod a-w /etc/squid/squid.conf.original

Change TCP port

To set your Squid server to listen on TCP port 8888 instead of the default TCP port 3128, change the http_port directive as such:

http_port 8888

Set the hostname

Change the visible_hostname directive to give the Squid server a specific hostname. This hostname does not need to be the same as the computer’s hostname. In this example it is set to weezie:

visible_hostname weezie

Configure on-disk cache

The default setting is to use on-memory cache. By changing the cache_dir directive you can configure use of an on-disk cache. The cache_dir directive takes the following arguments:

cache_dir <Type> <Directory-Name> <Fs-specific-data> [options]

In the config file you can find the default cache_dir directive commented out:

# Uncomment and adjust the following to add a disk cache directory.
#cache_dir ufs /var/spool/squid 100 16 256

You can use the default option but you can also customise your cache directory, by changing the <Type> of this directory. It can be one of the following options:

ufs: This is the common Squid storage format.
aufs: Uses the same storage format as ufs, using POSIX-threads to avoid blocking the main Squid process on disk-I/O. This was formerly known in Squid as async-io.
diskd: Uses the same storage format as ufs, using a separate process to avoid blocking the main Squid process on disk-I/O.
rock: This is a database-style storage. All cached entries are stored in a “database” file, using fixed-size slots. A single entry occupies one or more slots.

If you want to use a different directory type please take a look at their different options.

Access control

Using Squid’s access control, you can configure use of Squid-proxied Internet services to be available only to users with certain Internet Protocol (IP) addresses. For example, we will illustrate access by users of the 192.168.42.0/24 subnetwork only:

Add the following to the bottom of the ACL section of your /etc/squid/squid.conf file:
```
acl fortytwo_network src 192.168.42.0/24
```
Then, add the following to the top of the http_access section of your /etc/squid/squid.conf file:
```
http_access allow fortytwo_network
```

Using Squid’s access control features, you can configure Squid-proxied Internet services to only be available during normal business hours. As an example, we’ll illustrate access by employees of a business which is operating between 9:00AM and 5:00PM, Monday through Friday, and which uses the 10.1.42.0/24 subnetwork:

Add the following to the bottom of the ACL section of your /etc/squid/squid.conf file:
```
acl biz_network src 10.1.42.0/24
acl biz_hours time M T W T F 9:00-17:00
```
Then, add the following to the top of the http_access section of your /etc/squid/squid.conf file:
```
http_access allow biz_network biz_hours
```

Restart the Squid server

After making any changes to the /etc/squid/squid.conf file, you will need to save the file and restart the squid server application. You can restart the server using the following command:

sudo systemctl restart squid.service

Note:
If a formerly customised squid3 was used to set up the spool at /var/log/squid3 to be a mount point, but otherwise kept the default configuration, the upgrade will fail. The upgrade tries to rename/move files as needed, but it can’t do so for an active mount point. In that case you will need to adapt either the mount point or the config in /etc/squid/squid.conf so that they match.
The same applies if the include config statement was used to pull in more files from the old path at /etc/squid3/. In those cases you should move and adapt your configuration accordingly.