Clean up the system and remove files you no longer need
One of the great things about Linux is the large number of fantastic programs that are available. A large number are available as easy downloads from utilities like Synaptic Package Manager (Ubuntu, Mint, Debian etc.), but you can also download and install software manually.
After downloading and installing lots of programs you will end up with some software that you want to keep, but also lots of programs that are great, but aren't really useful to you personally. You will want to clean up the system by removing them. Your linux distro might include a utility to enable you to uninstall software, such as Add/Remove on the Applications menu in Ubuntu, but if that isn't available, you can also uninstall software from the Terminal command prompt. Open a Terminal window and enter something like 'sudo apt-get remove program' where 'program' is the name of the program you no longer want. Using apt-get in this way removes the program, but it doesn't remove its configuration files, so they are something you might want to find and remove manually. They are likely to be small and unimportant though.
A useful command is 'sudo apt-get clean' and this clears out the local repository of retrieved package files. Running 'sudo apt-get clean' from time to time will free up disk space.
A similar command is 'sudo apt-get autoclean' and this clears out the local repository of retrieved package files. It only removes package files that can no longer be downloaded and are no longer useful. It can be used occasionally to prevent the cache from growing too large.
Yet another related command that can be used to remove unwanted junk files from the system is 'sudo apt-get autoremove'. You know when you select a program to be installed and the system says it needs to install x, y and z because it depends on them? Well this command is used to remove packages that were automatically installed to satisfy dependencies for some program and that are no longer needed.
There is an alternative to all this command line stuff and that is to use Computer Janitor (on the System, Administration menu in Ubuntu). Run this and it will scan the system for cruft. Cruft is what it calls files that aren't needed, such as packages that were installed because some software specified it as a dependency and now nothing depends on it, packages that the OS no longer uses, and so on. It's very easy to use and it lists the items it finds, allows you to deselect any you want to keep, then removes the rest when you click the Cleanup button. It sounds like the perfect tool for cleaning up the system, but some people have reported that it has removed too much and one or more programs don't work afterwards. Take care when using it and look at the list of items to be removed very carefully.
Of course, this being linux, we can run Computer Janitor from the Terminal command line prompt. Enter 'sudo computer-janitor' and you'll see a list of command line switches. For example, you can use 'sudo computer-janitor find' to see what it can find, then 'sudo computer-janitor cleanup' to actually remove the junk files. Add the name of an actual program to the end of the cleanup command and it will remove only that item.
Another utility you can use is BleachBit. This is a cleanup utility that erases various caches, delete cookies, clears internet history, removes unused localisations, shreds logs, and deletes temporary files. It doesn't remove anything you can't live without, so it's safe to use and all it does is clear out logs and caches.
Installing BleachBit is easy and you can use Synaptic Package Manager in Ubuntu, type 'sudo yum install bleachbit' into Fedora and so on. However, these may not be the latest versions and it is much better to download the appropriate deb or rpm package from the author's website.
Using BleachBit is also easy and the left-hand pane lists all the categories of items it can clean up, such as APT, Bash, Firefox, Nautilus, OpenOffice, System and so on. You just tick the ones you want to clean and click the Preview button in the toolbar. A list of files is displayed and if you are happy to proceed you click the Delete button.