After the system has been running for 8 hours continuously, it becomes slow. When I faced the same situation on Windows, I used CCleaner to clean memory, which used to give me a little boost.
Is there any application or command that cleans the unused existing RAM memory (browsers, temp files, prefetch operating system files, etc.) like CCleaner does in Windows?
Best Answer
"Memory" and "temporary files" are different things.
Memory is normally RAM. Linux manages its RAM automatically, no cleaning needed; if there is some process misbehaving and using too much RAM, you just stop it. Browsers are classical offenders there; I need to close mine (and restart) every couple of weeks. Gnome-shell is another well-known memory leaker.
For the file part, you can install Ubuntu Tweak and use the janitor module:
See also How safe is Ubuntu tweak's Janitor?. You can also install it using a PPA, look here in WebUpd8 (it's still ok for 14.04).
Consider anyway that if you clear a cache, the data will need to be reloaded/rebuilt, so the effect is, most of the time, to slow things down(1). For example, clearing the nautilus thumbnails means they are to be rebuilt again --- slowing down file browsing.
(1) the only exception here is the apt-cache and the old kernels --- in normal condition, on desktop, they are almost always just lost space.
If your system is really slowing down a "rogue" or leaking application is the most common reason. Try to catch it with
topor similar tools, and if you find it, post a more specific question or a bug report.