What's this?

commandlinefu.com is the place to record those command-line gems that you return to again and again.

Delete that bloated snippets file you've been using and share your personal repository with the world. That way others can gain from your CLI wisdom and you from theirs too. All commands can be commented on, discussed and voted up or down.

If you have a new feature suggestion or find a bug, please get in touch via http://commandlinefu.uservoice.com/

Get involved!

You can sign-in using OpenID credentials, or register a traditional username and password.

First-time OpenID users will be automatically assigned a username which can be changed after signing in.

Universal configuration monitoring and system of record for IT.

Stay in the loop…

Follow the Tweets.

Every new command is wrapped in a tweet and posted to Twitter. Following the stream is a great way of staying abreast of the latest commands. For the more discerning, there are Twitter accounts for commands that get a minimum of 3 and 10 votes - that way only the great commands get tweeted.

» http://twitter.com/commandlinefu
» http://twitter.com/commandlinefu3
» http://twitter.com/commandlinefu10

Subscribe to the feeds.

Use your favourite RSS aggregator to stay in touch with the latest commands. There are feeds mirroring the 3 Twitter streams as well as for virtually every other subset (users, tags, functions,…):

Subscribe to the feed for:



May 19, 2015 - A Look At The New Commandlinefu
I've put together a short writeup on what kind of newness you can expect from the next iteration of clfu. Check it out here.
March 2, 2015 - New Management
I'm Jon, I'll be maintaining and improving clfu. Thanks to David for building such a great resource!

Top Tags





clean up memory on linux

Terminal - clean up memory on linux
sync; echo 3 | sudo tee /proc/sys/vm/drop_caches
2010-05-23 11:39:35
User: bandie91
Functions: echo sudo sync tee
clean up memory on linux

where proc filesystem mounted under /proc


There is 1 alternative - vote for the best!

Terminal - Alternatives
sync && echo 3 | sudo tee /proc/sys/vm/drop_caches
sync; echo 3 > /proc/sys/vm/drop_caches
sysctl -w vm.drop_caches=3
sudo sync && sudo echo 3 | sudo tee /proc/sys/vm/drop_caches
2012-03-17 08:27:58
User: StephenJudge
Functions: echo sudo sync tee
Tags: memory cache

"That's it. Not much to see here. The first command writes any cache data that hasn't been written to the disk out to the disk. The second command tells the kernel to drop what's cached. Not much to it. This invalidates the write cache as well as the read cache, which is why we have the sync command first. Supposedly, it is possible to have some cached write data never make it to disk, so use it with caution, and NEVER do it on a production server. You could ... but why take the risk?

As long as you are running a post 2.6.16 kernel,..."

Source: http://ubuntuforums.org/showpost.php?p=3621283&postcount=1

sync; echo 3 > /proc/sys/vm/drop_caches
2011-04-26 21:12:06
User: renich
Functions: echo sync

It clears caches from memory. It works fine on CentOS and Fedora. It will show you how much memory you need, for real.

Know a better way?

If you can do better, submit your command here.

What others think

Why would you want to do this?

Comment by DNSpyder 288 weeks ago

Nice, but what would you use it for other than prettying up /usr/bin/free for management's consumption?

Comment by sufoo 288 weeks ago

Buffers and caches in linux only use unused memory, i.e. memory not used by processes. So it's incorrect to think that you are making more memory available for programs by using this, in general. As soon as an application makes a big memory request, the kernel may satisfy that request by "dropping" enough buffers or cache to satisfy the request. Because unused memory is a terrible thing to waste. :-) If you do this, and then want to cache a file's contents (if there is memory available) then simply do

cat filename > /dev/null

if you run htop you can see the cache fill up as cat reads this file and automatically uses cache if it can.

Comment by bwoodacre 288 weeks ago

bwoodacre: its news for me.

i had hope it decrease number of pagefaults

Comment by bandie91 287 weeks and 6 days ago

under what situation i should use this command??

Comment by criver 286 weeks and 1 day ago

Your point of view

You must be signed in to comment.