How To: List Open Files

Today’s article might seem unimportant and that’s okay because we’re just going to examine one way to list often files. So, in a way, it’s probably not all that important. If you are someone who wants to list open files, this would be the article for you!

For the most part, most of my readers aren’t going to want to know how to list open files because they just have no good reason to do so. It won’t be a very long article or anything. I did some long-format articles and they didn’t get much feedback. I’ll do more, but I don’t see them as needing to be all that immediate – or consistent. The shorter articles just seem to be what folks are looking for. I can live with that. (If you do like the longer articles, it’s not too late to mention that.)

Today’s tool will be one you may have never heard of. We’ll be using the right tool for the job, however. That tool will be the ‘lsof’ command. The ‘lsof’ command should be installed by default in any major distro and checking the man page will reveal that it describes itself like so:

lsof – list open files

Read that line and then look at the headline. See? I told you that it was the correct tool for the job. If you want to list open files, a tool that lists open files is the tool for the job. Imagine that?!?

List Open Files:

Of course, the lsof command is run in the terminal. As such, you’ll need an open terminal for this exercise. If you don’t know how to open the terminal, you can do so with your keyboard – just press CTRL + ALT + T and your default terminal should open.

With your terminal open, you can just run the following command which will show every currently open file (it’s a lot):

lsof

You’ll notice some of the output will say something about “permission denied”. So, if you’re going to list all the open files, you probably should use sudo with the command. Like so:

sudo lsof

Type in your password at the prompt and be prepared for the deluge of file names. It takes quite a bunch of open files for an operating system to work – and Linux treats everything like it’s a file.

So, what if you just want the output to tell you all the files opened by a specific user? The lsof command will help you out with that. Try this command:

lsof -u <username>

For example:

lsof -u kgiii

That command will show you all the files opened by that user. It’s still a lot, but it’s an easier output to process. If you wanted to show the files opened by everyone except a specific user, you’d use this command:

lsof -u ^<username>

That command would (assuming you removed the brackets) show you all the open files except those files opened by ‘username’. In any of these cases, if you see some permission denied errors you can just slap sudo on the front of it and be good to go.

Closure:

Well… If you’ve ever wanted to list open files you now know how to do so. I suppose it’d mostly be useful for things like auditing or troubleshooting performance issues. I have the command in my book of tricks, but I don’t recall ever needing to use it for much. I’ve played with lsof and it does list open files. So, there’s that.

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