Another resource that might need our attention is the disk usage of our computer. Programs may need disk space for lots of different reasons. Installed binaries and libraries, data stored by the applications, cached information, logs, temporary files or even backups. If our computers running out of space, it's possible that we're trying to store too much data in too little space. Maybe we have too many applications installed, or we're trying to store too many large files in the drive. But it's also possible that programs are misusing the space allotted to them, like by keeping temporary files or caching information that doesn't get cleaned up quickly enough or at all. It's common for the overall performance of the system to decrease as the available disk space gets smaller. Data starts getting fragmented across the desk, and operations become slower. When a hard drive is full, programs may suddenly crash, while trying to write something into disk and finding out that they can't. A full hard drive might even lead to data loss, as some programs might truncate a file before writing an updated version of it, and then fail to write the new content, losing all the data that was stored in it before. Yikes. If it gets to this point, we'll probably see some error, like no space left on device when running our applications or in the logs. So what do you do if a computer runs out of disk space? If it's a user machine, it might be easily fixed by uninstalling applications that aren't used, or cleaning up old data that isn't needed anymore. But if it's a server, you might need to look more closely at what's going on. Is the issue that you need to add an extra drive to the server to have more available space, or is it that some application is misbehaving and filling the disk with useless data? To figure this out, you want to look at how the space is being used and what directories are taking up the most space, then drill down until you find out whether large chunks of space are taken by valid information or by files that should be perched. For example, on a database server, it's expected that the bulk of the disc space is going to be used by the data stored in the database. A mail server, it's going to be the mailboxes of the users of that service. But if you find that most of the data is stored in logs or in temporary files, something has gone wrong. One common pattern of misbehavior is a program that keeps logging error messages to the system log over and over. This can happen for lots of different reasons. For example, the OS might keep trying to start a program that fails because of a configuration problem. This will generate a new log entry with every retry, and can take up a lot of space if there are several retries per second, or it could be that the server has a lot of activity and the logs are real. But there are just too many of them. In that case, you might want to look on the tweaking, the configuration of the tools that rotate the logs more frequently, to make sure that you're keeping only what you need. In other cases, the disk might get full due to a program generating large temporary files, and then failing to clean those up. For example, an application might clean up temporary files when shutting down cleanly, but leave them behind if it crashes. Or it could simply be a programming error of creating temporary files and never cleaning them up. In a case like this, you'll ideally have some housekeeping to fix the program, and delete those files correctly. But if that's not possible, you might need to write your own script that gets rid of them. A situation that might be tricky to debug is when the files taking up the space or deleted files. I'm sure you're wondering, how can deleted files take up space? Great question. Well, if a program opens a file, the OS lets that program read and write in the file regardless of whether the file is marked as deleted or not. So lots of programs delete the temporary files they create right after opening to avoid issues with failing to clean them up later. That way, the process can read from and write to the file while the file is open. Then when the process finishes, the file gets closed and actually deleted. Now, this system is widely used and works fine for most processes. But if for some reason, this temporarily deleted file starts becoming super large, it can end up taking up all the available disk space. If that happens, we'll be left scratching our heads when trying to figure out where most of the data went, since we won't see these deleted files. To check for the specific condition, we need to list the currently opened files, and comb for the ones that we know are deleted. We include pointers to the commands for how that works in the next reading. Of course, there are all kinds of other reasons why the disk may be getting too full. Just remember that whenever this happens, your process will remain the same. You'll need to spend some time looking into what's using the disk. Check to see if it's expected or an anomaly, figure out how to solve it, and most important of all, how to prevent it from happening again? Up next, we'll discuss yet another resource that might cause some trouble. The network.
