Analyze Linux disk usage

Fixing a disk space problem on a Linux server without a graphical interface is tedious without the right command line tools handy.

Disk usage

A quick df -h  lists all disks and their current usage.

Find large files

To find large folders with files to clean up, you can use ncdu. Install it ( sudo apt-get install ncdu ) and start it pointing to a certain folder.

Linux kills a process when when starving memory

I recently observed a rather strange problem with randomly dying Java processes under heavy load. The vital clue to this problem was hidden in /var/log/messages as shown below:

It turns out that Linux may decide to kill a process when the system runs out of memory. It may make sense to cap the memory limit (-Xmx) of any Java processes running on the system to a value that sums up below the server’s available memory.

Jaan Angerpikk explained this problem in great detail, follow the link below to read more on this matter.

Out of memory: Kill process or sacrifice child

Memory stats on Linux

Did you ever wonder what the VIRT, RES and SHR memory figures in top on Linux are supposed to tell you?

Here we go:

  • VIRT – How much memory the process is able to access at the moment.
  • RES – How much memory the process is actually using at the moment. This is the value you should probably be looking at and corresponds with the %MEM column.
  • SHR – How much of the VIRT memory is shareable.

Continue here if you want more details:

A peek at the man page top might also help:

Debug network traffic on a Linux server

Use the following shell command to print all traffic from and to the given IP:

This will print something like this:

This can be quite handy if you need to debug network issues.