Why does gui restarts on peak physical memory usage, though there is still plenty of virutal memory?

A common event when low on RAM occurs when the kernel OOM-killer decides to sacrifice the desktop. This loses all your unsaved work and kicks you out to a login prompt.

The sequence of events runs something like this:

1. Your system is low on memory (memory = RAM + swap)
2. An application demands more memory than the system has available.
3. The kernel responds to this demand by looking for a different application to terminate in order to free up enough memory.
4. The kernel's Out-Of-Memory-Killer (OOM-Killer) function decides that the desktop itself is a good candidate for termination.
5. Terminating the desktop returns you to the login prompt.

• This may arguably demonstrate bug in the OOM-killer. It should be killing individual applications instead of killing the entire desktop. However, it's a thorny problem to solve so don't plan on that bug being fixed rapidly.

There are a few things you can do about it:

• Track your memory usage. Use the free command to snapshot your normal RAM and swap use. Look for unxepectedly high usage. Look for unexpectedly low swap.

• Add more swap. Swap is disk space that can be used as (slower) memory pages of RAM. If you're not using swap, add some. If your swap space is insufficient, expand it. Swap is not a perfect solution: It's slow, and a sluggish system might be just as annoying.

• Reduce your use of memory-hungry applications. The big offenders for typical users are web browsers. Each tab that you're not actively watching may still be consuming vast amounts of memory. If you're low on memory, closing a few tabs might be an easy way to free up resources for more important activities.

• Add more RAM. It means spending money and opening your case, but if the free and easy changes are not enough....