[cd34]

once a never. Unless there is a kernel security patch, and then only after you have updated another bunch of non-critical machines to test stability.

And a while back, there were a bunch of kernel security patches, some quite nasty. If you're not running a relatively recent 2.4.28 + grsec or another security framework, you should be running 2.4.29.

uname -a at the shell prompt to see your kernel version.

Some are only local exploits, so, if you're not on a virtual server sharing it with other people, you don't need some of the more recent patches.

If your host is running <=2.6.9, there are some stability & security issues fixed in later kernels.