why reboot
 

I was quite impressed to see a database server at work has been up for 585 days (RHEL 5.5). This server is one of 5 virtual machines hosted by an IBM server using VMware.

Most of the time I read that people just leave their linux servers running and seldom reboot. Is there a practical reason why regular reboots are useful?

A reboot is mostly necessary for upgrades of the kernel, but even then there are other options, like Ksplice. If those options are not used you can be pretty sure that the machine you mentioned has all the vulnerabilities that were found in the last 585 days still wide open (and since it is running Redhat 5.5 it also misses all security updates, up to 5.9, which is the current version). You better make sure that this machine does not take connections from the web.

Kernel updates are the main reason. Updates in most other software can be handled on the fly by restarting the service.

Reboots hide bad apps.

Well most reboots are out of necessity.
Either for software that cannot upgrading while running, hardware replacement/upgrade or hung or crashed machine.

A very long uptime is the sign of a poorly maintained system. It's like bragging that you haven't changed the oil in your car for 10 years! ;)

Thanks for all the feedback:

• 5.5 -I really don't know about this. I am guessing that, as there are 48 RHEL licences, the servers were commissioned with a particular version of the OS and any upgrade would have to be strategically managed
• reboots - the server in question had a problem which was traced to a memory leak caused by a 3rd party program. So I guess take away the specific linux angle and there are a number of variables which can degrade the system. Reboots help to limit these while the 3rd party program is fixed.

Cheers

If you buy a RHEL licence (or better: subscription) you don't buy the right to run the software (like you would do with Windows, for example), but you buy support and a connection to the Red Hat Network for updates and installing software. Not updating a licensed Red Hat installation is somewhat pointless, since the updates are what you are paying for.

Reboots hide bad apps.

unless you do not count the SCHEDULED downtime


having UNSCHEDULED downtime is not good