How do you know if your system is hung?

Depending on the cause of the hang, some users on the system might be able to continue working while others see the system as dead. On some occasions, you might not be able to remotely log in, with rlogin , from another system, but will be able to log in to the system at the console. Some hung systems will respond to low-level network commands such as ping , while others will not. Finally, some systems will slow down, creeping toward the hang, giving you, the observant system administrator, a hint of what is to come, while other hangs will appear to be instantaneous.

If the system is hung, you will not see panic messages on the console. However, if you are lucky, again depending on the reason for the hang, you might see output on the console that will point you to the source of troubles. The problem could simply be that someone powered down the disks or that an Ethernet cable became disconnected.

Unfortunately, system hangs can also be caused by programming problems or bugs at the system or kernel level.

Unless you immediately locate a simple hardware problem or a rather embarrassed programmer who just discovered the side effects of running his simulation program in real time on a heavily used DBMS server, you will need to attempt to force a system panic in order to get an image of memory for analysis.