RedHat 5 and RedHat 5.1 may hang at the final stage of reboot or shutdown because of a bug in cpufreq. A deadlock occurs when its module is unloaded, making reboot or shutdown so slow that users think the computer has frozen. This problem was fixed in RedHat 5.2. There are two workarounds for RedHat 5 and RedHat 5.1:

1. Update the kernel to the version supplied with RedHat 5.2.
2. Disable cpuspeed with the following commands.

chkconfig cpuspeed off

service cpuspeed stop

The drawback of the second method is that the system cannot use power as efficiently: it consumes more electricity than a system with cpuspeed enabled. :)