Mark Hahn wrote: >> Somehow it works on Fedora 10, but not on CentOS 4 and 5. > > what version does hdparm -v mention on each system? Hi Mark, list Better late than never: 8.6 on Fedora 10, 6.6 on CentOS 5, 5.7 on CentOS 4. I'd guess 6.6 and earlier are too old, even the man pages are different. Gus Correa