If you turn on the Xscreensaver module called Sonar while you're running a packet monitoring application (such as TCPdump), people are less likely to think you're doing anything shady, because "Only hacker tools don't have GUIs." Always hack your shell's personal configuration file (~/.bash_profile, for example) to change your shellprompt if you use GNU screen. That way you can tell what shells you've left open are single-access shells and which shells are multiplexed through a single connection with screen. It can get confusing sometimes. Because a shell run inside a GNU screen metaterminal sets an environment variable called $WINDOW, you can use that to your advantage, like this:
export PS1='\h-$WINDOW:\w \$ '
That sets your primary shellprompt to the hostname of the system you're logged into, a dash, then the metaterminal number, then a colon, then your current working directory, a space, and a $ prompt (because you're logged in as a normal user and not an admin). It'll look something like this (or at least it should):
Never try a drink called Black ICE.
If you're working on a fairly high-end system and you're trying to install Linux (for example, a Dell Poweredge), remember that Slackware has a sizable number of kernels that you can boot from - try them all. There's a good chance that at least one will bring up the integrated RAID controller. For the Dell Poweredge 4300, that'll be the raid.s kernel.
Always make sure that you get directions back from where you were. You never know when road construction will close off the only route that you know landmarks for.
DBAN - Darik's Boot and Nuke - For when you absolutely, positively have to wipe every hard drive in the room.
Always read the manual for your car to determine what size of windshield washer blades you need to buy. Some, like the Oldsmobile, have two different lengths of wipers (one for the driver's side, and one for the passenger side).
When you're setting up a wireless NIC to use an access point that requires encryption, and you read the encryption keys off of the WAP's configuration screen, do NOT put the string "s:" before the sequences because that means the keys are ASCII strings. You'll be getting hexadecimal values, so you don't want to treat them like strings, it messes everything up on the card.
If you're trying to repartition a hard drive where the partition table is hosed, i.e., one of the partitions extends past the physical end of the drive, try using the cfdisk utility with the -z option, which tells cfdisk to compose the partition table in memory and then impress the entire thing onto the hard drive without reading the (corrupt) partition table.
Make sure that the port you've connected to on the back of that Sun Microsystems machine really is the serial port.