Startup key combinations for Intel-based Macs

KeystrokeDescriptionPress C during startupStart up from a bootable CD or DVD, such as the Mac OS X Install disc that came with the computer.Press D during startupStart up in Apple Hardware Test (AHT).Press Option-Command-P-R until you hear two beeps.Reset NVRAMPress Option during startupStarts into Startup Manager, where you can select a Mac OS X volume to start from. Note: Press N to make the the first bootable Network volume appear as well.Press Eject, F12, or hold the mouse or trackpad buttonEjects any removable media, such as an optical disc.Press N during startupAttempt to start up from a compatible network server (NetBoot).Press T during startupStart up in Target Disk Mode.Press Shift during startupStart up in Safe Boot mode and temporarily disable login items.Press Command-V during startupStart up in Verbose mode.Press Command-S during startupStart up in Single-User mode.Press Option-N during startupStart from a NetBoot server using the default boot image.

How to Kill User Session in Linux

This command will be useful if in case your user is doing something “naughty” and you want to kill them this is how you do it:

How to stop and halt (pause) the user

# skill -STOP -u username

How to continue the halted user

# skill -CONT -u username

How to Kill and make them logout from the computer

# skill -KILL -u username

How to kill all the user in the system

# skill -KILL -v /dev/pts/*

Hope this will be useful for some of you to who have some difficult time with the user.