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Schedule a script or command in x num hours, silently run in the background even if logged out
This is helpful for shell scripts, I use it in my custom php install script to schedule to delete the build files in 3 hours, as the php install script is completely automated and is made to run slow. Does require at, which some environments without crontab still do have. You can add as many commands to the at you want. Here's how I delete them in case the script gets killed. (trapped) atq |awk '{print $1}'|xargs -iJ atrm J &>/dev/null

Which processes are listening on a specific port (e.g. port 80)
swap out "80" for your port of interest. Can use port number or named ports e.g. "http"

Check disk for bad sectors
Checks HDD for bad sectors, just like scandisk or chkdisk under some other operating system ;-).

ps a process keeping the header info so you know what the columns of numbers mean!
USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND root 1828 0.0 0.0 5396 476 ? Ss 2008 0:00 /usr/sbin/sshd

Query cheat.sh from the termianl. A quick access cheat sheet for a range of linux commands!

Print just line 4 from a textfile
Prints the 4th line and then quits. (Credit goes to flatcap in comments: http://www.commandlinefu.com/commands/view/6031/print-just-line-4-from-a-textfile#comment.)

Generate random valid mac addresses
Ruby version. Also, a perl version: $perl -e 'printf("%.2x.",rand(255))for(1..5);printf("%.2x\n",rand(255))'

Change prompt to MS-DOS one (joke)
This one eliminates the additional backslash at the end (which is not necessary)

Short and elegant way to backup a single file before you change it.
Remember to backup everything before changing it so you can restore all to normal.

Mirror a directory structure from websites with an Apache-generated file indexes
wget/curl/friends are not good with mirroring files off websites, especially those with Apache-generated directory listings. These tools endlessly waste time downloading useless index HTML pages. lftp's mirror command does a better job without the mess.


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