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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"

write the output of a command to /var/log/user.log... each line will contain $USER, making this easy to grep for.
This command is useful if you want to copy the output of a series of commands to a file, for example if you want to pastebin the output from 'uname -a', 'lspci -vvv' and 'lsmod' for video driver trouble-shooting on your favorite Linux forum. 'log' takes all the following arguments as a command to execute, with STDOUT sent to /var/log/user.log. The command is echoed to the log before it is executed. The advantages of using logger (as opposed to appending output from commands to a file) are 1) commands are always appended to the logs... you don't have to worry about clobbering your log file accidentally by using '>' rather than '>>' 2) logs are automatically cleaned up by logrotate. The following functions allow you to mark the start and end of a section of /var/log/user.log. $ startlog() { export LOGMARK=$(date +%Y.%m.%d_%H:%M:%S); echo "$LOGMARK.START" | logger -t $USER; } then $ endlog() { echo "$LOGMARK.END" | logger -t $USER; } printlog will print all lines between $LOGMARK.START and $LOGMARK.END, removing everything that is prepended to each line by logger. $ printlog() { sudo sed -n -e "/$LOGMARK.START/,/$LOGMARK.END/p" /var/log/user.log| sed "s/.*$USER: //"; } The following command should dump just about all the information that you could possibly want about your linux configuration into the clipboard. $ startlog; for cmd in 'uname -a' 'cat /etc/issue' 'dmesg' 'lsusb' 'lspci' 'sudo lshw' 'lsmod'; do log $cmd; done; endlog; printlog | xsel --clipboard This is ready for a trip to http://pastebin.com/, and you don't have to worry about leaving temporary files lying around cluttering up $HOME. Caveats: I'm sure that startlog, endlog, and printlog could use some cleanup and error checking... there are unchecked dependencies between printlog and endlog, as well as between endlog and startlog. It might be useful for 'log' to send stderr to logger as well.

See udev at work
See how your system works with pendrives/mice/monitors/whatever-you-can-plug-in. Use cases: see on which /dev/... your peripherals are, find out if a specific udev rule is being applied correctly.

Find usb device
I often use it to find recently added ou removed device, or using find in /dev, or anything similar. Just run the command, plug the device, and wait to see him and only him

Copy stdin to your X11 buffer
Have you ever had to scp a file to your work machine in order to copy its contents to a mail? xclip can help you with that. It copies its stdin to the X11 buffer, so all you have to do is middle-click to paste the content of that looong file :)

Get AWS temporary credentials ready to export based on a MFA virtual appliance
You might want to secure your AWS operations requiring to use a MFA token. But then to use API or tools, you need to pass credentials generated with a MFA token. This commands asks you for the MFA code and retrieves these credentials using AWS Cli. To print the exports, you can use: `awk '{ print "export AWS_ACCESS_KEY_ID=\"" $1 "\"\n" "export AWS_SECRET_ACCESS_KEY=\"" $2 "\"\n" "export AWS_SESSION_TOKEN=\"" $3 "\"" }'` You must adapt the command line to include: * $MFA_IDis ARN of the virtual MFA or serial number of the physical one * TTL for the credentials

mplayer webcam window for screencasts
When recording screencast some people like to have the image from their webcam, so the can show something, that can't be seen on the desktop. So starting mplayer with these parameters you will have a window with no frames, borders whatsoever, and selecting the window a hitting the "F" key you will bring it in fullscreen. if you want to position the frame somewhere else, you could play with the --geomeptry option where 100%:100% mean bottom right corner. The HEIGHT and WIDTH can't be changed as you like, since the most webcams support specified dimensions, so you would have to play with it to see what is supported

Generate random valid mac addresses
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