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Clean apt-get and gpg cache and keys
Cleans apt-get and gpg cache and keys

Record camera's output to a avi file
video.avi is the resulting file. Press Ctrl+c to stop the recording. You can change the OVC option to another to record into a different format.

vmstat/iostat with timestamp
Also useful with iostat, or pretty much anything else you want timestamped.

Archive all files that have not been modified in the last days
Finally, we can make the file "unchangeable" sudo chattr +i

Change the From: address on the fly for email sent from the command-line
It's very common to have cron jobs that send emails as their output, but the From: address is whatever account the cron job is running under, which is often not the address you want replies to go to. Here's a way to change the From: address right on the command line. What's happening here is that the "--" separates the options to the mail client from options for the sendmail backend. So the -f and -F get passed through to sendmail and interpreted there. This works on even on a system where postfix is the active mailer - looks like postfix supports the same options. I think it's possible to customize the From: address using mutt as a command line mailer also, but most servers don't have mutt preinstalled.

Remove blank lines from a file using grep and save output to new file
The ^$ within the quotes is a regular expression: ^=beginning of line, $=end of line, with no characters between.

Transform a portrait pdf in a landscape one with 2 pages per page
This is an example of the usage of pdfnup (you can find it in the 'pdfjam' package). With this command you can save ink/toner and paper (and thus trees!) when you print a pdf. This tools are very configurable, and you can make also 2x2, 3x2, 2x3 layouts, and more (the limit is your fantasy and the resolution of the printer :-) You must have installed pdfjam, pdflatex, and the LaTeX pdfpages package in your box.

Set laptop display brightness
An alternative which does not require to be root

Remotely sniff traffic and pass to snort
I have a small embedded linux device that I wanted to use for sniffing my external network, but I didn't want to recompile/cross-compile snort for the embedded platform. So I used tcpdump over ssh to pass all the traffic as pcap data to a "normal" Linux system that then takes the pcap data and passes it to snort for processing.

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"


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