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Getting started with tcpdump
At some point you want to know what packets are flowing on your network. Use tcpdump for this. The man page is obtuse, to say the least, so here are some simple commands to get you started. -n means show IP numbers and don't try to translate them to names. -l means write a line as soon as it is ready. -i eth0 means trace the packets flowing through the first ethernet interface. src or dst w.x.y.z traces only packets going to or from IP address w.x.y.z. port 80 traces only packets for HTTP. proto udp traces only packets for UDP protocol. Once you are happy with each option combine them with 'and' 'or' 'not' to get the effects you want.

check open ports without netstat or lsof

Adding Prefix to File name

Record output of any command using 'tee' at backend; mainly can be used to capture the output of ssh from client side while connecting to a server.
Optionally, you can create a new function to do this with a custom command. Edit $HOME/.bashrc and add: myssh () { ssh $1 | tee sshlog ; } Save it. At command prompt: $ myssh user@server

Copy an element from the previous command
'n' is a non-negative integer. Using 0 will expand to the name of the previous command.

List installed deb packages by size

Download all data from Google Ngram Viewer
To learn more about Google Ngram Viewer: http://ngrams.googlelabs.com/info

send kernel log (dmesg) notifications to root via cron
this is helpful because dmesg is where i/o errors, etc are logged to... you will also be able to see when the system reboots or someone attaches a thumb drive, etc. don't forget to set yourself up in /etc/aliases to get roots email.

Kill all processes belonging to a user

matrix in your term
-a : Asynchronous scroll -b : Bold characters on -x : X window mode, use if your xterm is using mtx.pcf


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