How to set up an SSH tunnel?
ssh -L [tunnel-in-port]:[client-host]:[tunnel-out-port] [user@host-to-reach]
Example:
ssh -L 13306:localhost:3306 user@server.org
It will forward all incoming data from localhost:13306 to server.org:3306.
Some web servers are only available through a gateway. To access it from your computer, you can also use a SSH tunnel:
ssh -L 8080:webserver:80 gw
How to search a pattern in a set of files
The best option is to use find to construct the set of files and then use grep.
find . -name Makefile | xargs grep pattern
List open ports
netstat -lnptu
Find big folders in a file system
du -hms /* | sort -nr | head
It will give the top ten of big folders sorted by size (in Mb) descending.
Find big files
find /-size +4000k -exec ls -lia {} \;
It will list files having a size > 4000k in /.
List installed packages
dpkg -l | grep '^ii'
Top 10 process using the most memory
ps aux --sort=-%mem | awk 'NR<=10{print $0}'