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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"

Show which process is blocking umount (Device or resource is busy)
Instead of using force un-mounting, it's better to find the processes that currently use the relevant folder. Taken from: http://www.linuxhowtos.org/Tips%20and%20Tricks/findprocesses.htm

Remove all unused kernels with apt-get
Remove old kernels (*-generic and *-generic-pae) via apt-get on debian/ubuntu based systems. Tested on ubuntu 10.04 - 12.04.

Print IP of any interface. Useful for scripts.

Determine next available UID
better with accounts on ldap

connect via ssh using mac address
Connect to a machine running ssh using mac address by using the "arp" command

See where a shortened url takes you before click

Benchmark SQL Query
Benchmark a SQL query against MySQL Server. The example runs the query 10 times, and you get the average runtime in the output. To ensure that the query does not get cached, use `RESET QUERY CACHE;` on top in the query file.

Connect to TCP port 5000, transfer data and close connexion.
With no '-q 0' switch, nc simply waits, and whatever awaits the data hangs.

Easy and fast access to often executed commands that are very long and complex.
When using reverse-i-search you have to type some part of the command that you want to retrieve. However, if the command is very complex it might be difficult to recall the parts that will uniquely identify this command. Using the above trick it's possible to label your commands and access them easily by pressing ^R and typing the label (should be short and descriptive). UPDATE: One might suggest using aliases. But in that case it would be difficult to change some parts of the command (such as options, file/directory names, etc).


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