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back ssh from firewalled hosts
host B (you) redirects a modem port (62220) to his local ssh. host A is a remote machine (the ones that issues the ssh cmd). once connected port 5497 is in listening mode on host B. host B just do a ssh 127.0.0.1 -p 5497 -l user and reaches the remote host'ssh. This can be used also for vnc and so on.

Print just line 4 from a textfile
this method should be the fastest

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"

this toggles mute on the Master channel of an alsa soundcard

Show drive names next to their full serial number (and disk info)
As of this writing, this requires a fairly recent version of util-linux, but is much simpler than the previous alternatives. Basically, lsblk gives a nice, human readable interface to all the blkid stuff. (Of course, I wouldn't recommend this if you're going to be parsing the output.) This command takes all the fun out of the previous nifty pipelines, but I felt I ought to at least mention it as an alternative since it is the most practical.

Calculate pi to an arbitrary number of decimal places
Change the scale to adjust number of decimal places prefix the command with "time" to benchmark the computer (compare how long it takes to calculate 10000 digits of pi on various computers).

Polkit: Force KDE apps to always recognize your display
KDE apps expect certain variables to be set, and unfortunately pkexec doesn’t set them by default. So, by setting this alias, it becomes possible to run, e.g. “pkexec kate” or “pkexec dolphin” and it’ll actually run.

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Change tha mac adresse
eth0 = the name of the interface 00:01:02:03:04:05 = the new mac adresse the same thing for wireless card $ sudo iwconfig eth1 hw ether 00:01:02:03:04:05

List of reverse DNS records for a subnet
This command uses nmap to perform reverse DNS lookups on a subnet. It produces a list of IP addresses with the corresponding PTR record for a given subnet. You can enter the subnet in CDIR notation (i.e. /24 for a Class C)). You could add "--dns-servers x.x.x.x" after the "-sL" if you need the lookups to be performed on a specific DNS server. On some installations nmap needs sudo I believe. Also I hope awk is standard on most distros.


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