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add repeated watermark to image

run a command from within vi without exiting
":! ls -l " results in listing the files in the current directory. pressing "enter" will get you back into vi.

Top 20 commands in your bash history

rename a file to its md5sum

Port Knocking!
Knock on ports to open a port to a service (ssh for example) and knock again to close the port. You have to install knockd. See example config file below. [options] logfile = /var/log/knockd.log [openSSH] sequence = 3000,4000,5000 seq_timeout = 5 command = /sbin/iptables -A INPUT -i eth0 -s %IP% -p tcp --dport 22 -j ACCEPT tcpflags = syn [closeSSH] sequence = 5000,4000,3000 seq_timeout = 5 command = /sbin/iptables -D INPUT -i eth0 -s %IP% -p tcp --dport 22 -j ACCEPT tcpflags = syn

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"

Resume an emerge, and keep all object files that are already built
For Gentoo: If you do not use this command, portage will fetch the source again, and rebuild the hole application from the top. This command make portage keep all files that ar allready built

Geolocate a given IP address
GeoIP Needs to be installed. Can be done from some distro's or via MaxMind.com for free. There even is a free city database availabble. If the GeoLiteCity is downloaded and installed it will also find more information $ geoiplookup -f /var/lib/GeoIP/GeoLiteCity.dat commandlinefu.com GeoIP City Edition, Rev 1: US, NJ, Absecon, 08201, 39.420898, -74.497704, 504, 609

Install an mpkg from the command line on OSX
Installing most OSX apps is just a matter of dropping it in /Applications, either GUI-wise or with cp -r. However, many packages are distributed in "mpkg" format, and those have to be installed with an installer. If you don't want to go to the trouble of firing up VNC to install an mpkg, you can use the "installer" command. This will install an application from a .mpkg it to /Applications system-wide. To install a program for just one user, replace "-target /" with "-target username".

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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