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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"

Detect illegal access to kernel space, potentially useful for Meltdown detection
Based on capsule8 agent examples, not rigorously tested

Efficiently extract lines between markers
GNU Sed can 'address' between two regex, but it continues parsing through to the end of the file. This slight alteration causes it to terminate reading the input file once the STOP match is made. In my example I have included an extra '/START/d' as my 'start' marker line contains the 'stop' string (I'm extracting data between 'resets' and using the time stamp as the 'start'). My previous coding using grep is slightly faster near the end of the file, but overall (extracting all the reset cycles in turn) the new SED method is quicker and a lot neater.

Find usb device in realtime
Using this command you can track a moment when usb device was attached.

Create a mirror of a local folder, on a remote server
Create a exact mirror of the local folder "/root/files", on remote server 'remote_server' using SSH command (listening on port 22) (all files & folders on destination server/folder will be deleted)

See system users

Look at your data as a greymap image.
Keep width to a power of 2 to see patterns emerge. 512 is good. So is 4096 for huge maps. PNM headers are super basic. http://netpbm.sourceforge.net/doc/pbm.html

Get fully qualified domain names (FQDNs) for IP address with failure and multiple detection

Delete recursively only empty folders on present dir

Discovering all open files/dirs underneath a directory
It may be helpful in case you need to umount a directory and some process is preventing you to do so keeping the folder busy. The lsof may process the +D option slowly and may require a significant amount of memory because it will descend the full dir tree. On the other hand it will neither follow symlinks nor other file systems.


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