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clean up memory of unnecessary things (Kernerl 2.6.16 or newer)
run sync first to flush useful things out to disk!!! To free pagecache: echo 1 > /proc/sys/vm/drop_caches To free dentries and inodes: echo 2 > /proc/sys/vm/drop_caches To free pagecache, dentries and inodes: echo 3 > /proc/sys/vm/drop_caches

Determine status of a RAID write-intent bitmap
Report information about a bitmap file.

convert Decimal to IP from stdin
https://stackoverflow.com/questions/10768160/ip-address-converter

Salvage a borked terminal
This works in some situations where 'reset' and the other alternatives don't.

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).

List open sockets protocol/address/port/state/PID/program name

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)

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"

list all opened ports on host

Compare two CSV files, discarding any repeated lines
The value for the sort command's -k argument is the column in the CSV file to sort on. In this example, it sorts on the second column. You must use some form of the sort command in order for uniq to work properly.


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