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Linux is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds.

Common Operations

Check DNS of local computer
scutil --dns | grep 'nameserver\[[0-9]*\]'

Current OS Release version
cat /etc/*release

Check a Domain dscacheutil -q host -a name

Change Hostname

Ubuntu apt-get complains about unverifiable public key signature
sudo apt-key adv --keyserver --recv-keys <KEY>

Change SSH Key Password
ssh-keygen -p -f <keyfile> e.g. ssh-keygen -p -f ~/.ssh/id_rsa

Change file extension (from .old to .new) recursively inside a folder find ./ -depth -name "*.old" -exec sh -c 'mv "$1" "${1%.t1}.new"' _ {} \;