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# render template via ansible module
$ ansible all -i "localhost," \
              -c local \
              -m template \
              -a "src=test.txt.j2 dest=./test.txt" \
              --extra-vars='{"users": ["Mike", "Smith", "Klara", "Alex"]}'

# render template via playbook
- hosts: 127.0.0.1
  tasks:

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# create virtual env
pyenv virtualenv <py version> <env name>

pyenv activate <env name>
pyenv deactivate

# list virtual env
pyenv virtualenvs

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# compress file into gzip 
tar --create --gzip --verbose --file <output file path> <input file path>
tar -czvf <output file path> <input file path>

# extract 
tar -xzvf <file path>

# gzip option can be changed to use different compression algo
# https://www.howtogeek.com/248780/how-to-compress-and-extract-files-using-the-tar-command-on-linux/

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<file glob> {

}

# run logrotate 
logrotate --verbose --debug --force <logroate file | logrotate.d/>

# logrotate status
# check for past logrotate actions
/var/lib/logrotate.status

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# encrypt
openssl aes-256-cbc -in <file> -out <file> -md sha1 -base64

# decrypt
openssl aes-256-cbc -d -in <file> -out <file> -md sha1 -base64

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ssh-keygen -E md5 -lf id_rsa.pub

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# self-signed certificates only provide cryptographic security to HTTPS request
# they do not verify the identity of the server
sudo openssl req -x509 -nodes -newkey rsa:4096 \
-keyout /etc/ssl/<name>.key \
-out /etc/ssl/<name>.crt \
-days <NUMBER_OF_DAYS>

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[Unit]
StartLimitIntervalSec=60 #length of limit interval
StartLimitBurst=6 #start limit within interval
# i.e. can start 6 times in a span of 60 sec
ConditionPathExists=/etc/foo/foo.conf # only start if this file exists
# see other Condition* directives

[Service]
RestartSec=10 # restart every 10 if restart conditions are met

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sudo du -Sh | sort -r -h | head -n 100

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# mac
sed 's/<target>/<replacement>/g' <inputfile> > <outputfile>

# inplace
sed -i '.bck' 's/<target>/<replacement>/g' <inputfile>

# only if FOO appears in the line
sed 'FOO/s/<target>/<replacement>/g' <inputfile>

# multiple command