Install preparations

1. Ubuntu:

apt-get install openssl cron  netcat-openbsd  curl

Or install netcat.

apt-get install netcat

2. CentOS

yum -q -y install  openssl  crontabs  netcat-openbsd curl

For centos 5:

yum -q -y install openssl vixie-cron netcat-openbsd curl

Or install nc

yum -q -y install nc

3. alpine

The default nc tool doesn't support -4 , -6 and local address, So, please install netcat-openbsd to support all the options.

apk --no-cache add -f openssl curl netcat-openbsd