Check whether the current operating system is ubuntu or centos

Check whether the current operating system is ubuntu or centos

1. Execute: lsb_release -a

2. Command: cat /etc/redhat-release

3. Command:  cat /etc/issue

Summary: In fact, it is to see if there is a certain file:

radhat or centos exists: /etc/redhat-release this file [command cat /etc/redhat-release ]
ubuntu exists: /etc/lsb-release this file [command cat /etc/lsb-release ]

The following two systems have not been used in practice.

Debian exists cat /etc/debian_version this file
Slackware exists cat /etc/slackware_version this file