查看CentOS版本

1. 查看核心版本

$ uname -or
$ uname -a

2. rpm

$ rpm --query centos-release  [On CentOS]
$ rpm --query redhat-release  [On RHEL]

3. hostnamectl 推荐

$ hostnamectl

4. file

$ cat /etc/centos-release    [On CentOS]
$ cat /etc/redhat-release    [On RHEL]
$ cat /etc/system-release
$ cat /etc/os-release         #contains more information