查看centos系统版本的方法：

1、使用lsb_release -a命令查看

[root@centos6 ~]# lsb_release -a
LSB Version:    :base-4.0-amd64:base-4.0-noarch:core-4.0-amd64:core-4.0-noarch:graphics-4.0-amd64:graphics-4.0-noarch:printing-4.0-amd64:printing-4.0-noarch
Distributor ID:    CentOS
Description:    CentOS release 6.9 (Final)
Release:    6.9
Codename:    Final

但是，centos7.3里没有lsb_release命令。

2、使用cat /etc/os-release命令打开文件查看

[root@centos7 app]# cat /etc/os-release 
NAME="CentOS Linux"
VERSION="7 (Core)"
ID="centos"
ID_LIKE="rhel fedora"
VERSION_ID="7"
PRETTY_NAME="CentOS Linux 7 (Core)"
ANSI_COLOR="0;31"
CPE_NAME="cpe:/o:centos:centos:7"
HOME_URL="https://www.centos.org/"
BUG_REPORT_URL="https://bugs.centos.org/"

CENTOS_MANTISBT_PROJECT="CentOS-7"
CENTOS_MANTISBT_PROJECT_VERSION="7"
REDHAT_SUPPORT_PRODUCT="centos"
REDHAT_SUPPORT_PRODUCT_VERSION="7"

3、使用cat /etc/redhat-release（/etc/centos-release）命令查看

[root@centos6 ~]# cat /etc/redhat-release 
CentOS release 6.9 (Final)
[root@centos7 app]# cat /etc/redhat-release 
CentOS Linux release 7.3.1611 (Core)

4、使用rpm -q centos-release命令查看

[root@centos6 ~]# rpm -q centos-release
centos-release-6-9.el6.12.3.x86_64
[root@centos7 app]# rpm -q centos-release
centos-release-7-3.1611.el7.centos.x86_64