因为UNIX是The Open Group拥有的商标(Trade Mark)。 凡是在一定程度上遵守POSIX规范， 但是没有被授权使用UNIX商标的操作系统不能称为UNIX，只能称为Unix-like。

Unix-like
├── MINIX
├── BSD-based
│   ├── OpenBSD
│   ├── FreeBSD
│   └── NetBSD
├── GNU/Hurd
│   └── Debian GNU/Hurd
└── GNU/Linux
    ├── Debian GNU/Linux
    ├── Ubuntu
    ├── CentOS
    └── ...

• MINIX
• BSD-based
• GNU/Hurd
• GNU/Linux

Unix-like系统相对比较自由，有时候，我们需要判别是哪个操作系统，分别做不同的操作。

判别的bash脚本如下：

if [ -f "/etc/alpine-release" ] ; then
    echo "your os is AlpineLinux"
elif [ -f "/etc/debian_version" ] ; then
    echo "your os is Debian"
elif [ -f "/etc/lsb-release" ] ; then
    echo "your os is Ubuntu"
elif [ -f "/etc/fedora-release" ] ; then
    echo "your os is Fedora"
elif [ -f "/etc/centos-release" ] ; then
    echo "your os is CentOS"
elif [ -f "/etc/redhat-release" ] ; then
    echo "your os is RHEL"
else
    echo "your os is not recognized!"
fi

参考

systemd初始化系统提供了一个统一的配置文件/etc/os-release。

使用systemd作为初始化系统的操作系统有如下：

判别的bash脚本如下：

local id=`grep "^ID=" /etc/os-release | awk -F= '{print $2}'`
if [ "$id" == "alpine" ] ; then
    echo "your os is AlpineLinux"
elif [ "$id" == "debian" ] ; then
    echo "your os is Debian"
elif [ "$id" == "ubuntu" ] ; then
    echo "your os is Ubuntu"
elif [ "$id" == "fedora" ] ; then
    echo "your os is Fedora"
elif [ "$id" == "\"centos\"" ] ; then
    echo "your os is CentOS"
elif [ "$id" == "redhat" ] ; then
    echo "your os is RHEL"
else
    echo "your os is not recognized!"
fi