iredmail安装脚本分析（三）---conf/global DISTRO值的来源及操作系统的判断

作者在引入conf/global 文件时，就已经对操作系统的类型进行判断，同时也对DISTRO进行了赋值。

部分代码，如图：

显然文件里的KERNEL_NAME的值就是判断完成的操作系统，具体分析该值是如何得到的。

就是通过命令“uname –s  | tr ‘[a-z]’ ‘[A-Z]’得到的，不过作者在此处把小写换成了大写。 接下来分析根据不同操作系统，怎么获得不同的DISTRO值，代码如下：

if [ X"${KERNEL_NAME}" == X'LINUX' ]; then
    # Directory of RC scripts.
    export DIR_RC_SCRIPTS='/etc/init.d'

    if [ -f /etc/redhat-release ]; then
        # RHEL/CentOS
        export DISTRO='RHEL'

        # Get distribution version
        if grep '\ 6' /etc/redhat-release &>/dev/null; then
            # version .x
            export DISTRO_VERSION=''
        elif grep '\ 7' /etc/redhat-release &>/dev/null; then
            # version .x
            export DISTRO_VERSION=''
        else
            export UNSUPPORTED_RELEASE='YES'
        fi

        # Get distribution name as DISTRO_CODENAME
        if grep '^Red' /etc/redhat-release &>/dev/null; then
            # RHEL
            export DISTRO_CODENAME='rhel'
        elif grep '^CentOS' /etc/redhat-release &>/dev/null; then
            # CentOS
            export DISTRO_CODENAME='centos'
        elif grep '^Scientific' /etc/redhat-release &>/dev/null; then
            # Scientific Linux
            export DISTRO_CODENAME='scientific'
        else
            export UNSUPPORTED_RELEASE='YES'
        fi

    elif [ -f /etc/lsb-release ]; then
        # Ubuntu
        export DISTRO='UBUNTU'

        # Ubuntu version number and code name:
        #   - 14.04: trusty
        #   - 15.04: vivid
        export DISTRO_ID="$(grep 'DISTRIB_ID' /etc/lsb-release | awk -F'=' '{print $2}')"
        export DISTRO_VERSION="$(grep 'DISTRIB_RELEASE' /etc/lsb-release | awk -F'=' '{print $2}')"
        export DISTRO_CODENAME="$(grep 'DISTRIB_CODENAME' /etc/lsb-release | awk -F'=' '{print $2}')"

        # Unsupported releases: .x, .x, 14.10
        if echo "${DISTRO_VERSION}" | grep -E '^(12|13|14\.10)' &>/dev/null ; then
            export UNSUPPORTED_RELEASE='YES'
        fi
    elif [ -f /etc/debian_version ]; then
        # Debian
        export DISTRO='DEBIAN'

        # Get major release version number
        export DISTRO_VERSION="$(cat /etc/debian_version)"

        # Set distro code name and unsupported releases.
        if grep '^7' /etc/debian_version &>/dev/null || \
            grep -i '^wheezy' /etc/debian_version &>/dev/null; then
            export DISTRO_VERSION=''
            export DISTRO_CODENAME='wheezy'
        elif grep '^8' /etc/debian_version &>/dev/null || \
            grep -i '^jessie' /etc/debian_version &>/dev/null; then
            export DISTRO_VERSION=''
            export DISTRO_CODENAME='jessie'
        else
            export UNSUPPORTED_RELEASE='YES'
        fi

        # Override settings.
        export SHELL_NOLOGIN='/usr/sbin/nologin'
    else
        export UNSUPPORTED_RELEASE='YES'
    fi
elif [ X"${KERNEL_NAME}" == X'FREEBSD' ]; then
    export DISTRO='FREEBSD'
    export DISTRO_VERSION="$(uname -r |awk -F'[.-]' '{print $1}')"

    # Directory of RC scripts.
    export DIR_RC_SCRIPTS='/usr/local/etc/rc.d'
    export PYTHON_BIN='/usr/local/bin/python'

    # Unsupported releases: , .
    if echo "${DISTRO_VERSION}" | grep '^[78]' &>/dev/null ; then
        export UNSUPPORTED_RELEASE='YES'
    fi

    export SHELL_BASH='/usr/local/bin/bash'

    # Default password scheme.
    export DEFAULT_PASSWORD_SCHEME='BCRYPT'

elif [ X"${KERNEL_NAME}" == X'OPENBSD' ]; then
    export DISTRO='OPENBSD'
    export DISTRO_VERSION="$(uname -r)"

    # Directory of RC scripts.
    export DIR_RC_SCRIPTS='/etc/rc.d'
    export RC_CONF_LOCAL='/etc/rc.conf.local'
    export SHELL_BASH='/usr/local/bin/bash'
    export PYTHON_BIN='/usr/local/bin/python'

    # Unsupported release: 5.6 and earlier versions.
    if echo "${DISTRO_VERSION}" | grep '^5.[123456]' &>/dev/null ; then
        export UNSUPPORTED_RELEASE='YES'
    fi

    # Default password scheme.
    export DEFAULT_PASSWORD_SCHEME='BCRYPT'

else
    # Not support *BSD and other distrobutions yet.
    echo "Error: Your OS is not supported yet."
    exit
fi

代码比较长，不过脉络比较清晰，首先根据KERNEL_NAME的值判断是哪种操作系统，作者给出的判断是3种，分别是LINUX   OPENBSD   FREEBSD  , 也就是该脚本只能在这3种平台上进行部署，如果需要自己扩展的话，就可以在增加新的判断，最后如果3种都不是的话，就直接返回255，如下代码:

echo "Error: Your OS is not supported yet."
exit 

接下来分析当KERNEL_NAME的值为LINUX，脚本做了什么，首先定义了一个变量

export DIR_RC_SCRIPTS='/etc/init.d'

linux中一般启动脚本都是放在这个目录里的,LINUX本身也有很多版本，因此作者在此处又进行多种类型的判断，判断的依据文件分别是/etc/redhat-release  /etc/lsb-release  /etc/debian_version这3种文件分别对应rhel/centos  ubuntu  debian  , 从而也说明在LINUX的版本中，只支持这3种，其他的LINUX版本是不支持的，最后作者返回一句代码：

定义了一个UNSUPPORTED_RELEASE变量，在后续的代码应该会调用这个变量来判断是否支持。

针对这3种LINUX，作者又具体细分到不同的小版本中，首先看rhel/centos 系列，下面代码：

首先根据存在redhat-release文件，定义了DISTRO的值

if [ -f /etc/redhat-release ]; then

export DISTRO='RHEL'

这样在get_all.sh的脚本里调用时就有了判断依据，接着判断具体的版本，

if grep '\ 6' /etc/redhat-release &>/dev/null; then
            # version .x
            export DISTRO_VERSION=''
        elif grep '\ 7' /etc/redhat-release &>/dev/null; then
            # version .x
            export DISTRO_VERSION=''
        else
            export UNSUPPORTED_RELEASE='YES'
        fi

显然只支持6和7两个版本，也就是安装时，如果不是这2个版本的话，就会返回unsupport_release的值为YES了。

rhel还有两个个反编译版本即centos ，Scientific Linux,    因此作者又定义了一个变量来区别 DISTRO_CODENAME, 代码如下:

if grep '^Red' /etc/redhat-release &>/dev/null; then
            # RHEL
            export DISTRO_CODENAME='rhel'
        elif grep '^CentOS' /etc/redhat-release &>/dev/null; then
            # CentOS
            export DISTRO_CODENAME='centos'
        elif grep '^Scientific' /etc/redhat-release &>/dev/null; then
            # Scientific Linux
            export DISTRO_CODENAME='scientific'
        else
            export UNSUPPORTED_RELEASE='YES'
        fi

显然在/etc/redhat-release文件里，不同的发行版本有不同的关键字，这样关于红帽系的操作系统，作者就已经区分完毕了。

---

接下来关于ubuntu的判断就简单多了，看图

根据/etc/lsb-release的文件是否存在，赋值DISTRO为UBUNTU，然后判断具体版本，看代码

        export DISTRO_ID="$(grep 'DISTRIB_ID' /etc/lsb-release | awk -F'=' '{print $2}')"
        export DISTRO_VERSION="$(grep 'DISTRIB_RELEASE' /etc/lsb-release | awk -F'=' '{print $2}')"
        export DISTRO_CODENAME="$(grep 'DISTRIB_CODENAME' /etc/lsb-release | awk -F'=' '{print $2}')"

        # Unsupported releases: .x, .x, 14.10
        if echo "${DISTRO_VERSION}" | grep -E '^(12|13|14\.10)' &>/dev/null ; then
            export UNSUPPORTED_RELEASE='YES'
        fi

从程序可以看出UBUNTU的ID ,  RELEASE ,  CODENAME的值都在/etc/lsb-release的文件里，用grep 和awk匹配后，赋予不同变量的值。

用grep 筛选出系统版本为12,13,14.10的都为不支持版本，目前支持的版本为14.04,15.04

---

接下来判断的就是DEBIAN了，同样是判断文件，如图：

文件存在，则DISTRO的值为DEBIAN，接下来判断版本号：

# Get major release version number
        export DISTRO_VERSION="$(cat /etc/debian_version)"

cat /etc/debian_version  一个命令就可以得到具体版本，比rhel更容易判断

接下来对具体版本进行判断，见代码：

# Set distro code name and unsupported releases.
        if grep '^7' /etc/debian_version &>/dev/null || \
            grep -i '^wheezy' /etc/debian_version &>/dev/null; then
            export DISTRO_VERSION=''
            export DISTRO_CODENAME='wheezy'
        elif grep '^8' /etc/debian_version &>/dev/null || \
            grep -i '^jessie' /etc/debian_version &>/dev/null; then
            export DISTRO_VERSION=''
            export DISTRO_CODENAME='jessie'
        else
            export UNSUPPORTED_RELEASE='YES'
        fi

显然只支持DEBIAN的7,8两个版本，到此DISTRO的值和操作系统的判断结束，如果想新增特殊操作系统的话或者自己定义的话，在此处加入自己的代码即可。