【yum】CentOS yum中$releasever、 $basearch等变量含义

如何获取 redhat 或 CentOS 发行版本号？

第一种方法，也是最容易想到的方法是查看 /etc/issue 和 /etc/redhat-release这两个文件，这两个文件都差不多，都含有发行号

第二种方法是使用命令，在RHEL 5 或 CentOS 5 中有个命令： lsb-release，通过这个命令可以查到，不过在RHEL 6就没这么幸运了，在我的最小化系统中找不到这个命令，看来此路又不通了。

不过有一个线索，那就是在CentOS自带的yum源文件中使用了 $releasever , $basearch等这些变量，奇怪的是这些变量的值是从哪获取的呢？

Google 一下之后，说明Yum变量的说明可以在这里（5.3.3. Using YumVariables）找到，说明如下：

Using Yum Variables

You can use and reference the following built-in variables inyum commands and in all Yum configuration files (that is,/etc/yum.conf and all .repo files in the /etc/yum.repos.d/directory):

$releasever

You can use this variable to reference the release version of Red Hat Enterprise Linux. Yum obtains the value of $releasever from the distroverpkg=value line in the /etc/yum.conf configuration file.

If there is no such linein /etc/yum.conf, then yum infers the correct value by deriving theversion number from the redhat-release package.

$arch

You can use this variable to refer to the system’s CPU architecture as returned when calling Python’s os.uname() function.Valid values for $arch include: i586, i686 and x86_64.

$basearch

You can use $basearch to reference the base architecture ofthe system.

For example, i686 and i586 machines both have a base architecture of i386, and AMD64 and Intel64 machines have a base architecture of x86_64.

$YUM0-9

These ten variables are each replaced with the value of anyshell environment variables with the same name.

If one of the sevariables is referenced (in /etc/yum.conf for example) and a shell environment variable with the same name does not exist, then the configuration file variable is not replaced.

To define a custom variable or to override the value of anexisting one, create a file with the same name as the variable(without the “$” sign) in the /etc/yum/vars/ directory, and add the desired value on its first line.

For example, repository descriptions often include the operating system name. To define a new variable called $osname,create a new file with “Red Hat Enterprise Linux” on the first lineand save it as /etc/yum/vars/osname:

# echo “Red Hat Enterprise Linux” >/etc/yum/vars/osname

Instead of “Red Hat Enterprise Linux 6”, you can now use the following in the .repo files:

name=$osname $releasever

文中说到$releasever的定义可以查看 /etc/yum.conf 文件的事distroverpkg=value行，打开 /etc/yum.conf 看一下

# cat /etc/yum.conf