Yum中$releasever和$basearch的取值

查看/etc/yum.repos.d/CentOS-Base.repo

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[base]
name=CentOS-$releasever - Base
mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=os&infra=$infra
#baseurl=http://mirror.centos.org/centos/$releasever/os/$basearch/
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-6

其实在日常使用之中,我们在很多地方,特别是脚本内看到了调用$releasever$basearch

  1. $releasever的值,这个表示当前系统的发行版本
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[root@ultraera /]# rpm -qi centos-release
Name : centos-release Relocations: (not relocatable)
Version : 6 Vendor: CentOS
Release : 7.el6.centos.12.3 Build Date: Tue 04 Aug 2015 12:13:46 AM CST
Install Date: Sat 21 May 2016 03:31:27 AM CST Build Host: c6b9.bsys.dev.centos.org
Group : System Environment/Base Source RPM: centos-release-6-7.el6.centos.12.3.src.rpm
Size : 35634 License: GPLv2
Signature : RSA/SHA1, Tue 04 Aug 2015 12:15:08 AM CST, Key ID 0946fca2c105b9de
Packager : CentOS BuildSystem <http://bugs.centos.org>
Summary : CentOS release file
Description :
CentOS release files

# 其中Version 6 就是我们的版本号
  1. $basearch是我们的系统硬件架构(CPU指令集),就是我们常说的i386\i486\i586\i686\
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[root@ultraera /]# arch
i386

但是,当我在命令行查看是却发现$releasever$basearch是空的。


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

5.3.3. Using Yum Variables

You can use and reference the following built-in variables in yum 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 line in /etc/yum.conf, then yum infers the correct value by deriving the version 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 of the 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 any shell environment variables with the same name. If one of these variables 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 an existing 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 line and 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,默认文件(我的是CentOS 6)内容如下:

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[main]
cachedir=/var/cache/yum/$basearch/$releasever
keepcache=0
debuglevel=2
logfile=/var/log/yum.log
exactarch=1
obsoletes=1
gpgcheck=1
plugins=1
installonly_limit=5
bugtracker_url=http://bugs.centos.org/set_project.php?project_id=16&ref=http://bugs.centos.org/bug_report_page.php?category=yum
distroverpkg=centos-release

distroverpkg=centos-release 代表什么? 去哪找 centos-release 。找到这里我再一次表示困惑。
不过另一篇文章进行了我的视野: yum的$releasever真是太反动了, 关键内空如下:

在 /etc/yum.repos.d/ 目录下的软件库定义文件中,常常会在 baseurl 的路径中提到 $releasever 这个变量,表示当前发行版的大版本号,但大家知道这个变量是在哪设置的吗?我 grep 了整个 etc 目录都没找到,还是看了 yum.conf 才知道的,是在 yum.conf 文件里 distroverpkg 选项定义的。但这个选项就很有问题:

distroverpkg 和 releasever 名字不同,且看不出什么联系
distroverpkg 的值,并不是明文,而是“redhat-release”。不知道大家看到这个会有什么想法,反正我是首先想到了 /etc/redhat-release 文件,但我错了。实际上指的是 redhat-release 这个RPM包。所谓“distroverpkg=redhat-release”的意思,其实是将 $releasever 设置为 redhat-release 这个RPM包的版本号.

小结:

yum中的$releasever变量是取redhat-release-server rpm包的属性值( %{version})。
[root@ldap01 ~]# rpm -q –qf %{version} redhat-release-server;echo
6Server

# Yum
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