在 Ubuntu 中查詢、安裝特定版本的套件

想查詢在 Ubuntu 上特定的套件有哪個版本可以選擇時，可以利用 apt-cache 指令來查詢。

root@ubuntu:/home/ubuntu# apt-cache policy apache2
apache2:
  Installed: (none)
  Candidate: 2.4.7-1ubuntu4.1
  Version table:
     2.4.7-1ubuntu4.1 0
        500 http://nova.clouds.archive.ubuntu.com/ubuntu/ trusty-updates/main amd64 Packages
        500 http://security.ubuntu.com/ubuntu/ trusty-security/main amd64 Packages
     2.4.7-1ubuntu4 0
        500 http://nova.clouds.archive.ubuntu.com/ubuntu/ trusty/main amd64 Packages

然後在知道版本名稱後，需要安裝特定版本的套件時，就可以透過指定版本來達成。

apt-get install apache2=2.4.7-1ubuntu4

不過以 Ubuntu 14.04 來說，想要安裝 Apache2 的 2.4.7-lubuntu4 版本會出現以下的錯誤

Reading package lists... Done
Building dependency tree
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
 apache2 : Depends: apache2-bin (= 2.4.7-1ubuntu4) but 2.4.7-1ubuntu4.1 is to be installed
           Depends: apache2-data (= 2.4.7-1ubuntu4) but 2.4.7-1ubuntu4.1 is to be installed
           Recommends: ssl-cert but it is not going to be installed
E: Unable to correct problems, you have held broken packages.

就是說相關的套件也必須特別指定對應的版本，才有辦法正常地完成安裝
因此就 Apache2 這個例子來說，必須要針對 apache2、apache2-bin 和 apache2-data 三個套件都指定版本：

apt-get install apache2=2.4.7-1ubuntu4 apache2-bin=2.4.7-1ubuntu4 apache2-data=2.4.7-1ubuntu4

參考資料：
1、How can I check the available version of a package in the repositories?
2、How to install specific Ubuntu packages, with exact version?