【問題背景】
卸載安裝的Ambari，之前都是因為卸載不干凈。這次重寫安裝，卸載完之后，發現httpd無法啟動，所以想卸載httpd進行重新安裝，但是執行命令yum list | grep httpd報錯。
【遇到的問題】
配置過程很簡單，去https://opsx.alibaba.com/mirror 獲得執行命令：
但是我在執行yum makecache時報錯，報錯信息如下：
Loaded plugins: fastestmirror, langpacks, priorities Repository epel is listed more than once in the configuration Cleaning repos: base epel extras updates Cleaning up everything Maybe you want: rm -rf /var/cache/yum, to also free up space taken by orphaned data from disabled or removed repos Cleaning up list of fastest mirrors [root@hadoop01 yum.repos.d]# yum makecache Loaded plugins: fastestmirror, langpacks, priorities Repository epel is listed more than once in the configuration Determining fastest mirrors * base: mirrors.aliyun.com * extras: mirrors.aliyun.com * updates: mirrors.aliyun.com http://mirrors.aliyun.com/centos/%24releasever/os/x86_64/repodata/repomd.xml: [Errno 14] HTTP Error 404 - Not Found Trying other mirror. To address this issue please refer to the below wiki article https://wiki.centos.org/yum-errors If above article doesn't help to resolve this issue please use https://bugs.centos.org/. http://mirrors.aliyuncs.com/centos/%24releasever/os/x86_64/repodata/repomd.xml: [Errno 12] Timeout on http://mirrors.aliyuncs.com/centos/$releasever/os/x86_64/repodata/repomd.xml: (28, 'Connection timed out after 30000 milliseconds') Trying other mirror. http://mirrors.cloud.aliyuncs.com/centos/%24releasever/os/x86_64/repodata/repomd.xml: [Errno 14] curl#6 - "Could not resolve host: mirrors.cloud.aliyuncs.com; Unknown error" Trying other mirror. http://mirrors.aliyuncs.com/centos/%24releasever/os/x86_64/repodata/repomd.xml: [Errno 12] Timeout on http://mirrors.aliyuncs.com/centos/$releasever/os/x86_64/repodata/repomd.xml: (28, 'Connection timed out after 30001 milliseconds') Trying other mirror. http://mirrors.aliyuncs.com/centos/%24releasever/os/x86_64/repodata/repomd.xml: [Errno 12] Timeout on http://mirrors.aliyuncs.com/centos/$releasever/os/x86_64/repodata/repomd.xml: (28, 'Connection timed out after 30001 milliseconds') Trying other mirror. http://mirrors.aliyuncs.com/centos/%24releasever/os/x86_64/repodata/repomd.xml: [Errno 12] Timeout on http://mirrors.aliyuncs.com/centos/$releasever/os/x86_64/repodata/repomd.xml: (28, 'Connection timed out after 30001 milliseconds') Trying other mirror. http://mirrors.aliyuncs.com/centos/%24releasever/os/x86_64/repodata/repomd.xml: [Errno 12] Timeout on http://mirrors.aliyuncs.com/centos/$releasever/os/x86_64/repodata/repomd.xml: (28, 'Connection timed out after 30001 milliseconds') Trying other mirror. http://mirrors.aliyuncs.com/centos/%24releasever/os/x86_64/repodata/repomd.xml: [Errno 12] Timeout on http://mirrors.aliyuncs.com/centos/$releasever/os/x86_64/repodata/repomd.xml: (28, 'Connection timed out after 30001 milliseconds') Trying other mirror. ...
【解決方法】
在網上找了好多帖子，都沒能解決我的問題，后來看到是HTTP請求失敗，嘗試本地訪問之前wget下來的 CentOS-Base.repo 發現其中的：
http://mirrors.aliyun.com/centos/$releasever/os/$basearch/
等URL通過http的形式根本無法訪問，此時將變量$releasever改為7（我的系統是centos 7），發現可以訪問了，順便將所有的變量$releasever都改為7。感覺這個變量$releasever根本就沒起作用呀。
改完之后，執行yum clean all 以及 yum makecache 成功。
oaded plugins: fastestmirror, langpacks Determining fastest mirrors * base: mirrors.aliyun.com * extras: mirrors.aliyun.com * updates: mirrors.aliyun.com base | 3.6 kB 00:00:00 extras | 3.4 kB 00:00:00 updates | 3.4 kB 00:00:00 (1/12): base/x86_64/group_gz | 166 kB 00:00:00 (2/12): base/x86_64/primary_db | 6.0 MB 00:00:00 (3/12): base/x86_64/filelists_db | 7.1 MB 00:00:00 (4/12): base/x86_64/other_db | 2.6 MB 00:00:00 (5/12): extras/x86_64/prestodelta | 73 kB 00:00:00 (6/12): extras/x86_64/primary_db | 215 kB 00:00:00 (7/12): extras/x86_64/other_db | 131 kB 00:00:00 (8/12): extras/x86_64/filelists_db | 249 kB 00:00:00 (9/12): updates/x86_64/prestodelta | 945 kB 00:00:00 (10/12): updates/x86_64/filelists_db | 5.2 MB 00:00:00 (11/12): updates/x86_64/other_db | 764 kB 00:00:00 (12/12): updates/x86_64/primary_db | 7.4 MB 00:00:00 Metadata Cache Created