总是出现Exiting on user cancel，导致不能正常安装。

这是yum的一个bug导致的问题。修改/usr/lib/python2.7/site-packages/urlgrabber/grabber.py

vi /usr/lib/python2.7/site-packages/urlgrabber/grabber.py
1510             elif errcode == 42:
1511                 # this is probably wrong but ultimately this is what happens
1512                 # we have a legit http code and a pycurl 'writer failed' code
1513                 # which almost always means something aborted it from outside
1514                 # since we cannot know what it is -I'm banking on it being
1515                 # a ctrl-c. XXXX - if there's a way of going back two raises to
1516                 # figure out what aborted the pycurl process FIXME
1517                 raise KeyboardInterrupt

修改后：

1510             #elif errcode == 42:
1511                 # this is probably wrong but ultimately this is what happens
1512                 # we have a legit http code and a pycurl 'writer failed' code
1513                 # which almost always means something aborted it from outside
1514                 # since we cannot know what it is -I'm banking on it being
1515                 # a ctrl-c. XXXX - if there's a way of going back two raises to
1516                 # figure out what aborted the pycurl process FIXME
1517             #    raise KeyboardInterrupt

然后以root用户运行如下命令升级：

yum clean metadata
yum clean all
yum upgrade

升级完成后运行yum命令安装即可。