Centos 无法直接通过yum安装7z，我们一般通过repoforge,rpmforge的软件包进行安装，你只需要下载一个对应的包，直接安装就可以
p7zip-9.20.1-1.el4.rf.i386.rpm 4.6M RHEL4 and CentOS-4 x86 32bit
p7zip-9.20.1-1.el4.rf.x86_64.rpm 4.7M RHEL4 and CentOS-4 x86 64bit
p7zip-9.20.1-1.el5.rf.i386.rpm 4.2M RHEL5 and CentOS-5 x86 32bit
p7zip-9.20.1-1.el5.rf.x86_64.rpm 4.3M RHEL5 and CentOS-5 x86 64bit
p7zip-9.20.1-1.el6.rf.i686.rpm 3.8M RHEL6 and CentOS-6 x86 32bit
p7zip-9.20.1-1.el6.rf.x86_64.rpm 3.9M RHEL6 and CentOS-6 x86 64bit
wget http://pkgs.repoforge.org/p7zip/p7zip-9.20.-.el5.rf.i386.rpm
rpm -ivh p7zip-9.20.-.el5.rf.i386.rpm
更多新版本请进入:http://pkgs.repoforge.org/p7zip/