下载新的CentOS-Base.repo 到/etc/yum.repos.d/

2.建立yum仓库

# yum install --downloadonly --downloaddir=/opt gcc
# ls /opt/
cpp-4.8.5-11.el7.x86_64.rpm        glibc-common-2.17-157.el7_3.1.x86_64.rpm   kernel-headers-3.10.0-514.2.2.el7.x86_64.rpm  libmpc-1.0.1-3.el7.x86_64.rpm
gcc-4.8.5-11.el7.x86_64.rpm        glibc-devel-2.17-157.el7_3.1.x86_64.rpm    libgcc-4.8.5-11.el7.x86_64.rpm                rh
glibc-2.17-157.el7_3.1.x86_64.rpm  glibc-headers-2.17-157.el7_3.1.x86_64.rpm  libgomp-4.8.5-11.el7.x86_64.rpm