I had a few virtualboxes running centos 5.7 that I hadn’t updated in a while. They were used for testing. Today I went to update them and couldn’t because the 5.7 repo’s had been deprecated and were not longer available. I found a quick way to do this, and this got my virtualboxes updated to 5.8……which is what I needed anyways.
sed -i 's/$releasever/5.8/g' /etc/yum.repos.d/CentOS-Base.repo
After you update to 5.8, then you need to reboot and change it back:
sed -i 's/5.8/$releasever/g' /etc/yum.repos.d/CentOS-Base.repo
And run yum updates again