[root@fm3 yum.repos.d]# yum update yum
Setting up Update Process
Setting up repositories
not using ftp, http[s], or file for repos, skipping - 4 is not a valid release or hasnt been released yet
Cannot find a valid baseurl for repo: update
Error: Cannot find a valid baseurl for repo: update
解决方法:
1.查看系统版本
lsb_release -a
访问 http://vault.centos.org/4.9/ (4.9是系统版本号)
下载repo: wget http://vault.centos.org/4.8/CentOS-Base.repo
覆盖 /etc/yum.repos.d/CentOS-Base.repo 文件
再试试,应该ok!