CentOS 6已经存在各种问题了，大家还是尽快放弃吧。

错误：

Loaded plugins: fastestmirror, refresh-packagekit, security
Setting up Update Process
Determining fastest mirrors
YumRepo Error: All mirror URLs are not using ftp, http[s] or file.
Eg. Invalid release/repo/arch combination/
removing mirrorlist with no valid mirrors: /var/cache/yum/x86_64/6/base/mirrorlist.txt
Error: Cannot find a valid baseurl for repo: base

经过测试，以下方法可以解决：

1. Go to /etc/yum.repos.d/ directory:
 # cd /etc/yum.repos.d/
2. Make copy of original file:
 # cp CentOS-Base.repo CentOS-Base.repo.old
3. Open and edit file with any text editor:
 # vi CentOS-Base.repo
4. Replace mirrorlist‘s
 Replace sections:
 [base]
[updates]
[extras]
With following:
 [base]
name=CentOS-$releasever - Base
# mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=os&infra=$infra
# baseurl=http://mirror.centos.org/centos/$releasever/os/$basearch/
baseurl=https://vault.centos.org/6.10/os/$basearch/
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-6
 # released updates
[updates]
name=CentOS-$releasever - Updates
# mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=updates&infra=$infra
# baseurl=http://mirror.centos.org/centos/$releasever/updates/$basearch/
baseurl=https://vault.centos.org/6.10/updates/$basearch/
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-6
 # additional packages that may be useful
[extras]
name=CentOS-$releasever - Extras
# mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=extras&infra=$infra
# baseurl=http://mirror.centos.org/centos/$releasever/extras/$basearch/
baseurl=https://vault.centos.org/6.10/extras/$basearch/
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-6
5. Clean yum cache
 # yum clean all
6. Run again yum update command:
 # yum update
Now you can successfully update your CentOS 6.

参考：https://arstech.net/centos-6-error-yumrepo-error-all-mirror-urls-are-not-using-ftp-http/