got this error when installing
or doing yum install




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

here is my centos-base.repo

[CODEBOX]
# CentOS-Base.repo
#
# This file uses a new mirrorlist system developed by Lance Davis for CentOS.
# The mirror system uses the connecting IP address of the client and the
# update status of each mirror to pick mirrors that are updated to and
# geographically close to the client. You should use this for CentOS updates
# unless you are manually picking other mirrors.
#
# If the mirrorlist= does not work for you, as a fall back you can try the
# remarked out baseurl= line instead.
#
#
[base]
name=CentOS-$releasever - Base
mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=os
#baseurl=http://centos.bio.lmu.de/$releasever/os/$basearch/
gpgcheck=1
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-centos4
priority=1
protect=1
enabled=1
#released updates
[update]
name=CentOS-$releasever - Updates
mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=updates
#baseurl=http://centos.bio.lmu.de/$releasever/updates/$basearch/
gpgcheck=1
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-centos4
priority=1
protect=1
enabled=1
#packages used/produced in the build but not released
[addons]
name=CentOS-$releasever - Addons
mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=addons
#baseurl=http://mirror.centos.org/centos/$releasever/addons/$basearch/
gpgcheck=1
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-centos4
#additional packages that may be useful
[extras]
name=CentOS-$releasever - Extras
mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=extras
#baseurl=http://mirror.centos.org/centos/$releasever/extras/$basearch/
gpgcheck=1
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-centos4
#additional packages that extend functionality of existing packages
[centosplus]
name=CentOS-$releasever - Plus
mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=centosplus
#baseurl=http://mirror.centos.org/centos/$releasever/centosplus/$basearch/
gpgcheck=1
enabled=0
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-centos4
#contrib - packages by Centos Users
[contrib]
name=CentOS-$releasever - Contrib
mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=contrib
#baseurl=http://mirror.centos.org/centos/$releasever/contrib/$basearch/
gpgcheck=1
enabled=0
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-centos4
[/CODEBOX]


here is my yum.conf

[CODEBOX]

[main]
cachedir=/var/cache/yum
debuglevel=2
logfile=/var/log/yum.log
pkgpolicy=newest
installonlypkgs=kernel kernel-smp kernel-devel kernel-smp-devel kernel-largesmp kernel-largesmp-devel kernel-hugemem kernel-hugemem-devel
distroverpkg=centos-release
tolerant=1
exactarch=1
retries=20
obsoletes=1
gpgcheck=1
plugins=1

# PUT YOUR REPOS HERE OR IN separate files named file.repo
# in /etc/yum.repos.d

[/CODEBOX]

4.8 is out of support so is probably no longer mirrored. Upgrade to 6.2

AS droyden said, 4.x is no longer supported. Might as well go for latest (6.2), but note you have to do a fresh install. Do NOT try to upgrade over 4.x install.

As of CentOS 4.8 there was the update to v 4.9.

so in order to upgrade your current v4.8 to 4.9 use:
good luck

I ran this to fix the problem:

pushd /etc/yum.repos.d
sed -i -e "s/baseurl=.*/baseurl=http:\/\/vault.centos.org\/4.9\/updates\/\$basearch\//g" CentOS-Base.repo
popd

Note that you've got have the right repo file for whatever RH-based distro you're running.

See post #2 & 3; its (4.x) been out of support for a while, inc security(!).
Get a current version.