I ran into an interesting issue with a “minimal” CentOS installation and had to help a colleague install Yum on a server where only rpm existed. Here’s the final RPM line I used:

rpm -Uvh http://mirror.centos.org/centos/5/os/x86_64/CentOS/yum-3.2.22-37.el5.centos.noarch.rpm http://mirror.centos.org/centos/5/os/x86_64/CentOS/python-elementtree-1.2.6-5.x86_64.rpm http://mirror.centos.org/centos/5/os/x86_64/CentOS/python-iniparse-0.2.3-4.el5.noarch.rpm http://mirror.centos.org/centos/5/os/x86_64/CentOS/python-sqlite-1.1.7-1.2.1.x86_64.rpm http://mirror.centos.org/centos/5/os/x86_64/CentOS/rpm-python-4.4.2.3-22.el5.x86_64.rpm http://mirror.centos.org/centos/5/os/x86_64/CentOS/python-urlgrabber-3.1.0-6.el5.noarch.rpm http://mirror.centos.org/centos/5/os/x86_64/CentOS/yum-fastestmirror-1.1.16-16.el5.centos.noarch.rpm http://mirror.centos.org/centos/5/os/x86_64/CentOS/yum-metadata-parser-1.1.2-3.el5.centos.x86_64.rpm http://mirror.centos.org/centos/5/os/x86_64/CentOS/rpm-4.4.2.3-22.el5.x86_64.rpm http://mirror.centos.org/centos/5/os/x86_64/CentOS/rpm-libs-4.4.2.3-22.el5.x86_64.rpm http://mirror.centos.org/centos/5/os/x86_64/CentOS/popt-1.10.2.3-22.el5.x86_64.rpm http://mirror.centos.org/centos/5/os/x86_64/CentOS/m2crypto-0.16-8.el5.x86_64.rpm http://mirror.centos.org/centos/5/os/x86_64/CentOS/libxml2-2.6.26-2.1.12.x86_64.rpm http://mirror.centos.org/centos/5/os/x86_64/CentOS/logrotate-3.7.4-12.x86_64.rpm http://mirror.centos.org/centos/5/os/x86_64/CentOS/expat-1.95.8-8.3.el5_5.3.x86_64.rpm http://mirror.centos.org/centos/5/os/x86_64/CentOS/nss-3.12.8-4.el5_6.x86_64.rpm http://mirror.centos.org/centos/5/os/x86_64/CentOS/nspr-4.8.6-1.el5_5.x86_64.rpm

This should install Yum and all the required depedancies for CentOS 5 x86_64 (at the time of this writing). Once this is ran, yum should be available to install any other software needed.

[root@vps ~]# /etc/init.d/sshd restart
Stopping sshd:                                             [FAILED]
Generating SSH1 RSA host key:                              [FAILED]

I delved a little further and discovered that ssh-keygen was failing:

[root@vps ~]# ssh-keygen
cannot read from /dev/urandom, No such file or directory

And finally, from there, I generated the urandom file:

/sbin/MAKEDEV urandom

Also, to ensure on restarts the urandom file (as well as pty and tty) are created, I added the following to /etc/rc.d/rc.local:

/sbin/MAKEDEV pty
/sbin/MAKEDEV tty
/sbin/MAKEDEV urandom

Hopefully this helps if you run into a similar issue down the line!

Today I ran into an interesting issue where a VPS had no networking either inbound or outbound after setup. This is the error that would present when restarting network via init.d:

Bringing up interface venet0:
SIOCADDRT: Network is unreachable
SIOCADDRT: Network is unreachable

This issue also presented in that cPanel licenses could not activate not could any ping or host commands work properly. I eventually narrowed down the issue to the fact that the IPs that had been added to the VPS were not properly set to ARP by checking with the following command (run on the node):

arp | grep [INSERT IP HERE]

In order to resolve this, all I needed to do was add the arp entries for the IPs on the actual virtual environment by running the following commands on the node:

arp -s [INSERT IP HERE] `ifconfig eth0 | grep eth0 | awk '{print $5}'` pub

Make sure you run the command above for every IP on the VPS. This resolved the issue and all networking started working again properly.

yum install xen PyXML mesa-libGL
yum remove xen python-virtinst libvirt-python libvirt xen-libs
mkdir rpms
cd rpms
wget http://www.gitco.de/repo/xen3.4.3/libvirt-0.7.0-6.el5.x86_64.rpm
wget http://www.gitco.de/repo/xen3.4.3/libvirt-client-0.7.0-6.el5.x86_64.rpm
wget http://www.gitco.de/repo/xen3.4.3/libvirt-python-0.7.0-6.el5.x86_64.rpm
wget http://www.gitco.de/repo/xen3.4.3/python-virtinst-0.500.0-1.el5.noarch.rpm
wget http://www.gitco.de/repo/xen3.4.3/xen-3.4.3-1.el5.x86_64.rpm
wget http://www.gitco.de/repo/xen3.4.3/xen-libs-3.4.3-1.el5.x86_64.rpm
wget http://www.gitco.de/repo/xen3.4.3/glusterfs-client-2.0.8-1.el5.x86_64.rpm
wget http://www.gitco.de/repo/xen3.4.3/glusterfs-common-2.0.8-1.el5.x86_64.rpm
wget http://www.gitco.de/repo/xen3.4.3/fuse-2.7.4-1.rf.x86_64.rpm
wget http://www.gitco.de/repo/xen3.4.3/libibverbs-1.1-1.x86_64.rpm
rpm -ivh *.rpm

After that block, make sure you edit /etc/grub.conf to set the following lines:

---snip---
default = 0
---snip---
kernel /xen.gz-3.4.3 dom0_mem=512m
---snip---

The first will set the xen kernel as the default and the second will limit dom0 to only be able to use 512m of memory, leaving the rest for your VEs. After these changes, go ahead and reboot. Let me know if this route works for you!