Wednesday, August 21, 2013

Installing CentOS

In the past I have installed CentOS-6.0-i386-bin-DVD.iso in an ESX server by specifying "Linux, Other Linux (32-bit)", connecting the ISO and rebooting the box. This auto-launches the CentOS installer, from which I choose minimal install. This yeilds a console-only bare-bones OS appropriate for securely operating server software such as Apache HTTPD WebServer.

Looking at CentOS-6.2, I was confused by the ISO options.

CentOS-6.2-x86_64-LiveCD.iso      0.7G
CentOS-6.2-x86_64-LiveDVD.iso     1.6G
CentOS-6.2-x86_64-bin-DVD1.iso    4.1G
CentOS-6.2-x86_64-bin-DVD2.iso    1.2G
CentOS-6.2-x86_64-minimal.iso     0.3G
CentOS-6.2-x86_64-netinstall.iso  0.2G

I got totally the wrong idea from the release notes, wiki and superuser.com. I thought that LiveCD/DVD were bootable ISOs which will install CentOS, whereas the bin-DVD was a non bootable repository of packages which may not include an installer.

In fact the LiveCD/DVD is a bootable ISO that writes a fixed pre-installed image to the new box. Thus it is an OS install without an installer. Both the CD and DVD include a windows-style GUI, not suitable for operating secure server software. The difference between the CD and DVD is that the DVD contains more pre-installed packages/features.

CentOS-6.2-x86_64-bin-DVD1.iso is a bootable ISO that launches an installer that lets you choose a minimal install, suitable for operating secure server software. The minimal and netinstall ISOs contain just the bare bones OS and the ability to fetch more packages from the internet. The minimal.iso does not install the same packages as the "Minimal" option from the -bin- ISO.

I fetched my copy of the ISOs from mirror.symnds.com.

With our ESX server (vSphere/vCenter 5.1.0), there are three options for the CD/DVD drive: Client Device, Host Device, Datastore ISO File. As far as I know the "Host Device" means the actual physical drive on the ESX box and is therefore useless to users who don't have physical access to the ESX box. With centos6.0 I had no problem with "Client Device", which lets you select an ISO from your local machine.

The only trick is that you must power-on the virtual machine before you can select an ISO from the cd-wrench-icon in the vSphere topbar. At this stage your box is already at the no-os-found screen, but CTRL-ALT-INSERT will reboot it and boot into the connected ISO. As of centos6.2, this fails with all ISO options. the cd-wrench-icon menu gets stuck at "CD/DVD drive 1 Connecting...", and the console displays the following.

PXE-E53: No boot filename received
PXE-M0F: Exiting Intel PXE ROM
Operating System not found

The centos wiki for the minimal ISO suggest this problem can be solved by hosting the ISO on the ESX box and configuring the machine to connect to that ISO at boot, i.e. select "Datastore ISO File" and check "Connect at power on". This solution isn't ideal because I can't easily add ISOs to the ESX box, but I couldn't discover any other work-around.

Here's my CentOS 6.2 Install

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