Archive for 'Linux Kernel'

How to ensure sure you can boot if your initrd image has problems

I was playing around with some new kernel bits a few weeks back, and needed to update my initrd image. Having encountered various situations where a box wouldn’t boot due to a botched initrd file, I have become overly protective of this file. Now each time I have to perform an update, I will first […]

2.6.32 Linux kernel Virtualization memory De-Duplication

This is pretty sweet.  In the 2.6.32 Linux kernel released yesterday, a new feature of de-duplicating memory of virtualized instances, was introduced. Modern operative systems already use memory sharing extensively, for example forked processes share initially with its parent all the memory, there are shared libraries, etc. Virtualization however can’t benefit easily from memory sharing. […]

How the Linux OOM killer works

Most admins have probably experienced failures due to applications leaking memory, or worse yet consuming all of the virtual memory (physical memory + swap) on a host. The Linux kernel has an interesting way of dealing with memory exhaustion, and it comes in the way of the Linux OOM killer. When invoked, the OOM killer […]

Scanning SCSI controllers for new LUNs on Centos and Fedora Linux hosts

While building out a new ESX guest, I had to scan for a new SCSI device I added. To scan a SCSI controller for new LUNs, you can echo the “- – -” string to the SCSI controller’s scan sysfs node: $ echo “- – -” > /sys/class/scsi_host/host0/scan Now you may be asking yourself, what […]

Managing /etc/sysctl.conf with the sysctl utility

The Linux kernel provides the sysctl interface to modify values that reside under the /proc/sys directory. Sysctl values are typically stored in /etc/sysctl.conf, and are applied using the sysctl utility. To set a sysctl variable to a specific value, you can run sysctl with the “-w” (change a specific sysctl variable) option: $ sysctl -w […]

Viewing the contents of an initrd image

I was doing some research tonight, and needed to look inside my initrd image to see if a couple of device drivers were present. Initrd images are stored as compressed cpio archives, which allows a pipeline like the following to be used to extract the contents of an image: $ gunzip < initrd-2.6.29.4-167.fc11.x86_64.img | cpio […]

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