the birdhouse in my soul

Some time ago, a CentOS install on a particular new Dell workstation needed the "nomodeset" kernel parameter to get a graphical login screen to correctly display. This was with a Radeon Firepro 2260 graphics card. After applying the CentOS 6.3 updates, Xorg wouldn't correctly detect the LCD panel's resolution anymore. A 1680x1050 panel would get a 1280x1024 resolution. In the days of digital DVI connections, DDC probing and what not, this was unusual and surprising. A lot of searching and testing led to the solution: the nomodeset parameter broke Xorg probing. Rebooting without the nomodeset parameter worked (no graphical problems like I had earlier), and solved the Xorg resolution probing.

VMware pre-compiles the VMware tools for selected OS kernels. The stock RHEL kernels are included, but not the intermediate updates. If you can live with that, you can simply add the VMware tools YUM repository: # cd /etc/yum.repos.d/ # wget http://bert.debruijn.be/linux-stuff/vmwaretools.repo and download the VMware RPM signing key # cd /etc/pki/rpm-gpg # wget http://packages.vmware.com/tools/VMWARE-PACKAGING-GPG-KEY.pub Then install the tools packages: # yum install vmware-tools-nox or # yum install vmware-tools vCenter will report the tools version as "Unmanaged" rather than "OK", but you have heartbeat (so HA and alarms can detect guest OS crashes), balloon driver, etc.

Red Hat and related distro's (like CentOS) use 1000 timer interrupts per second, per CPU core or thread (this is called the "HZ value" inside the kernel). Because this causes a lot of extra work in case of virtualization, and caused (past tense since RHEL 5.4!) problems with timekeeping, the " divider " kernel parameter has been introduced. For example, by booting with "divider=10", the kernel uses 100 timer interrupts instead of 1000, and "divider=25" means 40 timer interrupts per second. I did a little test today to see what difference that makes when running CentOS5.4 on vSphere. Tests were done with the current 2.6.18-164.11.1.el5 x86_64 kernel in a single vCPU VM. These are the results from my test environment: standard settings: HZ=1000: 60 MHz cycles used when idle. divider=2: HZ=500: 36 MHz cycles used when idle. divider=5: HZ=200: 25 MHz cycles used when idle. divider=10: HZ=100: 20 MHz cycles used when idle. divider=25: HZ=40: a...

When the SATA standard was introduced in PCs, I'd read that the electrical connections of both the data and the power connector had been designed with hotplug in mind. But just as with many hotplug-able technologies, I never actually tried it (hotplug PCI, anyone ?). Until now, that is. Job at hand: replace the software-mirrored SATA drives in high-end Dell workstations with bigger ones. Without losing the data, of course. A perfect opportunity to test how Linux handles SATA hotplug ! Actually, adding the drive was a breeze, Linux automatically detects the drive, and I could sfdisk, and mdadm --add. Next step was hot-removing the old drives: mdadm --fail and mdadm --remove, then physically unplug the drives. I didn't expect it to be so easy, to be honest. Great technology !

Fabian (of RPMforge and CentOS fame) wrote a blogpost about using pv (pipe viewer) to watch a datastream through a pipe, such as a dd-over-ssh copy from one machine to another. I knew pv existed, but I've often used dd on systems where pv wasn't available (e.g. rescue CD), or used dd without sending data through pipes. Even in these situations, you can keep an eye on dd's progress: open another terminal window, then run # while sleep 10; do killall -USR1 dd; done and switch back to the shell where dd is running. It will show its status every 10 seconds. Note, your version of dd needs to support this. The dd from RHEL3 doesn't (version 4), but the dd from RHEL5 does (version 5) !

Most Linux system-administrators are well aware of the benefits of LVM. With online resizing of filesystems and migration of data from one disk to another, it's fantastic. But don't assume that your system will do everything for you. If your system has one disk, that you used as a physical volume (PV) in a volume group (VG), where your root partition is stored as a logical volume (LV), you can easily add a new disk. Add the disk physically, boot up, use pvcreate and vgextend to include the new disk in the existing volume group. Just don't reboot, at least, not yet ! Your system requires a manual rebuild of its initial ram disk /sbin/mkinitrd -f /boot/initrd-2.6.18-92.1.10.el5.img 2.6.18-92.1.10.el5 If you forget to do this, your system will not boot, because it won't find all the components necessary to activate the VG it needs to access the root filesystem. Symptoms: kernel loads, initrd loads, root filesystem can't be mounted because the volume group doesn't e...

Are you still using Red Hat Enterprise Linux 2.1, or CentOS 2.1 ? Then this news is of great importance to you: planned End-Of-Life for these products is approaching ! After May 2009, there will be no more security updates for RHEL 2.1, nor support from Red Hat. It's not really news , as the lifecycle of RHEL products has always been clearly announced and published . If you missed all that, this is the time to start planning an upgrade. Your Red Hat subscription gives you the right to use the newer versions of RHEL, so upgrading is all you need to do. Need help planning an upgrade to RHEL 3, 4 or 5 ? I can recommend some experienced consultants ! ;-)