red hat

CentOS 7 Refusing VMware vSphere Guest OS Customizations

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So I just spent two hours of my life trying to get my CentOS 7 VM template to deploy correctly with a vSphere customization specification. No matter what I did it would customize the VM, then uncustomize it, essentially leaving me with the template again. I finally asked our oracle and savior, Google, and two amazing things occurred. First, I found the answer. About three weeks ago a fellow named Jeff Burns asked this same question on Server Fault, then answered his own question five minutes later (this is often what happens to me immediately upon filing a support case). He built on something I’d seen in /var/log/vmware-imc/toolsDeployPkg.log, where the VMware Tools couldn’t figure out what the OS is and …

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Gain 30% Linux Disk Performance with noatime, nodiratime, and relatime

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This is post #8 in my December 2013 series about Linux Virtual Machine Performance Tuning. For more, please see the tag “Linux VM Performance Tuning.” According to Red Hat’s Enterprise Linux 6 Power Management guide, the POSIX family of standards for operating systems “requires that operating systems maintain file system metadata that records when each file was last accessed.” This is called “atime” (a is for access) and is one of three timestamps Linux filesystems keep for their files (the other two are mtime and ctime, modify and change times). You can see these with the ‘stat’ command: $ stat /bin/ls File: `/bin/ls’ Size: 109208 Blocks: 216 IO Block: 4096 regular file Device: fd00h/64768d Inode: 519 Links: 1 Access: (0755/-rwxr-xr-x) …

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Store Logs Centrally

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This is post #7 in my December 2013 series about Linux Virtual Machine Performance Tuning. For more, please see the tag “Linux VM Performance Tuning.” It is universally true that over time a thin-provisioned virtual machine will slowly expand on disk. This happens because of the way files are deleted from disks. When files are written to disk the storage subsystem writes those blocks out, and the thinly-provisioned disk file grows a bit. But when a filesystem deletes a file all it does is update its own internal storage map to “forget” about the file. Nothing ever removes the data from the disk itself (which is why undelete utilities work, and why there are stringent procedures for securely erasing a …

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Use elevator=noop For Linux Virtual Machines

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This is post #6 in my December 2013 series about Linux Virtual Machine Performance Tuning. For more, please see the tag “Linux VM Performance Tuning.” Modern operating systems are fairly modular, and often have different modules to deal with memory, network I/O, and CPU scheduling. Disk I/O is no exception under Linux, as there are usually four different schedulers a sysadmin can choose from. Red Hat had a nice write-up on these a few years back and it remains relevant today: The Completely Fair Queuing (CFQ) scheduler is the default algorithm in Red Hat Enterprise Linux 4. As the name implies, CFQ maintains a scalable per-process I/O queue and attempts to distribute the available I/O bandwidth equally among all I/O …

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Why I Don't Use Third-Party Binary Packages

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There are a number of third-party package repositories out there for Linux distributions. For example, Fedora runs the Extra Packages for Enterprise Linux (EPEL) repository, which contains builds of open source software that isn’t supplied with Fedora or Red Hat Enterprise Linux. Similarly, a lot of projects have their own repositories that supply builds of software for OpenSUSE, Debian, Ubuntu, etc. Maybe it’s just because I’m old-school, and maybe it’s because I enjoy compiling things, but I really don’t like the idea of using binaries found on the Internet. I never have. As an aside, I really tried hard to make the rest of this post not be critical, or seem like criticism, but instead just be a reflection of …

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Strange Characters in My WordPress Blog

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In late August I moved my blog from a host running Red Hat Enterprise Linux 4 to a host running Red Hat Enterprise Linux 6. With it came an upgrade to MySQL, from 4 to 5. The migration itself seemed pretty painless, as I was able to recompile Apache on the new host and just copy everything over intact. I moved the databases by dumping each one and importing them on the other side. A week ago I was doing some work on the blog and noticed that for every apostrophe there were three other characters now: ’. I use a lot of apostrophes, and it sort of sucks to have every “it’s” become “it’s”. More specifically, it was only …

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How to Change SCSI Controllers on your Linux VM

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A question from Matt Vogt prompted this, where he wants to go from the BusLogic  SCSI controller to the LSI Logic SAS controller. It’s actually a straightforward conversion if you have the right steps. This is based on Red Hat Enterprise Linux 3, 4, and 5, but the principle should be the same for everything. It’s basically: snapshot, change config files, change hardware. Red Hat Enterprise Linux 6, in contrast, appears to have all the LSI Logic, parallel & SAS, drivers, as well as the paravirtual SCSI drivers, so all you need to do is shut the VM down and change the type of SCSI controller you’re using. I always recommend trying this on a test VM before you try …

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