Jun 10 2015

The Parker Fund

Hello all,

I don’t usually post very personal things here on The Z-Issue, but rather use it for 1) posting information that may be of interest to others (e.g. solving technical problems [especially with regard to the world of Linux Engineering]), 2) mentioning articles that I found helpful, amusing, or otherwise interesting, or 3) just babbling about who knows what. This article, though, is about something that is very special to me, and one that is intimately and inextricably tied to who I am as a person.

For those of you who have read the about me page, you know that I have devoted the majority of my academic life to studies of Child and Adolescent Development / Psychology and Education. Understanding and helping children work through their difficult times is one of my biggest passions in this life.

Over the past decade or so, I’ve given a lot of thought to having children of my own and have decided that I would rather adopt than have kids who are biologically mine. My rationale is multifaceted, but primarily, I just think that there are enough children already here that could use loving homes, and I would like to offer that to one of them instead of bringing another one into the world. So, for several years now, I’ve been trying to put any little bit of extra money that I have into savings for adopting a child. In the past year, I have started to pursue adoption more actively from a lot of angles (discussing it with attorneys, researching adoption agencies and policies, et cetera). I have also tried to squirrel away even more money by doing side jobs and such. Though I’ve been relatively successful at saving money for the adoption, I have a very long way to go based on the estimate that I have been given (approximately $85,000 USD). At the time of this writing, I have saved a mere ~17% of the funds that I will need in order to get started on the process.

Why bring up any of these things about my personal life and goals? Simply put, the idea of crowdfunding is enticing in this situation. I post my articles hoping that they will help people who find themselves in similar situations (as mentioned, particularly relating to Linux, but also to travels, and so on) as the ones in which I have found myself over the years. And, thankfully, according to the analytics for the site and comments on various posts, people are finding the articles helpful. In particular, a couple of my Linux articles have been viewed tens of thousands of times on certain days. I’ll cut to the chase: if any of my articles have been helpful to you, please consider donating ANY amount that you comfortably can to The Parker Fund–helping me reach my goal of being able to adopt. Absolutely every dollar helps, so any donation will be greatly appreciated!

Why “The Parker Fund?” As I’ve said, I have more actively started to pursue the adoption within the past year or so. I’ve pondered many different aspects of the process, and have decided that I would like to adopt a boy first. I have also chosen the name Parker, and so to keep the goal alive and real in my mind, I refer to him by name, though he may not have even been born yet. Again, to keep my motivation up through setback after setback, I have started to decorate a room for him:


Parker's room
Click to enlarge

These types of little things help keep me focused on my goal, even if they seem a little premature.

So, in effort to expedite the start of the adoption process, if you can spare any funds and would like to help me, you may contribute to The Parker Fund by using the PayPal “Donate” button in the top widget on the right-hand side of the page. As I said, every dollar helps and will be greatly appreciated! Even if you can’t or don’t want to contribute, thank you for reading the Z-Issue and taking time out of your day to read about a personal aspiration that is very near and dear to my heart.

Cheers,
Zach

Jun 05 2015

RHEL/CentOS Kickstart partition scheme with disk by-path IDs and automation via PXE

So, for several weeks now, I’ve been struggling with disk naming and UDEV as they relate to RHEL or CentOS Kickstart automation via PXE. Basically, what used to be a relatively straight-forward process of setting up partitions based on disk name (e.g. /dev/sda for the primary disk, /dev/sdb for the secondary disk, and so on) has become a little more complicated due to the order in which the kernel may identify disks with UDEV implementations. The originally-used naming conventions of /dev/sdX may no longer be consistent across reboots or across machines. How this problem came to my attention was when I was Kickstarting a bunch of hosts, and realised that several of them were indicating that there wasn’t enough space on the drives that I had referenced. After doing some digging, I realised that some servers were identifying KVM-based media (like via a Cisco UCS CIMC interface), or other USB media as primary disks instead of the actual primary SCSI-based disks (SATA or SAS drives).

Though I agree that identifying disks by their path, their UUID, or an otherwise more permanent name is preferred to the ambiguous /dev/sdX naming scheme, it did cause a problem, and one that didn’t have a readily-identifiable workaround for my situation. My first thought was to use UUID, or gather the disk ID from /dev/disk/by-id/. However, that wouldn’t work because it wouldn’t be the same across all servers, so automatic installations via PXE wouldn’t be feasible. Next, I looked at referencing disks by their PCI location, which can be found within /dev/disk/by-path/. Unfortunately, I found that the PCI location might vary between servers as well. For example, I found:

Server 1:
/dev/disk/by-path/pci-0000:82:00.0-scsi-0:2:0:0 –> primary SCSI disk
/dev/disk/by-path/pci-0000:82:00.0-scsi-0:2:1:0 –> secondary SCSI disk

Server 2:
/dev/disk/by-path/pci-0000:0b:00.0-scsi-0:2:0:0 –> primary SCSI disk
/dev/disk/by-path/pci-0000:0b:00.0-scsi-0:2:1:0 –> secondary SCSI disk

That being said, I did notice one commonality between the servers that I used for testing. The primary and secondary disks (which, by the way, are RAID arrays attached to the same controller) all ended with ‘scsi-0:2:0:0 ‘ for the primary disk, and ‘scsi-0:2:1:0 ‘ for the secondary disk. Thinking that I could possibly just specify using a wildcard, I tried:

part /boot --fstype ext2 --size=100 --ondisk=disk/by-path/*scsi-0:2:0:0

but alas, that caused Anaconda to error out stating that the specified drive did not exist. At this point, I thought that all hope was lost in terms of automation. Then, however, I had a flash of genius (they don’t happen all that often). I could probably gather the full path ID in a pre-installation script, and then get the FULL path ID into the Kickstart configuration file with an include. Here are the code snippets that I wrote:


%pre --interpreter=/bin/bash
## Get the full by-path ID of the primary and secondary disks
osdisk=$(ls -lh /dev/disk/by-path/ | grep 'scsi-0:2:0:0 ' | awk '{print $9}')
datadisk=$(ls -lh /dev/disk/by-path/ | grep 'scsi-0:2:1:0 ' | awk '{print $9}')


## Create a temporary file with the partition scheme to be included in the KS config
echo "# Partitioning scheme" > /tmp/partition_layout
echo "clearpart --all" >> /tmp/partition_layout
echo "zerombr" >> /tmp/partition_layout
echo "part /boot --fstype ext2 --size=100 --ondisk=disk/by-path/$osdisk" >> /tmp/partition_layout
echo "part swap --recommended --ondisk=disk/by-path/$osdisk" >> /tmp/partition_layout
echo "part pv.01 --size=100 --grow --ondisk=disk/by-path/$osdisk" >> /tmp/partition_layout
echo "part pv.02 --size=100 --grow --ondisk=disk/by-path/$datadisk" >> /tmp/partition_layout
echo "volgroup vg_os pv.01" >> /tmp/partition_layout
echo "volgroup vg_data pv.02" >> /tmp/partition_layout
echo "logvol / --vgname=vg_os --size=100 --name=lv_os --fstype=ext4 --grow" >> /tmp/partition_layout
echo "logvol /data --vgname=vg_data --size=100 --name=lv_data --fstype=ext4 --grow" >> /tmp/partition_layout
echo "# Bootloader location" >> /tmp/partition_layout
echo "bootloader --location=mbr --driveorder=/dev/disk/by-path/$osdisk,/dev/disk/by-path/$datadisk --append=\"rhgb\"" >> /tmp/partition_layout
%end

Some notes about the pre-installation script would be: 1) yes, I know that it is a bit clumsy, but it functions despite the lack of elegance; 2) in lines 3 and 4, make sure that the grep statements include a final space. The final space (e.g. grep 'scsi-0:2:0:0 ' instead of just grep 'scsi-0:2:0:0') is important because the machine may have partitions already set up, and in that case, those partitions would be identified as '*scsi-0:2:0:0-part#' where # is the partition number.

So, this pre-installation script generates a file called /tmp/partition_layout that essentially has a normal partition scheme for a Kickstart configuration file, but references the primary and secondary SCSI disks (again, as RAID arrays attached to the same controller) by their full ‘by-path’ IDs. Then, the key is to include that file within the Kickstart configuration via:


# Partitioning scheme information gathered from pre-install script below
%include /tmp/partition_layout

I am happy to report that for the servers that I have tested thus far, this method works. Is it possible that there will be primary and secondary disks that are identified via different path IDs not caught by my pre-installation script? Yes, that is possible. It’s also possible that your situation will require a completely different pre-installation script to gather the unique identifier of your choice. That being said, I hope that this post will help you devise your method of reliably identifying disks so that you can create the partition scheme automatically via your Kickstart configuration file. That way, you can then deploy it to many servers via PXE (or any other implementation that you’re currently utilising for mass deployment).

Cheers,
Zach

May 22 2015

Three new quotes to the database

Today I added three new quotes to the “My Favourite Quotes” database that you see on the right-hand side of my blog.

“The evil people of the world would have little impact without the sheep.”
–Tim Clark

“Apologising does not always mean that you’re wrong and the other person is right. It just means that you value your relationship more than your ego.”
–Unknown

“Some day soon, perhaps in forty years, there will be no one alive who has ever known me. That’s when I will be truly dead – when I exist in no one’s memory. I thought a lot about how someone very old is the last living individual to have known some person or cluster of people. When that person dies, the whole cluster dies,too, vanishes from the living memory. I wonder who that person will be for me. Whose death will make me truly dead?”
–Irvin D. Yalom in Love’s Executioner and Other Tales of Psychotherapy

The first one came up during a conversation that I was having with a colleague who is absolutely brilliant. That quote in particular sums up a very simplistic idea, but one that would have a dramatic impact on human existence if we were to recognise our sometimes blind following of others.

Cheers,
Zach