Category Archives: Sysadmin

FreeIPA: whoami via curl

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Assuming PRINCIPAL is your Kerberos principal and $IPASERVER is the FQDN of your server, you can query your identity on the IPA server via curl:

kinit $PRINCIPAL
curl -k -H referer:https://$IPASERVER/ipa   -H "Content-Type:application/json"    -H "Accept:applicaton/json"   --negotiate -u :   --cacert /etc/ipa/ca.crt   -d  '{"method":"whoami","params":[[],{"version": "2.220"}],"id":0}'   -X POST    https://$IPASERVER/ipa/json
{"result": {"object": "user", "command": "user_show/1", "arguments": ["ayoung"]}, "version": "4.5.4", "error": null, "id": 0, "principal": "ayoung@YOUNGLOGIC.COM"}

This is handy if your system is not registered as an IPA client.

To fetch by username:

curl -k -H referer:https://$IPASERVER/ipa   -H "Content-Type:application/json"    -H "Accept:applicaton/json" --negotiate -u : --cacert /etc/ipa/ca.crt -d '{"method": "user_show", "params": [[ "ayoung" ], { "all": true, "rights": true }  ]}'  -X POST    https://$IPASERVER/ipa/json

Scoped versus unscoped RBAC

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Role Based Access Control (RBAC) as defined by NIST is based on the concept of global roles. Global, in this case, means the scope of the application. So if you have the role of ADMIN, and you are in a globally scoped RBAC based application, that role applies to all APIs and resources within the program.

OpenStack was written assuming that the ADMIN role was a global role. But then it was implemented as a non-global role. It was implemented as a role scoped to a tenant. The term tenant was the original (and I would argue, better) term for what was later called Project, and then again expanded to Domains as well.

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Parsing a yum repo with XPath

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https://gnome.pages.gitlab.gnome.org/libxml2/xmllint.htmlLets say you want to see what src RPMs are in a given yum repo. If the author used createrepo to create the yum repo, it should be an a fairly standard layout. The following xpath query should pull it out.

Note that you can get xmllint to run the xpath query from libxml2


curl http://$yumserver/$somerepo/ > repo.html
xmllint --html  --xpath "//html/body/table/tr/td/a/@href" repo.html | grep src

The portion of the query a/@href will match a tag like this

<a href="https://blam.src.rpm">

More Personal Ansible

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I can do anything. I can’t do everything. –Me

Anything worth doing is worth doing in a way you can check in to git. To recall what I did from the command line, I should turn those actions into a persist-able document. Do I? Not often enough. Often I rely on bash history to remind me of what I did last time. Since the machines I work on are out of a global pool, I have been burned by not recording commands before relinquishing a machine.

For complex series of tasks, it makes sense to execute a bash script to perform those tasks, and I have many of these. Shell scripting excels in doing command line tasks. Where it does not do so well is on tasks that are split over multiple machines. While curl is great for pulling and pushing files to webservers, the majority of my remote work requires ssh and scp to set things up. This is where Ansible comes in: If I can make a playbook that records the commands I use to perform that action, I can repeat it on another machine.

Here is what my workflow looks like as I try to get better at it:

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Working with the Booked scheduler API

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One benefit of working in a hardware company is that you actually have hardware. I have worked in software for a long time, and I have learned to appreciate when new servers are not such a scarce resource as to impact productivity. However, hardware in our group needs to be shared amongst a large group of developers, and constantly reserved, assigned, and reprovisioned. We use an install of the booked scheduler to reserve servers. As with many tools, I am most interested in using it in a scripted fashion. Booked comes with an API. Here’s some of the things I can do with it.

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How not to waste time developing long-running processes

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Developing long running tasks might be my least favorite coding activity. I love writing and debugging code…I’d be crazy to be in this profession if I did not. But when a task takes long enough, your attention wanders and you get out of the zone.

Building the Linux Kernel takes time. Even checking the Linux Kernel out of git takes a non-trivial amount of time. The Ansible work I did back in the OpenStack days to build and tear down environments took a good bit of time as well. How do I keep from getting out of the zone while coding on these? It is hard, but here are some techniques.

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When to Ansible? When to Shell?

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Any new technology requires a mental effort to understand. When trying to automate the boring stuff, one decision I have to make is whether to use straight shell scripting or whether to perform that operation using Ansible. What I want to do is look at a simple Ansible playbook I have written, and then compare what the comparable shell script would look like to determine if it would help my team to use Ansible or not in this situation.

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