Archive
Posts from 2017
Adding a new Operating System to the cobbler signature file
This has been an exciting week of code analysis and debugging. As I mentioned previously cobbler doesn't currently have support for Fedora 27. It it turns out adding a new Operating System signature is super easy. For my specific situation I forked the cobbler git repo and copied the Fedora 26 signature line and changed the 6 to a 7…
$ read more →Dealing With Cobbler Signature Errors
I wanted to test out a couple of Brendan Gregg's amazing eBPF scripts scripts this week. My home lab uses cobbler and ansible to provision systems and I was hoping to use Fedora 27 since it has a recent kernel. When I tried to import the Fedora 27 server DVD I received the following error: Cobbler keeps a set of distribution signatures in /var/lib/cobbler/distro_signatures.json which you can view with the cobbler signature report option: Each signature in this file is a JSON object defining how a given distribution is laid out. To update the contents of this file (which typically fixes the missing signature issue) you can use cobbler signature update: Updating the signature file unfortunately didn't fix my issue…
$ read more →Speeding Up Frequently Accessed System Calls With VDSO
While perusing the latest articles on hacker news I came across an amazing debugging article by Hector Martin. He recently tracked down a nasty segmentation violation and explained step-by-step how he did it. The article dicusses the VDSO (Virtual ELF Dynamic Shared Object) which is an efficient way to access frequently used system calls. Here is a nice description of this feature from the vdso(7) manual page: Why does the vDSO exist at all…
$ read more →Formatting CSS From The Linux Command Line
This morning I needed a way to pretty print a CSS style sheet. After poking around the web I came across the cssbeautify-cli utility which takes a CSS file and produces pretty printed output. To use this super useful tool you will first need to install and configure the node package manager (npm): To verify the module is available we can run npm with the search option: To install a module in $HOME/node_modules you can use the npm install option: If everything worked as expected a symbolic link to the executable should be created in $HOME/node_modules/.bin: To format a CSS file you can pass the file to the scripts "-f" option and redirect the pretty printed output to a new file (or a pager): This tool makes viewing and interpreting CSS a snap!
$ read more →Making sense of Javascript execution contexts and the scope Chain
Last night I spent a good deal of time studying javascript execution contexts and scoping rules. Most of my programming experience has been with shell, C, Python and Go. Most of these languages use lexical scoping but do so by the code block being executed. Javascript is a different animal when it comes to scoping…
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