Changing Grafana Legends
A quick tour of label_replace to fix Legend texts in Grafana for Prometheus data sources.
Percent CPU for processes
The ps program gives a snapshot of the processes running on your Unix-like system. On most Linux installations, this will be the ps program from the procps project. What does the %CPU field mean in the output of ps?
25 Years of Free Software
When did I start writing Free Software, now called Open Source? That’s a tricky question. Does the time start with the first file edited, the first time it compiles or perhaps even some proto-program you use to work out a concept for the real program formed later on.
So using the date you start writing, especially in a era before decent version control systems, is problematic. That is why I use the date of the first release of the first package as the start date. For me, that was Monday 24th July 1995.
…Sending data in a signal
The well-known kill system call has been around for decades and is used to send a signal to another process. The most common use is to terminate or kill another process by sending the KILL or TERM signal but it can be used for a form of IPC, usually around giving the other process a “kick” to do something.
One thing that isn’t as well known is besides sending a signal to a process, you can send some data to it. This can either be an integer or a pointer and uses similar semantics to the known kill and signal handler. I came across this when there was a merge request for procps. The main changes are using sigqueue instead of kill in the sender and using a signal action not a signal handler in the receiver.
…procps-ng 3.3.16
procps-ng version 3.3.16 was released today. Besides some documentation and library updates, there were a few incremental changes. Zombie Hunting with pgrep Ever wanted to find zombies? Perhaps processes with other states? pgrep has a shiny new runstate flag to help you which will match process against the runstate. I’m curious to see the use-cases…
psmisc 23.0
I had to go check but it has been over 3 years since the last psmisc release back in February 2014. I really didn’t think it had been that long ago. Anyhow, with no further delay, psmisc version 23.0 has been released today!
Update: 23.1 is out now, removed some debug line out of killall and shipped two missing documents.
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The sudo tty bug and procps
There have been recent reports of a security bug in sudo (CVE-2017-1000367) where you can fool sudo into thinking what controlling terminal it is running on to bypass its security checks. One of the first things I thought of was, is procps vulnerable to the same bug? Sure, it wouldn’t be a security bypass, but it would be a normal sort of bug. A lot of programs in procps have a concept of a controlling terminal, or the TTY field for either viewing or filtering, could they be fooled into thinking the process had a different controlling terminal?
Was I going to be in the same pickle as the sudo maintainers? The meat between the stat parsing sandwich? Can I find any more puns related somehow to the XKCD comic?
TLDR: No.
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Displaying Linux Memory
Memory management is hard, but RAM management may be even harder.
Most people know the vague overall concept of how memory usage is displayed within Linux. You have your total memory which is everything inside the box; then there is used and free which is what the system is or is not using respectively. Some people might know that not all used is used and some of it actually is free. It can be very confusing to understand, even for a someone who maintains procps (the package that contains top and free, two programs that display memory usage).
So, how does the memory display work?
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WordPress 4.0.1 fixes for Debian stable
Previously I posted a short article about the WordPress package for Debian and how that SID was getting the updated WordPress 4.0.1 which had some security fixes.
The question a lot of people were asking was: What about stable (or Wheezy). After way too much time due to other pressing issues, I have just uploaded the patched WordPress debian package for stable. The fixed version has the catchy number of 3.6.1~deb7u5. This package has all of the relevant patches that went in from WordPress 3.7.4 to 3.7.5 and there are even CVE IDs for this package (and 4.0.1 which all this stems from).
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Linux Capabilities
I was recently updating some code that uses fping. Initially it used exec() that was redirected to a temporary file but I changed it to use popen. While it had been a while since I’ve done this sort of thing, I do recall there was an issue with running popen on setuid binary. A later…