What does Used memory in Linux actually mean and how this concept has changed over the years.
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?
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…
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?
The procps developers are happy to announce that version 3.3.12 of procps was released today. This version has a mixture of bug fixes and enhancements. This unfortunately means another API bump but we are hoping this will be fixed with the new library API coming soon.
procps is developed on gitlab and the new version of procps can be found at https://gitlab.com/procps-ng/procps/tree/newlib
procps 3.3.12 can be found at https://gitlab.com/procps-ng/procps/tags/v3.3.12
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?
I looked at two interesting issues today around the ps program in the procps project. One had a solution and the other I’m puzzled about.
ps User-defined Format
Issue #9 was quite the puzzle. The output of ps changed depending if a different option had a hyphen before it or not.
First, the expected output
$ ps p $$ -o pid=pid,comm=comm pid comm 31612 bash
Next, the unusual output.
$ ps -p $$ -o pid=pid,comm=comm pid,comm=comm 31612
I have updated NEWS, bumped the API and tagged in git; procps version 3.3.11 is now released! This release we have fixed many bugs and made procps more robust for those odd corner cases. See the NEWS file for details. The most significant new feature in this release is the support for LXC containers in both…
I’m getting close to releasing version 3.3.11 of procps. When it gets near that time, I generally browse again the Debian Bug Tracker for procps bugs. Bug number #733758 caught my eye. With the free command if you used the s option before the c option, the s option failed, “seconds argument ‘N’ failed” where…
I have previously written about the gitlab CI runners that use docker. Yesterday I made some changes to procps and pushed them to gitlab which would then start the CI. This morning I checked and it said build failed – ok, so that’s not terribly unusual. The output from the runner was:
gitlab-ci-multi-runner 0.3.3 (dbaf96f) Using Docker executor with image csmall/testdebian ... Pulling docker image csmall/testdebian ... Build failed with Error: image csmall/testdebian: not found
Hmm, I know I have that image, it just must be the runner so, let’s see what images I have:
$ docker images REPOSITORY TAG IMAGE ID CREATED VIRTUAL SIZE
Now, I know I have images, I had about 10 or so of them, where did they go? I even looked in the /var/lib/docker directories and can see the json configs, what have you done with my images docker?