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I realize that processes that run inside Docker containers appear on the hosts' process list:

# ps aux | grep mariadb
root     12486  0.0  0.0 112812   976 pts/0    S+   14:47   0:00 grep --color=auto mariadb

Is there a way to identify whether a process is running on the Host or on a Docker container, or a way to filter the Docker processes out?

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  • You can check the following post: stackoverflow.com/questions/26659129/…
    – basekat
    Commented Feb 27, 2021 at 14:57
  • @basekat Thank you. I did try Googling several expressions hoping to find my answer, but I was only getting results of "docker ps" and other unhelpful stuff. That post does not seem to answer my question, however :) just explains what I already know.
    – Nuno
    Commented Feb 27, 2021 at 15:01
  • cat /proc/PID/cgroup, where PID is a process' PID on the host, tells you if a given process runs in a Docker container (from blog.stangroome.com/2017/12/05/…). Commented Feb 27, 2021 at 15:01
  • @berndbausch Very interesting! I may have the answer there! Thank you very much.
    – Nuno
    Commented Feb 27, 2021 at 15:02

3 Answers 3

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Found the answer.

To filter processes that are not running in Docker processes, we can use this:

ps -e -o pid,comm,cgroup | grep -v "/docker/"

So, for example, if I want to kill all "php-fpm" processes that are not running inside Docker, I can do:

kill -9 $(ps -e -o pid,comm,cgroup | grep -v "/docker/" | awk '$2 == "php-fpm" {print $1}')

0

If I quickly want to see what processes were started by what, I typically use a tool like htop (in tree mode by pressing F5), or pstree.

The output from pstree will look a bit like this:

systemd─┬─VGAuthService
        ├─abrt-dbus───3*[{abrt-dbus}]
        ├─abrt-watch-log
        ├─abrtd
        ├─chronyd
        ├─crond
        ├─dockerd─┬─docker-containe─┬─4*[docker-containe─┬─pause]
        │         │                 │                    └─9*[{docker-containe}]]
        │         │                 ├─docker-containe─┬─kube-apiserver───16*[{kube-apiserver}]
        │         │                 │                 └─9*[{docker-containe}]
        │         │                 ├─docker-containe─┬─kube-scheduler───14*[{kube-scheduler}]
        │         │                 │                 └─10*[{docker-containe}]
        │         │                 ├─docker-containe─┬─kube-controller───13*[{kube-controller}]
        │         │                 │                 └─10*[{docker-containe}]
        │         │                 ├─4*[docker-containe─┬─pause]
        │         │                 │                    └─10*[{docker-containe}]]
        │         │                 ├─docker-containe─┬─kube-proxy───12*[{kube-proxy}]
        │         │                 │                 └─9*[{docker-containe}]
        │         │                 ├─docker-containe─┬─node_exporter───31*[{node_exporter}]
        │         │                 │                 └─10*[{docker-containe}]
        │         │                 └─29*[{docker-containe}]
        │         └─47*[{dockerd}]

Which easily shows what processes are started by what.

htop lives within the in EPEL Repo, on RHEL.
pstree is installed by the psmisc package.

This isn't the most technical answer, but the best answer seems to already exist in a comment.

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  • Thank you. I appreciate the tips (I upvoted you). However, I'm looking for a way to do it straight with "ps", so I can easily get a list of PIDs, to pass to kill, for example.
    – Nuno
    Commented Feb 27, 2021 at 16:15
-1

cgroup 2.0 doesn't indicate that you're running in a docker container, nor does it work under Docker Desktop on Mac.

root@8a1d175a0b6c:/# ps -e -o pid,comm,cgroup PID COMMAND CGROUP 1 tini - 7 java - 3081 bash - 3282 ps -

You can look for /.dockerenv, but it's an empty file, so there's no unified, reliable way to get your own docker container Id. The Docker team really dropped the ball on this one.

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