Docker kill process inside container - bash

Question

I exec into Docker container with docker exec -it container-name bash
Inside container I run command ps aux | grep processName
I receive a PID and after that I run:
kill processId but receive:
-bash: kill: (21456) - No such process
Am I missing something or? I know that Docker shows different process IDs from top command inside the host and ps aux inside the container (How to kill process inside container? Docker top command), but I am running this from inside container?

Answer 1

That response is because the process you are trying to kill is not existing at the moment of killing it. For example, if you launch ps aux you can get an output like this inside a container (it depends of the container of course):
oot#69fbbc0ff80d:/# ps aux
USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND
root 1 0.0 0.0 18400 3424 pts/0 Ss 13:55 0:00 bash
root 15 0.0 0.0 36840 2904 pts/0 R+ 13:57 0:00 ps aux
Then if you try to kill process with PID 15 you'll get the error because PID 15 is finished at the moment of trying to kill it. The ps command terminates after showing you the processes info. So:
root#69fbbc0ff80d:/# kill 15
bash: kill: (15) - No such process
In a docker container you can kill process in the same way as normal excepting the root process (id 1). You can't kill it:
root#69fbbc0ff80d:/# ps aux
USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND
root 1 0.0 0.0 18400 3424 pts/0 Ss 13:55 0:00 bash
root 16 0.0 0.0 36840 2952 pts/0 R+ 13:59 0:00 ps aux
root#69fbbc0ff80d:/# kill 1
root#69fbbc0ff80d:/# ps aux
USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND
root 1 0.0 0.0 18400 3424 pts/0 Ss 13:55 0:00 bash
root 17 0.0 0.0 36840 2916 pts/0 R+ 13:59 0:00 ps aux
As you can see you can't kill it. Anyway if you want to proof that you can kill processes you can do:
root#69fbbc0ff80d:/# ps aux
USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND
root 1 0.0 0.0 18400 3424 pts/0 Ss 13:55 0:00 bash
root 18 0.0 0.0 36840 3064 pts/0 R+ 14:01 0:00 ps aux
root#69fbbc0ff80d:/# sleep 1000 &
[1] 19
root#69fbbc0ff80d:/# ps aux
USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND
root 1 0.0 0.0 18400 3424 pts/0 Ss 13:55 0:00 bash
root 19 0.0 0.0 4372 724 pts/0 S 14:01 0:00 sleep 1000
root 20 0.0 0.0 36840 3016 pts/0 R+ 14:01 0:00 ps aux
root#69fbbc0ff80d:/# kill 19
root#69fbbc0ff80d:/# ps aux
USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND
root 1 0.0 0.0 18400 3424 pts/0 Ss 13:55 0:00 bash
root 21 0.0 0.0 36840 2824 pts/0 R+ 14:01 0:00 ps aux
[1]+ Terminated sleep 1000
Hope it helps.