Why does a docker cli command exit with status 1 on a SIGTERM signal?

Question

When I run a docker CLI command and send a SIGTERM signal to the process running the docker command, I would expect the process to exit with status 143 representing the SIGTERM but it actually exits with status 1. Why is this the case?

(shell 1)
$ docker run -it --rm alpine:latest sleep 1000

(shell 2)
$ ps | grep docker
75658 ttys000    0:00.03 docker run -it --rm alpine:latest sleep 1000

(shell 2)
$ kill -SIGTERM 75658

(shell 1)
...container stops running
$ echo $?
1 (was expecting 143)

On the other hand, it returns with the expected status (137) when I end the process with a SIGKILL.

BMitch · Accepted Answer · 2024-07-10 18:33:30Z

You didn't kill the sleep command, you killed the docker CLI:

$ ps -ef | grep sleep
bmitch    949110   10662  0 14:26 pts/11   00:00:00 docker run -it --rm alpine:latest sleep 1000
root      949193  949173  0 14:26 pts/0    00:00:00 sleep 1000
bmitch    949223   10618  0 14:27 pts/10   00:00:00 grep sleep

Which means killing the docker process just exits the command, the container is still running and there's no exit code passed through:

$ docker run -it --rm alpine:latest sleep 1000
context canceled

# the above message appears after running a kill -SIGTERM 949110 command in another terminal

$ docker ps -l
CONTAINER ID   IMAGE           COMMAND        CREATED          STATUS          PORTS     NAMES
e62c8f6d2424   alpine:latest   "sleep 1000"   21 seconds ago   Up 21 seconds             awesome_morse

The sleep command itself doesn't respond to SIGTERM for me, but it does respond to SIGKILL:

$ docker run -it --rm alpine:latest sleep 1000

# from another terminal, kill the sleep process itself
# this requires sudo since it is running as root

$ echo $?
137

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