How do I make Docker (or podman, for that matter - interested in a solution for both or just one) re-run the CMD of a stopped container?
I've got this barebone Dockerfile:
FROM alpine
CMD ["date"]
I build it:
$ podman build -t reruncmd .
STEP 1: FROM alpine
STEP 2: CMD ["date"]
STEP 3: COMMIT reruncmd
--> 32ef88d23c0
Successfully tagged localhost/reruncmd:latest
32ef88d23c04eeb8b8bbafb1dc2851e9ce046fb88dbfddea020c16c3a1944461
Then I run it:
$ podman run --name re-run-cmd reruncmd
Fri Jun 18 06:20:33 UTC 2021
Now it's obviously stopped:
$ podman ps -a --filter 'name=^/?re-run-cmd$'
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
2795e08162e1 localhost/reruncmd:latest date 2 minutes ago Exited (0) 2 minutes ago re-run-cmd
But when I restart the container, the CMD isn't run again:
$ podman container restart re-run-cmd
2795e08162e1089eb639098a804ec7d8743ed274d4d7acbdc97f6b07ec1ecdfe
What do I need to change?
I used podman in my examples above; get the exact same behaviour with docker:
$ docker build -t reruncmd .
[+] Building 14.4s (6/6) FINISHED
=> [internal] load build definition from Dockerfile 0.2s
=> => transferring dockerfile: 69B 0.2s
=> [internal] load .dockerignore 0.0s
=> => transferring context: 2B 0.0s
=> [internal] load metadata for docker.io/library/alpine:latest 10.7s
=> [auth] library/alpine:pull token for registry-1.docker.io 0.0s
=> [1/1] FROM docker.io/library/alpine@sha256:234cb88d3020898631af0ccbbcca9a66ae7306ecd30c9720690858c1b007d2a0 3.1s
=> => resolve docker.io/library/alpine@sha256:234cb88d3020898631af0ccbbcca9a66ae7306ecd30c9720690858c1b007d2a0 0.0s
=> => sha256:234cb88d3020898631af0ccbbcca9a66ae7306ecd30c9720690858c1b007d2a0 1.64kB / 1.64kB 0.0s
=> => sha256:1775bebec23e1f3ce486989bfc9ff3c4e951690df84aa9f926497d82f2ffca9d 528B / 528B 0.0s
=> => sha256:d4ff818577bc193b309b355b02ebc9220427090057b54a59e73b79bdfe139b83 1.47kB / 1.47kB 0.0s
=> => sha256:5843afab387455b37944e709ee8c78d7520df80f8d01cf7f861aae63beeddb6b 2.81MB / 2.81MB 1.0s
=> => extracting sha256:5843afab387455b37944e709ee8c78d7520df80f8d01cf7f861aae63beeddb6b 1.9s
=> exporting to image 0.0s
=> => exporting layers 0.0s
=> => writing image sha256:c5faac680f09542b5efbfc9f9f9fe40265ea17e0654a47ac67040cf2f14473fc 0.0s
=> => naming to docker.io/library/reruncmd 0.0s
Use 'docker scan' to run Snyk tests against images to find vulnerabilities and learn how to fix them
$ docker run --name re-run-cmd reruncmd
Fri Jun 18 06:25:47 UTC 2021
$ docker ps -a --filter 'name=^/?re-run-cmd$'
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
0a3bfcc42814 reruncmd "date" 11 seconds ago Exited (0) 8 seconds ago re-run-cmd
$ docker container restart re-run-cmd
re-run-cmd
$ docker container start re-run-cmd
re-run-cmd
Actually, CMD is executed at every start. You have been misled by the fact that docker start does not show you the result of CMD. If you run docker start with -a or --attach key, you will see the output.
❯ docker run --name test debian echo hi
hi
❯ docker start test
test
❯ docker start -a test
hi
❯ docker logs test
hi
hi
hi
As you see from the last command, there were exactly three runs.