In this guide, we’ll explore how to manage Docker containers by stopping, pausing, resuming, and removing them. You’ll also learn how Linux signals map to Docker commands, plus best practices for cleaning up containers to reclaim resources.
1. Linux Signals Refresher Linux processes respond to signals for control and shutdown. Below is a quick overview:
Signal Action Description SIGSTOP Pause Suspends the process, cannot be caught. SIGCONT Resume Continues a paused process. SIGTERM Graceful shutdown Allows process cleanup before exit. SIGKILL Forceful kill Immediately terminates; cannot be trapped.
# Pause Apache httpd kill -SIGSTOP 11663 # Resume it kill -SIGCONT $( pgrep httpd ) # Graceful shutdown kill -SIGTERM $( pgrep httpd ) # Forceful kill kill -SIGKILL $( pgrep httpd ) # shorthand kill -9 $( pgrep httpd )
SIGTERM is the preferred way to stop a process because it allows cleanup. SIGKILL should be used only if the process does not terminate gracefully.
2. Docker Container Equivalents Docker uses similar primitives at the container level. The table below shows the mappings:
Action Linux Signal Docker Command Pause SIGSTOP/SIGCONT docker pause / docker unpauseStop SIGTERM → SIGKILL docker stopKill SIGKILL docker kill --signal=SIGKILLRemove — docker rm
2.1 Running an HTTPD Container docker run --name web httpd
2.2 Pause and Resume docker pause web docker unpause web
2.3 Stop (SIGTERM then SIGKILL) Docker sends SIGTERM, waits the default 10 seconds, then sends SIGKILL if the container is still running.
3. Sending Custom Signals You can target any signal to a container’s main process:
# Send SIGKILL by name docker kill --signal=SIGKILL web # Or by number docker kill --signal=9 web
4. Removing a Container Containers must be stopped before removal:
docker stop web docker rm web
Attempting to remove a running container yields an error:
$ docker rm web Error response from daemon: You cannot remove a running container ... Stop the container before attempting removal or use --force
5. Batch Stopping and Removing When managing multiple containers, leverage docker ps -q and docker ps -aq:
# Stop all running containers docker stop $( docker ps -q ) # Remove all containers (running & exited) docker rm $( docker ps -aq )
6. Pruning Stopped Containers To delete all stopped containers and free disk space:
docker container prune permanently deletes all stopped containers. There is no undoing this action.
7. Automatic Cleanup with —rm For ephemeral containers, use --rm to remove them automatically after exit:
docker run --rm ubuntu expr 4 + 5 # Output: 9
This is ideal for one-off tasks, CI jobs, or simple shell commands.
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