Docker Operations Commands

Docker operation commands are used to manage running containers and their processes

docker ps

Usage Command Description
Basic docker ps docker ps Shows all running containers.
Show All Containers docker ps -a Shows all containers, regardless of their status (running, exited, etc.).
Show Latest Created Container docker ps -l Shows the most recently created container, including all its details.
Show n Last Created Containers docker ps -n Shows the ‘n’ last created containers. Replace ‘n’ with the number of containers you want to list.
Show Containers & Size docker ps -s Shows all containers and their disk usage.

Remember, docker ps will show you the container ID, which is often required for other Docker commands such as docker start, docker stop, and docker rm

docker logs

Usage Command Description
Basic docker logs docker logs container_id Shows logs of a specific container. Replace container_id with the ID of the container you want to check.
Show last N lines docker logs --tail N container_id Shows the last N lines of output for a specific container. Replace N with the number of lines you want to see.
Show since a certain time docker logs --since '2023-08-03T10:10:09' container_id Shows the logs since a specific date or duration. In this example, the logs since August 3, 2023, 10:10:09.
Follow logs in real-time docker logs -f container_id Follows the logs output for a container in real-time, similar to tail -f.
Show timestamped logs docker logs --timestamps container_id Shows logs with timestamps for each log entry.

Remember that the docker logs command works on both running and stopped containers.

docker exec

This command opens an interactive Bash shell inside a running container named my_container. From there, you can run any command inside the container as if you were SSH-ed into a remote server. | Usage | Command | Description | | —– | ——- | ———– | | Basic docker exec | docker exec container_id command | Executes a command in a running container. Replace command with the command you want to run. | | Interactive exec | docker exec -it container_id /bin/bash | Starts an interactive bash shell in the container. | | As a different user | docker exec -u user container_id command | Runs a command as a specific user. Replace user with the user’s name. | | Detached exec | docker exec -d container_id command | Runs a command in a detached mode, in the background. | | Environment variables | docker exec -e VAR=value container_id command | Sets environment variables for the command being run. Replace VAR with the variable name and value with the corresponding value. |

The docker exec command is used to run a new command in a running Docker container. This can be incredibly useful for various purposes, including:

  1. Debugging: If you have a running container and you’re unsure why it’s not behaving as expected, docker exec can be used to start a shell in the context of the container. You can then use standard Linux commands to inspect the container’s file system, processes, network settings, etc.

  2. Administrative tasks: Maybe you need to change a configuration file, install a new package, or run a database migration. Using docker exec, you can run these tasks directly within the running container.

  3. Monitoring: With docker exec, you can fetch specific information about the state of a running container. This might be useful in monitoring and logging scenarios.

docker attach

Usage Command Description
Basic docker attach docker attach container_id Attaches your terminal’s standard input, output, and error (or any combination of the three) to a running container. Replace container_id with the ID or name of the container you want to attach to.
Detach without stopping the container docker attach container_id </br> CTRL-p CTRL-q After attaching to a container, you can detach from it without stopping the container by using the CTRL-p CTRL-q key sequence.
Attach & detach with options docker attach --detach-keys="ctrl-c" container_id This command allows you to customize the detach key sequence. In this example, CTRL-c is used.

Remember, if you attach to a container and then use CTRL-c, it will send a SIGINT to the container, which could stop it.

To avoid this, you can customize the detach keys or use the default CTRL-p CTRL-q key sequence to safely detach. For more options and details, check out the official Docker documentation.

docker kill

Usage Command Description
Basic docker kill docker kill container_id Sends a SIGKILL signal to a running container. This will immediately stop the container. Replace container_id with the ID or name of the container you want to kill.
Send specific signal docker kill --signal=SIGNAL container_id Sends a specific signal to the container. Replace SIGNAL with the signal you want to send (like SIGINT, SIGTERM, etc.).

Remember, docker kill will forcefully stop the container, which could lead to data loss if the container is in the middle of a write operation.

It’s generally recommended to use docker stop first, which sends a SIGTERM signal that allows the container to shut down gracefully.

If that doesn’t work, then you can use docker kill.

docker stop vs docker kill

  docker stop docker kill
Description Sends a SIGTERM signal to the main process in a container, asking it to shut down gracefully. If the process doesn’t exit within a certain timeframe (default is 10 seconds), a SIGKILL signal is sent to forcefully stop the container. Immediately sends a SIGKILL signal to a running container, forcibly terminating it.
When to use When you want to give a container the chance to clean up resources, save state, or perform other shutdown tasks. This is generally the recommended way to stop a container. When you need to immediately stop a container, typically during an error state or when the container is unresponsive. Be aware that it can lead to data loss, as it doesn’t give the container a chance to perform a graceful shutdown.
Command docker stop container_id docker kill container_id

Both docker stop and docker kill can be used to stop a running container, but their approach is different, and the choice between the two depends on whether you want to allow the container to shut down gracefully (docker stop) or you need to immediately terminate it (docker kill).

docker top

Usage Command Description
Basic docker top docker top container_id Shows the running processes in a specific container. Replace container_id with the ID or name of the container you want to check.
Custom format docker top container_id args This command lets you specify arguments to change the format of the output. Replace args with the arguments. For example, docker top container_id aux will use the aux format, similar to the ps aux command in Linux.

Remember, docker top gives you a snapshot of the processes running in a container at the moment you run the command.

It’s useful for debugging and understanding what’s happening inside a running container.

docker stats

Usage Command Description
Basic docker stats docker stats Displays a live stream of resource usage statistics for all running containers.
Stats for specific containers docker stats container_id1 container_id2 Displays live stream of resource usage statistics for specified containers. Replace container_id1, container_id2 with the IDs or names of the containers you want to check.
Stats with specific output format docker stats --format ": " Allows you to specify the output format. The example command will output the container name and the CPU usage percentage.
Stats without streaming docker stats --no-stream Gives a snapshot of the current statistics and exits instead of displaying a live stream.

docker stats gives you real-time information about CPU usage, memory usage, network IO, and more.

It’s an excellent tool for monitoring the performance of your containers.