Docker is a popular tool to build and run containerized applications. It is available for multiple platforms and used as one of the back-end container technologies in Kubernetes.
In Docker, you either build your own images to run your application as a container, or you can pull and use thousands of public images from the Docker repository and use them in your project. Once your image is ready, you can launch your containers using those images. A container is a running instance of a Docker image.
Managing Docker containers is one of the most important aspects to look after as a system administrator who manages Docker hosts/containers.
In this article, we’ll be focusing on managing containers using the docker command.
run Command
docker run
command is used to run a container from an image by specifying the Image ID
or the Repository
and/or Tag
name.
$ docker run {image}
Example:
$ docker run nginx
The above command runs an instance of <span class="NormalTextRun SpellingErrorV2 SCXW251451022 BCX0">nginx</span>
application on a docker host, if it already exists. If it doesn’t exist on the Docker host, it goes out to the docker hub (by default) and pulls the image down. But this is done the only first time. For subsequent times the same image is reused.
If you want to run a particular version of an image, specify its version separated by a colon. This is known as Tag
. In case you don’t specify any tag, docker will consider it by default as the latest.
Further, if you want to run the container in the background in a detached mode so that you get back to the prompt after Docker launches the container, use -d
flag.
Example:
$ docker run nginx
Unable to find image 'nginx:latest' locally
latest: Pulling from library/nginx
33847f680f63: Pull complete
dbb907d5159d: Pull complete
8a268f30c42a: Pull complete
b10cf527a02d: Pull complete
c90b090c213b: Pull complete
1f41b2f2bf94: Pull complete
Digest: sha256:8f335768880da6baf72b70c701002b45f4932acae8d574dedfddaf967fc3ac90
Status: Downloaded newer image for nginx:latest
/docker-entrypoint.sh: /docker-entrypoint.d/ is not empty, will attempt to perform configuration
/docker-entrypoint.sh: Looking for shell scripts in /docker-entrypoint.d/
/docker-entrypoint.sh: Launching /docker-entrypoint.d/10-listen-on-ipv6-by-default.sh
10-listen-on-ipv6-by-default.sh: info: Getting the checksum of /etc/nginx/conf.d/default.conf
10-listen-on-ipv6-by-default.sh: info: Enabled listen on IPv6 in /etc/nginx/conf.d/default.conf
/docker-entrypoint.sh: Launching /docker-entrypoint.d/20-envsubst-on-templates.sh
/docker-entrypoint.sh: Launching /docker-entrypoint.d/30-tune-worker-processes.sh
/docker-entrypoint.sh: Configuration complete; ready for start up
2021/08/15 12:13:23 [notice] 1#1: using the "epoll" event method
2021/08/15 12:13:23 [notice] 1#1: nginx/1.21.1
2021/08/15 12:13:23 [notice] 1#1: built by gcc 8.3.0 (Debian 8.3.0-6)
2021/08/15 12:13:23 [notice] 1#1: OS: Linux 5.8.0-1039-azure
2021/08/15 12:13:23 [notice] 1#1: getrlimit(RLIMIT_NOFILE): 1048576:1048576
2021/08/15 12:13:23 [notice] 1#1: start worker processes
2021/08/15 12:13:23 [notice] 1#1: start worker process 33
2021/08/15 12:13:23 [notice] 1#1: start worker process 34
ps Command
docker ps
command lists all running containers and some basic information about them. Like container ID, name of image, time container is created, current status, and name of the container. Each container gets a random name (if not specified explicitly) and ID.
Example:
$ docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
133f5e0267a5 nginx "/docker-entrypoint.…" 10 seconds ago Up 10 seconds 80/tcp jolly_elion
To list all the running and not running/exited containers at once, you can use:
$ docker ps -a
Example:
$ docker ps -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
fcec129f0eb4 nginx "/docker-entrypoint.…" 46 hours ago Exited (0) 46 hours ago interesting_ishizaka
6e8b1e441aa6 hello-world "/hello" 2 days ago Exited (0) 2 days ago keen_shirley
ls Command
Like ps
command, ls
can also be used for listing containers. -a
flag can be used to list all containers (not just the running ones).
$ docker container ls
Example:
$ docker container ls
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
15796e91c30b redis "docker-entrypoint.s…" 2 seconds ago Up 1 second 6379/tcp flamboyant_neumann
904390b65d45 nginx "/docker-entrypoint.…" 14 minutes ago Up 14 minutes 80/tcp nginx_new
$
stop Command
docker stop
command is used to stop a running container. Here we need to put container name or ID along with this.
$ docker stop {container-id}
On success, it would return the docker name or ID.
Example:
$ docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
133f5e0267a5 nginx "/docker-entrypoint.…" 50 seconds ago Up 49 seconds 80/tcp jolly_elion
This will return the CONTAINER ID
which you can use to stop the container.
$ docker stop 133f5
133f5
For this example and the coming ones, do note that you don’t need to specify a complete value of CONTAINER ID
. It’ll accept up to the part, which makes it unique among other running containers as Docker knows which container to stop.
rm Command
docker rm
command removes a stopped or exited container.
$ docker rm {CONTAINER NAME or ID}
Example:
$ docker rm 133f5
133f5
$
exec Command
We can use exec
command to go inside a running container. This is useful to debug running containers or do some stuff within a container.
$ docker exec –it {container} {command}
Example:
Suppose you want to launch bash
shell (assuming the image has Bash available, you can use other available shells as well) within a container named unruffled_meninsky
in interactive mode, use:
$ docker exec –it unruffled_meninsky /bin/bash
This should land you inside the container on a bash
shell. Here the flag -i
stands for interactive mode and -t
for the terminal. If you just wish to execute one or more commands and exit out from the container, you can use:
$ docker exec unruffled_meninsky cat /etc/hosts
127.0.0.1 localhost
::1 localhost ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters
172.17.0.2 cd2eed4acf34
logs Command
In case a container is launched in detached mode, and we want to see its logs, we can use logs
command to review its logs:
$ docker logs {CONTAINER NAME or ID}
Example:
$ docker logs 7da6dcebaf9c
/docker-entrypoint.sh: /docker-entrypoint.d/ is not empty, will attempt to perform configuration
/docker-entrypoint.sh: Looking for shell scripts in /docker-entrypoint.d/
/docker-entrypoint.sh: Launching /docker-entrypoint.d/10-listen-on-ipv6-by-default.sh
10-listen-on-ipv6-by-default.sh: info: Getting the checksum of /etc/nginx/conf.d/default.conf
10-listen-on-ipv6-by-default.sh: info: Enabled listen on IPv6 in /etc/nginx/conf.d/default.conf
/docker-entrypoint.sh: Launching /docker-entrypoint.d/20-envsubst-on-templates.sh
/docker-entrypoint.sh: Launching /docker-entrypoint.d/30-tune-worker-processes.sh
/docker-entrypoint.sh: Configuration complete; ready for start up
2021/08/15 12:14:09 [notice] 1#1: using the "epoll" event method
2021/08/15 12:14:09 [notice] 1#1: nginx/1.21.1
2021/08/15 12:14:09 [notice] 1#1: built by gcc 8.3.0 (Debian 8.3.0-6)
2021/08/15 12:14:09 [notice] 1#1: OS: Linux 5.8.0-1039-azure
2021/08/15 12:14:09 [notice] 1#1: getrlimit(RLIMIT_NOFILE): 1048576:1048576
2021/08/15 12:14:09 [notice] 1#1: start worker processes
2021/08/15 12:14:09 [notice] 1#1: start worker process 31
2021/08/15 12:14:09 [notice] 1#1: start worker process 32
$
cp Command
To copy files between a container and localhost filesystem, you can use cp
command.
$ docker container cp {CONTAINER NAME or ID:SRC_PATH} {DEST_PATH}|-
Example:
$ docker container cp quirky_cray:/etc/nginx/nginx.conf nginx.conf.bkp
export Command
Docker container command offers an option to export the filesystem of a container as a TAR file.
$ docker container export {CONTAINER NAME or ID}
inspect Command
We can check detailed information about a container using inspect
command as:
$ docker inspect {CONTAINER NAME or ID}
OR
$ docker container inspect {CONTAINER NAME or ID}
kill Command
A running container can be killed using kill
command with an optional --signal
or -s
flag. Multiple containers can be specified to kill them in one go.
$ docker kill {CONTAINER NAME or ID} [--signal VAL]
Example:
$ docker kill cd9005a0b5d2 -s 9
cd9005a0b5d2
$
stats Command
To display a live stream of a container’s resource usage, you can use stats
command:
$ docker container stats {CONTAINER NAME or ID}
Example:
$ docker container stats thirsty_volhard
CONTAINER ID NAME CPU % MEM USAGE / LIMIT MEM % NET I/O BLOCK I/O PIDS
904390b65d45 thirsty_volhard 0.00% 3.406MiB / 7.775GiB 0.04% 1.02kB / 0B 0B / 8.19kB 3
top Command
Like top
command in Linux, we can use it with Docker to get a list of running processes.
$ docker container top {CONTAINER NAME or ID}
Example:
$ docker container top thirsty_volhard
UID PID PPID C STIME TTY TIME CMD
root 2603 2582 0 12:34 ? 00:00:00 nginx: master process nginx -g daemon off;
systemd+ 2659 2603 0 12:34 ? 00:00:00 nginx: worker process
systemd+ 2660 2603 0 12:34 ? 00:00:00 nginx: worker process
$
rename Command
To rename an existing container, use rename
command.
$ docker container rename {OLD CONTAINER NAME} {NEW CONTAINER NAME}
Example:
$ docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
904390b65d45 nginx "/docker-entrypoint.…" 7 minutes ago Up 7 minutes 80/tcp nginx_container
$ docker container rename nginx_container nginx_new
$ docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
904390b65d45 nginx "/docker-entrypoint.…" 7 minutes ago Up 7 minutes 80/tcp nginx_new
$
diff Command
We can inspect changes to files or directories on a container’s filesystem with diff
command.
$ docker container diff {CONTAINER NAME or ID}
Example:
$ docker container diff nginx_new
C /var
C /var/cache
C /var/cache/nginx
A /var/cache/nginx/uwsgi_temp
A /var/cache/nginx/client_temp
A /var/cache/nginx/fastcgi_temp
A /var/cache/nginx/proxy_temp
A /var/cache/nginx/scgi_temp
C /etc
C /etc/nginx
C /etc/nginx/conf.d
C /etc/nginx/conf.d/default.conf
C /run
A /run/nginx.pid
$
Summary
To conclude, Docker offers an extensive set of commands to manage containers from their creation to destruction. We’ve covered some of the important commands and their usage in this article, which should give you a good idea about managing docker containers.