Backgroud containers

Contents

• Backgroud containers

  • Objectives

  • A non-interactive container

  • Run a container in the background

  • List running containers

  • View only the IDs of the containers

  • Combining flags

  • View the logs of a container

  • View only the tail of the logs

  • Follow the logs in real time

  • Stop our container

  • Stopping our containers

  • Killing the remaining containers

Objectives

Our first containers were interactive.

We will now see how to:

• Run a non-interactive container.

• Run a container in the background.

• List running containers.

• Check the logs of a container.

• Stop a container.

• List stopped containers.

A non-interactive container

See also

• https://avril2018.container.training/intro.yml.html#97

$ docker run jpetazzo/clock

Unable to find image 'jpetazzo/clock:latest' locally
latest: Pulling from jpetazzo/clock
a3ed95caeb02: Pull complete
1db09adb5ddd: Pull complete
Digest: sha256:446edaa1594798d89ee2a93f660161b265db91b026491e4671c14371eff5eea0
Status: Downloaded newer image for jpetazzo/clock:latest
Wed May 30 08:34:23 UTC 2018
Wed May 30 08:34:24 UTC 2018
Wed May 30 08:34:25 UTC 2018
Wed May 30 08:34:26 UTC 2018
Wed May 30 08:34:27 UTC 2018
Wed May 30 08:34:28 UTC 2018
Wed May 30 08:34:29 UTC 2018

Run a container in the background

See also

• https://avril2018.container.training/intro.yml.html#98

Containers can be started in the background, with the -d flag (daemon mode)

$ docker run -d jpetazzo/clock

36935b2a967fd69c7fa23788e00855baa1896cc4af111fb78b9cfcc70a4d409c

• We don’t see the output of the container.

• But don’t worry: Docker collects that output and logs it!

• Docker gives us the ID of the container.

List running containers

See also

• https://avril2018.container.training/intro.yml.html#99

• docker ps

$ docker ps

CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS              PORTS               NAMES
36935b2a967f        jpetazzo/clock      "/bin/sh -c 'while d…"   3 minutes ago       Up 3 minutes                            lucid_kapitsa

Docker tells us:

• The (truncated) ID of our container.

• The image used to start the container.

• That our container has been running (Up) for a couple of minutes.

• Other information (COMMAND, PORTS, NAMES) that we will explain later

View only the IDs of the containers

See also

• https://avril2018.container.training/intro.yml.html#102

• docker ps

Many Docker commands will work on container IDs: docker stop, docker rm…

If we want to list only the IDs of our containers (without the other colums or the header line), we can use the -q (“Quiet”, “Quick”) flag:

docker ps -q

Combining flags

See also

• https://avril2018.container.training/intro.yml.html#102

• docker ps

We can combine -l and -q to see only the ID of the last container started:

$ docker ps -lq

3c181d8dbc4c

At a first glance, it looks like this would be particularly useful in scripts.

However, if we want to start a container and get its ID in a reliable way, it is better to use docker run -d, which we will cover in a bit.

View the logs of a container

See also

• https://avril2018.container.training/intro.yml.html#104

• docker logs

We told you that Docker was logging the container output.

Let’s see that now.

docker logs 3c18

Wed May 30 08:49:15 UTC 2018
Wed May 30 08:49:16 UTC 2018
Wed May 30 08:49:17 UTC 2018
Wed May 30 08:49:18 UTC 2018
Wed May 30 08:49:19 UTC 2018
Wed May 30 08:49:20 UTC 2018
Wed May 30 08:49:21 UTC 2018
Wed May 30 08:49:22 UTC 2018
Wed May 30 08:49:23 UTC 2018
Wed May 30 08:49:24 UTC 2018
Wed May 30 08:49:25 UTC 2018
Wed May 30 08:49:26 UTC 2018
Wed May 30 08:49:27 UTC 2018

View only the tail of the logs

See also

• https://avril2018.container.training/intro.yml.html#104

• docker logs

To avoid being spammed with eleventy pages of output, we can use the –tail option:

$ docker logs 3c18 --tail 3

Wed May 30 09:02:29 UTC 2018
Wed May 30 09:02:30 UTC 2018
Wed May 30 09:02:31 UTC 2018

The parameter is the number of lines that we want to see.

Follow the logs in real time

See also

• https://avril2018.container.training/intro.yml.html#106

• docker logs

Just like with the standard UNIX command tail -f, we can follow the logs of our container:

$ docker logs --follow 3c18 --tail 1

Wed May 30 09:07:11 UTC 2018
Wed May 30 09:07:12 UTC 2018
Wed May 30 09:07:13 UTC 2018
Wed May 30 09:07:14 UTC 2018
Wed May 30 09:07:15 UTC 2018

• This will display the last line in the log file.

• Then, it will continue to display the logs in real time.

• Use ^C to exit.

Stop our container

See also

• https://avril2018.container.training/intro.yml.html#107

• docker stop

There are two ways we can terminate our detached container.

• Killing it using the docker kill command.

• Stopping it using the docker stop command.

The first one stops the container immediately, by using the KILL signal.

The second one is more graceful. It sends a TERM signal, and after 10 seconds, if the container has not stopped, it sends KILL.

Reminder: the KILL signal cannot be intercepted, and will forcibly terminate the container.

Stopping our containers

See also

• https://avril2018.container.training/intro.yml.html#108

• docker stop

Let’s stop one of those containers:

$ docker stop 3c1

3c1

This will take 10 seconds:

• Docker sends the TERM signal;

• the container doesn’t react to this signal (it’s a simple Shell script with no special signal handling);

• 10 seconds later, since the container is still running, Docker sends the KILL signal;

• this terminates the container.

Killing the remaining containers

See also

• https://avril2018.container.training/intro.yml.html#109

• docker stop

Let’s be less patient with the two other containers:

$ docker stop 1fe 369

1fe
369

The stop and kill commands can take multiple container IDs.

Those containers will be terminated immediately (without the 10 seconds delay).

Let’s check that our containers don’t show up anymore:

$ docker ps

CONTAINER ID        IMAGE               COMMAND             CREATED             STATUS              PORTS               NAMES