How to start docker daemon linux

Everything You want to know about Docker Daemon

On a typical installation the Docker daemon is started by a system utility, not manually by a user. This makes it easier to automatically start Docker when the machine reboots.

Configure Docker to start on boot

Most current Linux distributions (RHEL, CentOS, Fedora, Ubuntu 16.04 and higher) use systemd to manage which services start when the system boots. Ubuntu 14.10 and below use upstart.

$ sudo systemctl enable docker 

To disable this behavior, use disable instead.

$ sudo systemctl disable docker 

Start the daemon manually

If you don’t want to use a system utility to manage the Docker daemon, or just want to test things out, you can manually run it using the dockerd command. You may need to use sudo, depending on your operating system configuration.

When you start Docker this way, it runs in the foreground and sends its logs directly to your terminal.

$ dockerd INFO[0000] +job init_networkdriver() INFO[0000] +job serveapi(unix:///var/run/docker.sock) INFO[0000] Listening for HTTP on unix (/var/run/docker.sock) 

To stop Docker when you have started it manually, issue a Ctrl+C in your terminal.

Configure the Docker daemon

There are two ways to configure the Docker daemon:

• Use a JSON configuration file. This is the preferred option, since it keeps all configurations in a single place.
• Use flags when starting dockerd.

You can use both of these options together as long as you don’t specify the same option both as a flag and in the JSON file. If that happens, the Docker daemon won’t start and prints an error message.

To configure the Docker daemon using a JSON file, create a file at /etc/docker/daemon.json on Linux systems, or C:\ProgramData\docker\config\daemon.json on Windows. On MacOS go to the whale in the taskbar > Preferences > Daemon > Advanced, or locate ~/.docker/daemon.json.

Here’s what the configuration file looks like:

With this configuration the Docker daemon runs in debug mode, uses TLS, and listens for traffic routed to 192.168.59.3 on port 2376. You can learn what configuration options are available in the dockerd reference docs

You can also start the Docker daemon manually and configure it using flags. This can be useful for troubleshooting problems.

Here’s an example of how to manually start the Docker daemon, using the same configurations as above:

dockerd --debug \ --tls=true \ --tlscert=/var/docker/server.pem \ --tlskey=/var/docker/serverkey.pem \ --host tcp://192.168.59.3:2376 

You can learn what configuration options are available in the dockerd reference docs, or by running:

Docker daemon directory

The Docker daemon persists all data in a single directory. This tracks everything related to Docker, including containers, images, volumes, service definition, and secrets.

By default this directory is:

/var/lib/docker on Linux. C:\ProgramData\docker on Windows.

You can configure the Docker daemon to use a different directory, using the data-root configuration option.

Since the state of a Docker daemon is kept on this directory, make sure you use a dedicated directory for each daemon. If two daemons share the same directory, for example, an NFS share, you are going to experience errors that are difficult to troubleshoot.

Troubleshoot the daemon

You can enable debugging on the daemon to learn about the runtime activity of the daemon and to aid in troubleshooting. If the daemon is completely non-responsive, you can also force a full stack trace of all threads to be added to the daemon log by sending the SIGUSR signal to the Docker daemon.

Enable debugging

There are two ways to enable debugging. The recommended approach is to set the debug key to true in the daemon.json file. This method works for every Docker platform.

Edit the daemon.json file, which is usually located in /etc/docker/. You may need to create this file, if it does not yet exist. On macOS or Windows, do not edit the file directly. Instead, go to Preferences / Daemon / Advanced.

If the file is empty, add the following:

If the file already contains JSON, just add the key “debug”: true, being careful to add a comma to the end of the line if it is not the last line before the closing bracket. Also verify that if the log-level key is set, it is set to either info or debug. info is the default, and possible values are debug, info, warn, error, fatal.

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Start the daemon

This page shows how to start the daemon, either manually or using OS utilities.

Start the daemon using operating system utilities

On a typical installation the Docker daemon is started by a system utility, not manually by a user. This makes it easier to automatically start Docker when the machine reboots.

The command to start Docker depends on your operating system. Check the correct page under Install Docker.

Start with systemd

On some operating systems, like Ubuntu and Debian, the Docker daemon service starts automatically. Use the following command to start it manually:

$ sudo systemctl start docker 

If you want Docker to start at boot, see Configure Docker to start on boot.

Start the daemon manually

If you don’t want to use a system utility to manage the Docker daemon, or just want to test things out, you can manually run it using the dockerd command. You may need to use sudo , depending on your operating system configuration.

When you start Docker this way, it runs in the foreground and sends its logs directly to your terminal.

$ dockerd INFO[0000] +job init_networkdriver() INFO[0000] +job serveapi(unix:///var/run/docker.sock) INFO[0000] Listening for HTTP on unix (/var/run/docker.sock) 

To stop Docker when you have started it manually, issue a Ctrl+C in your terminal.

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Docker daemon configuration overview

This page shows you how to customize the Docker daemon, dockerd .

Configure the Docker daemon

There are two ways to configure the Docker daemon:

• Use a JSON configuration file. This is the preferred option, since it keeps all configurations in a single place.
• Use flags when starting dockerd .

You can use both of these options together as long as you don’t specify the same option both as a flag and in the JSON file. If that happens, the Docker daemon won’t start and prints an error message.

To configure the Docker daemon using a JSON file, create a file at /etc/docker/daemon.json on Linux systems, or C:\ProgramData\docker\config\daemon.json on Windows.

Here’s what the configuration file might look like:

 "builder":  "gc":  "defaultKeepStorage": "20GB", "enabled": true > >, "experimental": false > 

In addition to Docker Desktop default values, this configuration enables garbage collection at a 20GB threshold, and enables buildkit.

Using this configuration file, run the Docker daemon in debug mode, using TLS, and listen for traffic routed to 192.168.59.3 on port 2376 . You can learn what configuration options are available in the dockerd reference docs

You can also start the Docker daemon manually and configure it using flags. This can be useful for troubleshooting problems.

Here’s an example of how to manually start the Docker daemon, using the same configurations as shown in the previous JSON configuration:

$ dockerd --debug \ --tls=true \ --tlscert=/var/docker/server.pem \ --tlskey=/var/docker/serverkey.pem \ --host tcp://192.168.59.3:2376 

You can learn what configuration options are available in the dockerd reference docs, or by running:

Many specific configuration options are discussed throughout the Docker documentation. Some places to go next include:

You can configure most daemon options using the daemon.json file. One thing you can’t configure using daemon.json mechanism is an HTTP proxy. For instructions on using a proxy, see Configure Docker to use a proxy server.

Daemon data directory

The Docker daemon persists all data in a single directory. This tracks everything related to Docker, including containers, images, volumes, service definition, and secrets.

By default this directory is:

You can configure the Docker daemon to use a different directory, using the data-root configuration option. For example:

Since the state of a Docker daemon is kept on this directory, make sure you use a dedicated directory for each daemon. If two daemons share the same directory, for example, an NFS share, you are going to experience errors that are difficult to troubleshoot.

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