Configuring and running Docker on various distributions

After successfully installing Docker, the docker daemon runs with its default configuration.

In a production environment, system administrators typically configure the docker daemon to start and stop according to an organization‘s requirements. In most cases, the system administrator configures a process manager such as SysVinit, Upstart, or systemd to manage the docker daemon’s start and stop.

Running the docker daemon directly

The docker daemon can be run directly using the -d option. By default it listens on the Unix socket unix:///var/run/docker.sock

$ docker daemon

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)
...
...

Configuring the docker daemon directly

If you're running the docker daemon directly by running docker daemon instead of using a process manager, you can append the configuration options to the docker run command directly. Other options can be passed to the docker daemon to configure it.

Some of the daemon's options are:

Flag	Description
`-D`, `--debug=false`	Enable or disable debug mode. By default, this is false.
`-H`,`--host=[]`	Daemon socket(s) to connect to.
`--tls=false`	Enable or disable TLS. By default, this is false.

Here is a an example of running the docker daemon with configuration options:

$ docker daemon -D --tls=true --tlscert=/var/docker/server.pem --tlskey=/var/docker/serverkey.pem -H tcp://192.168.59.3:2376

These options :

Enable -D (debug) mode
Set tls to true with the server certificate and key specified using --tlscert and --tlskey respectively
Listen for connections on tcp://192.168.59.3:2376

The command line reference has the complete list of daemon flags with explanations.

Ubuntu

As of 14.04, Ubuntu uses Upstart as a process manager. By default, Upstart jobs are located in /etc/init and the docker Upstart job can be found at /etc/init/docker.conf.

After successfully installing Docker for Ubuntu, you can check the running status using Upstart in this way:

$ sudo status docker

docker start/running, process 989

Running Docker

You can start/stop/restart the docker daemon using

$ sudo start docker

$ sudo stop docker

$ sudo restart docker

Configuring Docker

You configure the docker daemon in the /etc/default/docker file on your system. You do this by specifying values in a DOCKER_OPTS variable.

To configure Docker options:

Log into your host as a user with sudo or root privileges.
If you don't have one, create the /etc/default/docker file on your host. Depending on how you installed Docker, you may already have this file.
Open the file with your favorite editor.
```
$ sudo vi /etc/default/docker
```
Add a DOCKER_OPTS variable with the following options. These options are appended to the docker daemon's run command.

    DOCKER_OPTS="-D --tls=true --tlscert=/var/docker/server.pem --tlskey=/var/docker/serverkey.pem -H tcp://192.168.59.3:2376"

These options :

Enable -D (debug) mode
Set tls to true with the server certificate and key specified using --tlscert and --tlskey respectively
Listen for connections on tcp://192.168.59.3:2376

The command line reference has the complete list of daemon flags with explanations.

Save and close the file.
Restart the docker daemon.
```
$ sudo restart docker
```
Verify that the docker daemon is running as specified with the ps command.
```
$ ps aux | grep docker | grep -v grep
```

Logs

By default logs for Upstart jobs are located in /var/log/upstart and the logs for docker daemon can be located at /var/log/upstart/docker.log

$ tail -f /var/log/upstart/docker.log
INFO[0000] Loading containers: done.
INFO[0000] docker daemon: 1.6.0 4749651; execdriver: native-0.2; graphdriver: aufs
INFO[0000] +job acceptconnections()
INFO[0000] -job acceptconnections() = OK (0)
INFO[0000] Daemon has completed initialization

CentOS / Red Hat Enterprise Linux / Fedora

As of 7.x, CentOS and RHEL use systemd as the process manager. As of 21, Fedora uses systemd as its process manager.

After successfully installing Docker for CentOS/[Red Hat Enterprise Linux] (/installation/rhel/)/Fedora, you can check the running status in this way:

$ sudo systemctl status docker

Running Docker

You can start/stop/restart the docker daemon using

$ sudo systemctl start docker

$ sudo systemctl stop docker

$ sudo systemctl restart docker

If you want Docker to start at boot, you should also:

$ sudo systemctl enable docker

Configuring Docker

You configure the docker daemon in the /etc/sysconfig/docker file on your host. You do this by specifying values in a variable. For CentOS 7.x and RHEL 7.x, the name of the variable is OPTIONS and for CentOS 6.x and RHEL 6.x, the name of the variable is other_args. For this section, we will use CentOS 7.x as an example to configure the docker daemon.

By default, systemd services are located either in /etc/systemd/service, /lib/systemd/system or /usr/lib/systemd/system. The docker.service file can be found in either of these three directories depending on your host.

To configure Docker options:

Log into your host as a user with sudo or root privileges.
If you don't have one, create the /etc/sysconfig/docker file on your host. Depending on how you installed Docker, you may already have this file.
Open the file with your favorite editor.
```
$ sudo vi /etc/sysconfig/docker
```
Add a OPTIONS variable with the following options. These options are appended to the command that starts the docker daemon.

    OPTIONS="-D --tls=true --tlscert=/var/docker/server.pem --tlskey=/var/docker/serverkey.pem -H tcp://192.168.59.3:2376"

These options :

Enable -D (debug) mode
Set tls to true with the server certificate and key specified using --tlscert and --tlskey respectively
Listen for connections on tcp://192.168.59.3:2376

The command line reference has the complete list of daemon flags with explanations.

Save and close the file.
Restart the docker daemon.
```
$ sudo service docker restart
```
Verify that the docker daemon is running as specified with the ps command.
```
$ ps aux | grep docker | grep -v grep
```

Logs

systemd has its own logging system called the journal. The logs for the docker daemon can be viewed using journalctl -u docker

$ sudo journalctl -u docker
May 06 00:22:05 localhost.localdomain systemd[1]: Starting Docker Application Container Engine...
May 06 00:22:05 localhost.localdomain docker[2495]: time="2015-05-06T00:22:05Z" level="info" msg="+job serveapi(unix:///var/run/docker.sock)"
May 06 00:22:05 localhost.localdomain docker[2495]: time="2015-05-06T00:22:05Z" level="info" msg="Listening for HTTP on unix (/var/run/docker.sock)"
May 06 00:22:06 localhost.localdomain docker[2495]: time="2015-05-06T00:22:06Z" level="info" msg="+job init_networkdriver()"
May 06 00:22:06 localhost.localdomain docker[2495]: time="2015-05-06T00:22:06Z" level="info" msg="-job init_networkdriver() = OK (0)"
May 06 00:22:06 localhost.localdomain docker[2495]: time="2015-05-06T00:22:06Z" level="info" msg="Loading containers: start."
May 06 00:22:06 localhost.localdomain docker[2495]: time="2015-05-06T00:22:06Z" level="info" msg="Loading containers: done."
May 06 00:22:06 localhost.localdomain docker[2495]: time="2015-05-06T00:22:06Z" level="info" msg="docker daemon: 1.5.0-dev fc0329b/1.5.0; execdriver: native-0.2; graphdriver: devicemapper"
May 06 00:22:06 localhost.localdomain docker[2495]: time="2015-05-06T00:22:06Z" level="info" msg="+job acceptconnections()"
May 06 00:22:06 localhost.localdomain docker[2495]: time="2015-05-06T00:22:06Z" level="info" msg="-job acceptconnections() = OK (0)"

Note: Using and configuring journal is an advanced topic and is beyond the scope of this article.