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# 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](/reference/commandline/cli/#daemon) 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](/installation/ubuntulinux/), 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: 1. Log into your host as a user with `sudo` or `root` privileges. 2. 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. 3. Open the file with your favorite editor. ``` $ sudo vi /etc/default/docker ``` 4. 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](/reference/commandline/cli/#daemon) with explanations. 5. Save and close the file. 6. Restart the `docker` daemon. ``` $ sudo restart docker ``` 7. 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](/installation/centos/)/[Red Hat Enterprise Linux] (/installation/rhel/)/[Fedora](/installation/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: 1. Log into your host as a user with `sudo` or `root` privileges. 2. 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. 3. Open the file with your favorite editor. ``` $ sudo vi /etc/sysconfig/docker ``` 4. 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](/reference/commandline/cli/#daemon) with explanations. 5. Save and close the file. 6. Restart the `docker` daemon. ``` $ sudo service docker restart ``` 7. 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._