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aliases = ["/engine/articles/configuring/"]
title = "Configuring and running Docker"
description = "Configuring and running the Docker daemon on various distributions"
keywords = ["docker, daemon, configuration, running,  process managers"]
[menu.main]
parent = "engine_admin"
weight = 3
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<![end-metadata]-->

# 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 `dockerd` command. By default it listens on
the Unix socket `unix:///var/run/docker.sock`

    $ 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)
    ...
    ...

### 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 an example of running the `docker` daemon with configuration options:

    $ dockerd -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/dockerd.md)
with explanations.

### Daemon debugging

As noted above, setting the log level of the daemon to "debug" or enabling debug mode
with `-D` allows the administrator or operator to gain much more knowledge about the
runtime activity of the daemon. If faced with a non-responsive daemon, the administrator
can force a full stack trace of all threads to be added to the daemon log by sending the
`SIGUSR1` signal to the Docker daemon. A common way to send this signal is using the `kill`
command on Linux systems. For example, `kill -USR1 <daemon-pid>` sends the `SIGUSR1`
signal to the daemon process, causing the stack dump to be added to the daemon log.

> **Note:** The log level setting of the daemon must be at least "info" level and above for
> the stack trace to be saved to the logfile. By default the daemon's log level is set to
> "info".

The daemon will continue operating after handling the `SIGUSR1` signal and dumping the stack
traces to the log. The stack traces can be used to determine the state of all goroutines and
threads within the daemon.

## 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/linux/ubuntulinux.md),
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

The instructions below depict configuring Docker on a system that uses `upstart`
as the process manager. As of Ubuntu 15.04, Ubuntu uses `systemd` as its process
manager. For Ubuntu 15.04 and higher, refer to [control and configure Docker with systemd](systemd.md).

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/dockerd.md)
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 commit=1b09a95-unsupported graphdriver=aufs version=1.11.0-dev
    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/linux/centos.md)/[Red Hat Enterprise Linux](../installation/linux/rhel.md)/[Fedora](../installation/linux/fedora.md), 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

For CentOS 7.x and RHEL 7.x you can [control and configure Docker with systemd](systemd.md).

Previously, for CentOS 6.x and RHEL 6.x you would configure the `docker` daemon in
the `/etc/sysconfig/docker` file on your system. You would do this by specifying
values in a `other_args` variable. For a short time in CentOS 7.x and RHEL 7.x you
would specify values in a `OPTIONS` variable. This is no longer recommended in favor
of using systemd directly.

For this section, we will use CentOS 7.x as an example to configure the `docker` daemon.

To configure Docker options:

1. Log into your host as a user with `sudo` or `root` privileges.

2. Create the `/etc/systemd/system/docker.service.d` directory.

    ```
    $ sudo mkdir /etc/systemd/system/docker.service.d
    ```

3. Create a  `/etc/systemd/system/docker.service.d/docker.conf` file.

4. Open the file with your favorite editor.

    ```
    $ sudo vi /etc/systemd/system/docker.service.d/docker.conf
    ```

5. Override the `ExecStart` configuration from your `docker.service` file to customize
the `docker` daemon. To modify the `ExecStart` configuration you have to specify
an empty configuration followed by a new one as follows:

```
[Service]
ExecStart=
ExecStart=/usr/bin/dockerd -H fd:// -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/dockerd.md)
with explanations.

6. Save and close the file.

7. Flush changes.

    ```
    $ sudo systemctl daemon-reload
    ```

8. Restart the `docker` daemon.

    ```
    $ sudo systemctl restart docker
    ```

9. 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 commit=1b09a95-unsupported graphdriver=aufs version=1.11.0-dev"
    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._


### Daemonless Containers

Starting with Docker 1.12 containers can run without Docker or containerd running.  This allows the 
Docker daemon to exit, be upgraded, or recover from a crash without affecting running containers 
on the system.  To enable this functionality you need to add the `--live-restore` flag when
launching `dockerd`.  This will ensure that Docker does not kill containers on graceful shutdown or
on restart leaving the containers running.

While the Docker daemon is down logging will still be captured, however, it will be capped at the kernel's pipe buffer size before the buffer fills up, blocking the process.
Docker will need to be restarted to flush these buffers.
You can modify the kernel's buffer size by changing `/proc/sys/fs/pipe-max-size`.