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 docker daemon
command. 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 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.
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, 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.
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
orroot
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 thedocker
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 theps
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/Red Hat Enterprise Linux/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
For CentOS 7.x and RHEL 7.x you can control and configure Docker with systemd.
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:
Log into your host as a user with
sudo
orroot
privileges.-
Create the
/etc/systemd/system/docker.service.d
directory.$ sudo mkdir /etc/systemd/system/docker.service.d
Create a
/etc/systemd/system/docker.service.d/docker.conf
file.-
Open the file with your favorite editor.
$ sudo vi /etc/systemd/system/docker.service.d/docker.conf
Override the
ExecStart
configuration from yourdocker.service
file to customize thedocker
daemon. To modify theExecStart
configuration you have to specify an empty configuration followed by a new one as follows:
[Service] ExecStart= ExecStart=/usr/bin/docker daemon -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 with explanations.
Save and close the file.
-
Flush changes.
$ sudo systemctl daemon-reload
-
Restart the
docker
daemon.$ sudo systemctl restart docker
-
Verify that the
docker
daemon is running as specified with theps
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.
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