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I want to deploy docker on a server, but I want all docker-related data to be in a separate partition from the base system. I have thus mounted said partition at '/srv' and made the following changes, according to the official documentation:

This is my '/usr/lib/systemd/system/docker.service' file:

[Unit]
Description=Docker Application Container Engine
Documentation=http://docs.docker.com
After=network.target docker.socket
Requires=docker.socket

[Service]
Type=notify
EnvironmentFile=-/srv/docker/docker.conf
ExecStart=/usr/bin/docker -d -H fd:// $OPTIONS
LimitNOFILE=1048576
LimitNPROC=1048576

[Install]
Also=docker.socket
WantedBy=multi-user.target

This is the '/srv/docker/docker.conf' file that is referenced inside the 'docker.service' file:

$OPTIONS="--graph /srv/docker --storage btrfs"

The docker daemon starts correctly and also PULLs images. The problem is that it still does not store anything inside the '/srv/docker' directory.

Also, when I run 'ps -aux | grep docker', what I get is this:

root       661  0.4  0.2 351080 17044 ?        Ssl  19:33   0:00 /usr/bin/docker -d -H fd://

The command line stops at 'fd://'. It seems to me that '$OPTIONS' is being overlooked for one reason or another.

Now, is there a problem with the way I reference the files? Is there something else going on here? The reason I am doing all these configuration changes is that I would really like to keep all docker related data under the '/srv/docker/' directory.

Any ideas?

UPDATE 1:

I changed my 'docker.conf' file, as suggested in the answers section. Now:

$OPTIONS="--graph /srv/docker --storage btrfs"

became:

OPTIONS="--graph /srv/docker --storage btrfs"

This had the (unexpected) consequence of the docker daemon not starting. This is the debug message from 'systemctl status docker':

[root@V12 ~]# systemctl status docker ● docker.service - Docker Application Container Engine Loaded: loaded (/usr/lib/systemd/system/docker.service; enabled; vendor preset: disabled) Active: failed (Result: exit-code) since Thu 2015-02-05 20:13:31 EET; 14s ago Docs: http://docs.docker.com Process: 776 ExecStart=/usr/bin/docker -d -H fd:// $OPTIONS (code=exited, status=2) Main PID: 776 (code=exited, status=2)

  • What happens if you alter ExecStart to include the line "--graph /srv/docker --storage btrfs" instead? – Matthew Ife Feb 5 '15 at 15:35
  • @MatthewIfe I tried it and the daemon refuses to start. The debug message says that the 'ExecStart' line is to blame. Also, please take a look at the update I made to the question. – dsljanus Feb 5 '15 at 15:37
  • Does that work if you manually invoke docker on the command line with all the options you want? – Matthew Ife Feb 5 '15 at 15:54
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You have an error in your /srv/docker/docker.conf file.

$OPTIONS="--graph /srv/docker --storage btrfs"

The specification of a variable should not start with a $; the $ should only be used when using the variable later.

Change it to:

OPTIONS="--graph /srv/docker --storage btrfs"
  • Please see my update. – dsljanus Feb 5 '15 at 16:19
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    Well, at least now your environment file works :) – Michael Hampton Feb 5 '15 at 16:30
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    I am so going to put this up for a bounty. – dsljanus Feb 5 '15 at 16:37
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First off I want to thank @MichaelHampton for his answer. It was spot on, and I would have never spotted the typo with the '$' ('OPTIONS=...' instead of '$OPTIONS=...').

Now, the problem was with the command line options. In the docker documentation the argument for changing the storage driver is given as:

--storage btrfs

Keep in mind that this is the docs for version 1.4, which is the version I have. Alas, the correct syntax, as evidenced by 'docker --help' is:

--storage-driver btrfs

So, after making the necessary change, the daemon starts correctly, the images are PULL-ed inside the '/srv/docker' directory, and everything is fine.

The moral is to always be a little mistrustful of official documentations, especially for projects under heavy development, like Docker. Again thanks to all for their contributions.

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Initially I spent quite a bit of time fiddling with the previous upstart/sysv initscript from /etc/init.d/docker and its configuration file /etc/default/docker. It was really strange that it just didn't work no matter what I tried, then eventually I realized that systemd just ignores both of those, since I was using the legacy script directly.

The proposed solution doesn't seem to work 100% on my 15.04 with lxc-docker-1.7.0 installed from the official docker PPA, since the EnvironmentFile seems to be missing from my docker's systemd configuration file.

An option would be to edit it in-place and add it using this command:

sudo systemctl edit docker --full

But this risks to be overridden by the next update, so my solution was to instead create an override, by running

sudo systemctl edit docker

Then I decided to just redefine the ExecStart command in the new configuration override, instead of also adding and referencing a new configuration file under /srv/docker/docker.conf.

[Service]
ExecStart=
ExecStart=/usr/bin/docker -d -H fd:// --storage btrfs

There's no error in the snippet above, for some strange reason that has to do with the way systemd reads its configuration overrides, a value needs to be first defined with an empty value, then reassigned to the new value.

Once I did this the daemon started happily and I was finally able to use it.

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