9.1. Docker containers on VectorLinux

9.1.1. Introduction About Docker

According to the official docker website, docker is an open platform for application developers and system administrators to build, ship, and run distributed applications.

Chances are, if you are reading this document, you know what it is, but just in case, see http://www.docker.com for more information. About this guide

This document will guide you through the process of installing docker on your VectorLinux installation and configuring the system to run docker containers. Due to the fact that there is plenty of documentation on how to use the docker platform all over the internet, I decided to save my fingertips and not cover every aspect of ‘how to use docker’ here. A word or caution

Docker is not supported on |vector_edition| version 7.0 or earlier. It will most likely continue to be supported on future releases, but there are no plans to backport this to earlier versions.

9.1.2. Preparing the host

Before any docker containers can be launched, we need to make some modifications to the host Operating System.

The following packages are needed for docker support.

  1. docker

Search for the package(s) and install them via GSlapt or issue the following command on a terminal:

slapt-get -u
slapt-get -i docker


By default, docker is only available to the root user. If you want to make it available to non-root users, add the user to the docker group via the usermod command. usermod -a -G docker <your_user_login>

As of the time of this writing, the default cgroup configuration will not work for supporting docker, so we need to make some changes to the system. This should be very easy if you follow this procedure and run the following commands on a terminal as root (or copy and paste from here) Create new cgroup hierarchy (VectorLinux 7.1)

For cgroups, docker does not support mounting cgroups on the “all” single hierarchy controller, but rather the indivirual controllers. That means we need to create a new hierarchy to use for cgroup mounting because the default VectorLinux does not have this setup by default in version 7.1.

This can be accomplished by running this command on a terminal:

mkdir -p /cgroup/{cpuset,cpu,cpuacct,memory,devices,freezer,net_cls,blkio} Modify your /etc/fstab (VectorLinux 7.1)

Open your /etc/fstab and add the following lines

# For docker compatibility
cgroup /cgroup/cpuset cgroup rw,relatime,cpuset 0 0
cgroup /cgroup/cpu cgroup rw,relatime,cpu 0 0
cgroup /cgroup/cpuacct cgroup rw,relatime,cpuacct 0 0
cgroup /cgroup/memory cgroup rw,relatime,memory 0 0
cgroup /cgroup/devices cgroup rw,relatime,devices 0 0
cgroup /cgroup/freezer cgroup rw,relatime,freezer 0 0
cgroup /cgroup/net_cls cgroup rw,relatime,net_cls 0 0
cgroup /cgroup/blkio cgroup rw,relatime,blkio 0 0 Control groups config file (VectorLinux 7.1)

Add the following content to your /etc/cgconfig.conf file. If the file does not exist yet, create it with this content.

mount {
cpuset = /cgroup/cpuset;
cpu = /cgroup/cpu;
cpuacct = /cgroup/cpuacct;
memory = /cgroup/memory;
devices = /cgroup/devices;
freezer = /cgroup/freezer;
net_cls = /cgroup/net_cls;
blkio = /cgroup/blkio;
} System init script (VectorLinux 7.1)

One last thing to do is to modify the init system so that it respects the instructions set forth in /etc/fstab. You will need to edit your /etc/rc.d/rc.S file and apply this patch (save as text and apply using patch -Np0 < your_saved_text_file --verbose if you want)

--- rc.S.dist   2014-07-30 13:21:16.000000000 +0000
+++ rc.S        2014-07-30 13:21:48.000000000 +0000
@@ -61,15 +61,15 @@
   /bin/plymouth --show-splash

-# Mount Control Groups filesystem interface:
-if grep -wq cgroup /proc/filesystems ; then
-  if [ -d /sys/fs/cgroup ]; then
-    mount -t cgroup cgroup /sys/fs/cgroup
-  else
-    mkdir -p /dev/cgroup
-    mount -t cgroup cgroup /dev/cgroup
-  fi
+## Mount Control Groups filesystem interface:
+#if grep -wq cgroup /proc/filesystems ; then
+#  if [ -d /sys/fs/cgroup ]; then
+#    mount -t cgroup cgroup /sys/fs/cgroup
+#  else
+#    mkdir -p /dev/cgroup
+#    mount -t cgroup cgroup /dev/cgroup
+#  fi

 # Start file systems
 echoc "Mounting local file systems" cyan Finalizing host configuration

After finishing all the previous steps, you will need to restart your computer to get the right cgroups configuration. Continue to the Testing your setup section after the system restarts.

9.1.3. Testing your setup

At this point, your host operating system should be ready to launch docker containers. Follow these steps to verify your system is ready. Start the docker service daemon

/etc/rc.d/rc.docker start
ps ax |grep docker.pid

That should print a line indicating the docker daemon is running and you should also have a /var/run/docker.pid file with a numeric value in it. Networking

After the docker daemon starts, it will create its own network bridge (typically labeled docker0). You can verify this by issuing the ifconfig command on a terminal. The output should display a docker0 entry.

If both of these tests passed, then you are ready to use docker on your VectorLinux installation.

9.1.4. Using Docker

Since there is plenty of documentation out there on how to use docker, I will not waste my breath trying to cover that aspect in depth. This will just be a quick guide on how to download an image, create a container from it and launch a shell inside it. Download an OS image

The docker image repository has lots and lots of images to choose from. For this example, we will be using a slackware64-14.1 image hosted at the public image repository. To see the complete listing issue docker search <term> to search for any distro image that interests you.

docker pull vbatts/slackware

That will download the slackware image and copy it to your local filesystem for docker to use. Run a docker container

After the vbatts/slackware container has been downloaded, you are ready to launch a container using it. To start it issue the following command.

docker run -t -i vbatts/slackware /bin/bash

That will give you a new shell prompt with a very bare slackware setup. Official VectorLinux image

As of this writing, VectorLinux does not yet have an official image on the docker public image repository. A test image has been prepared and uploaded to our public package repository for testing purposes. Keep in mind this is barely getting implemented, so it is possible that the image will change if required later. It is also possible that these images will be available from the docker public image repository later too. To import the testing VectorLinux image, open a terminal and issue the following commands

First download an image.

Then, import the downloaded image into your docker images collection. For this example we will assume you downloaded the 32-bit docker image for VectorLinux 7.1. File name is VL-7.1-BB-FINAL_vlbb-docker.tar.xz

cat VL-7.1-BB-FINAL_vlbb-docker.tar.xz | docker import - vector:7.1-bb

After downloading and importing the image, issue docker images and you should see a line displaying the newly imported image at the top of the listing.

vector 7.1-bb 154ad... about.. 69.36 MB

After the image is imported, you may run it as usual.

docker run -ti vector:7.1-bb /bin/bash


See docker help run for more information on all arguments available to the docker run command. You can also issue docker help for more help on all other docker operations.