Tag Archives: Fedora

Fedora Developer Portal – how to contribute

The great thing about working at Red Hat is being part of the Fedora community and as a part of this group of enthusiastic people you get close to cool, interesting, awesome, innovative, important... projects. And you get close to them while they are at the beginning and you can influence where they go.

One of those projects is Fedora Developer Portal which will help developers to start their projects on Fedora. It will help you figure out what languages, frameworks, or databases are available in our distribution. How to use Docker, Vagrant or Copr build system to package, distribute and deploy your projects. There is already content ready for you to help you with setting things up for Arduino. Much of other content is in preparations and even more is waiting for you to come and join the project!

My contribution to the project so far has been making it easy for you to contribute. I helped guys with contribution guidelines and I created a Docker image which will let you run the website locally so that you can review your contributions.

This is what you can also find in a README.md for the website project:

$ sudo docker run -it --rm developerportal/devel
[sudo] password for vpavlin: 
Previous HEAD position was 702f2a3... move logo to static directory
Switched to branch 'master'
Your branch is up-to-date with 'origin/master'.
Already up-to-date.
Configuration file: /opt/developerportal/website/_config.yml
/home/dp/.gem/ruby/gems/jekyll-lunr-js-search-0.3.0/lib/jekyll_lunr_js_search/version.rb:3: warning: already initialized constant Jekyll::LunrJsSearch::VERSION
/opt/developerportal/website/_plugins/jekyll_lunr_js_search.rb:245: warning: previous definition of VERSION was here
 Source: /opt/developerportal/website
 Destination: /opt/developerportal/website/_site
 Lunr: Creating search index...
 Build Warning: Layout 'page' requested in content/fedora_features/Fedora23_Self_contained_Changes.md does not exist.
 Build Warning: Layout 'page' requested in content/fedora_features/Fedora23_System_Wide_Changes.md does not exist.
 Lunr: Index ready (lunr.js v0.4.5)
 Auto-regeneration: enabled for '/opt/developerportal/website'
Configuration file: /opt/developerportal/website/_config.yml
 Server address:
 Server running... press ctrl-c to stop.

You can see a server address - that's what you need to copy to your browser to view the page.

Screenshot from 2015-09-02 09-39-51

Now you have the local dev instance running. What if you want to display your changes? First, you clone the content repository.

$ git clone https://github.com/developer-portal/content

Then you will have to modify the run command a bit - specifically, add a volume mount (replace $PWD/content with the path to the cloned content repository):

$ sudo docker run -it --rm -v $PWD/content:/opt/developerportal/website/content developerportal/devel

Ok, now what if you don't want to contribute to content of the portal but rather to help guys making the website awesome? The approach is the same as above. First, you clone the website repository.

$ git clone https://github.com/developer-portal/website

Then you run the container just with the mount for website instead of content.

$ sudo docker run -it --rm -v $PWD/website:/opt/developerportal/website developerportal/devel

Jekyll is used to render the website and it's content and it's set up in the way that whenever you edit any file the website re-renders itself and you can simply refresh the browser when it's finished.

The rest is easy - you change whatever you want, push to your fork on Github, submit a pull request. Once it's reviewed, your changes will appear on the web. Yay!

Ok, my job is done here. Now it's your turn to contribute and promote it further!:)

How to (be a) man on Atomic Host

One major thing missing on the Atomic Host are manual pages. Not a terrible thing - you can always google for them, right? But what if you cannot? Then there is the Fedora Tools Docker image. Try this:

-bash-4.3$ alias man="sudo atomic run vpavlin/fedora-tools man"
-bash-4.3$ man systemd

You should see a manual page for systemd. Thinking about it, that's it. Nothing more you need to now about it. Simple:)


Running git on Atomic Host with Fedora Tools image

I added the Fedora Tools image to Fedora-Dockerfiles repository, as you might know from my earlier post. I'd like to introduce you to one use case for this image - git.

When I started to work more on Docker images, I started using Atomic Host(s) for testing as they boot faster and are easier to set up than classic installations. Problem was to get data in those VMs running Atomic Host as git was not present. That's where I first really appreciated the tools image.

bash-4.3# yum
bash: yum: command not found
bash-4.3# git
bash: git: command not found
bash-4.3# atomic run fedora/tools
[root@localhost /]# cd /host/home/vagrant/
[root@localhost vagrant]# git clone https://github.com/fedora-cloud/Fedora-Dockerfiles
Cloning into 'Fedora-Dockerfiles'...
remote: Counting objects: 2189, done.
remote: Compressing objects: 100% (9/9), done.
remote: Total 2189 (delta 3), reused 0 (delta 0), pack-reused 2180
Receiving objects: 100% (2189/2189), 915.13 KiB | 901.00 KiB/s, done.
Resolving deltas: 100% (1014/1014), done.
Checking connectivity... done.
[root@localhost vagrant]# exit
bash-4.3# ls
Fedora-Dockerfiles sync

It's simple, right? You can see there is neither yum/dnf, nor git on the host, but still, I was able to clone the repository from Github very easily. The important thing to notice is the path I cd'ed to: /host/home/vagrant. You can see /host prefix there. That's where the host's filesystem is mounted and where I can access it and modify it.

You can review the docker run command for the tools image f.e. with this command:

bash-4.3# docker inspect --format='{{.Config.Labels.RUN}}' vpavlin/fedora-tools
docker run -it --name NAME --privileged --ipc=host --net=host --pid=host -e HOST=/host -e NAME=NAME -e IMAGE=IMAGE -v /run:/run -v /var/log:/var/log -v /etc/localtime:/etc/localtime -v /:/host IMAGE

Obviously, you can do more, not just clone the repo - you can run commit, push, checkout or anything else the same way.

Fedora Tools Docker image

I got this request from my colleagues if there is something like Red Hat Atomic Enterprise Tools container image available for Fedora or CentOS. The answers was no, there isn't, thus I started to work on it. I'd like to tell you what it is and why do I invest my time into it.

First of all, Fedora Tools image is meant to be used mostly on Atomic Host as there is no way to install missing tools with yum or dnf. We could create tons of small images each containing a single tool. But that would a) make it hard for users to find all the tools, b) consume more space then a single image if you decide to use many (all...) of them, c) be hard to maintain.

These 3 reasons lead us to create a single image containing big number of tools important to sysadmins, performance analysts, or just users that need man pages on Atomic Host. This image is pretty big (more than 1 GB), but can be pretty useful.

Current version of the Dockerfile can be found in Fedora-Dockerfiles repository. You can find the list of additional packages (to what's already in a base image) starting on line 13.

The basic information on how to use the Fedora Tools Docker image can be found in README file and I hope to provide more how-to's here soon:).

I've set up an automated build as vpavlin/fedora-tools under my namespace on Docker Hub. To try the image, you can do:

atomic run vpavlin/fedora-tools


Taskwarrior in a Docker container

So I heard about great tool - Taskwarrior. Cool, let's try it. Well, sure, but why should I install another bunch of RPMs to my laptop? Not that it matters a lot, but I hate to have my system bloated with unused packages which are installed as dependencies, but stay there when I remove the "root" package. Let's go crazy and create a simple Taskwarrior container.

I started with plain Dockerfile.

FROM fedora
MAINTAINER Vaclav Pavlin <vpavlin@redhat.com>
RUN dnf -y install task
VOLUME /task_data


That was not ideal because the final container missed very important settings - data location. So I added 2 lines which initialized ~/.taskrc and changed the data location to a well known path. I also added man command to the mix so that I can display manual pages for Taskwarrior. Final Dockerfile follows

FROM fedora
MAINTAINER Vaclav Pavlin <vpavlin@redhat.com>
RUN dnf -y install task man
VOLUME /task_data
RUN yes | task || true
RUN sed -i 's#\(data.location=\).*#\1/task_data#' ~/.taskrc

Still pretty simple, isn't it? Now, how to run this image? Just call the following command, there is an image ready for you on Docker Hub:

docker run -it --rm -v $HOME/.task:/task_data vpavlin/task

The command above will start a container which will initialize few files in $HOME/.task directory and print output like this:

[task next]
No matches.

You can try some fancy stuff with Taskwarrior itself now:

Screenshot from 2015-08-18 16-40-32Well, it works. But also is pretty ugly. Let's make the user experience nicer and smoother. You can simply create an alias for docker run command. For example like this one:

$ alias task="docker run -it --rm -v $HOME/.task:/task_data vpavlin/task"
$ task
[task next]

ID Age Project Tag Description Urg 
 1 6s vpavlin.eu blog today This is a test taks for my blog post 1.9

1 task

Then, when you call task, you will get the same output as if Taskwarrior was installed on you machine. Also your data will be stored locally so you don't have to be afraid of losing them when you remove container/image.

I also wrote a simple task function which you can paste in your ~/.bash_aliases file which lets you either use Taskwarrior as with the alias above, or you can do

task CMD man task

Note CMD in the command - that will let the bash function know to run different command than the one specified in Dockerfile - f.e. view the man pages.

I also strongly suggest to set the data location (i.e. the volume mount, or $data_dir variable in the function) to a backed up folder. I, for example, use Dropbox, so that I can access and modify my tasks from any machine (basically just by pulling and running the Docker image).



Delete an Image from Private Docker Registry

Have you ever wondered how to remove repositories/tags from your private Docker registry? It's simple according to Docker registry API specs. So let's try this

yum -y install docker-registry
sudo systemctl start docker-registry
docker pull fedora:21
docker tag fedora:21 localhost:5000/fedora:21 
curl localhost:5000/v1/repositories/fedora/tags/21

You should see an image id printed to your terminal. Now let's delete the image...

$ curl -X DELETE localhost:5000/v1/repositories/fedora/tags/21

To be clear - it does not remove the image/layers data - it just removes the reference from fedora:21 tag to the image id (i.e. data). If there is any other tag referencing the data, they will still be accessible.

Anyway, in some cases it is useful to be able to remove this reference. I run a private registry with 337 images (multiplied by few tags for every image) and I sometimes found myself in a situation where I pushed an image with wrong tag or I just wanted to stop people from pulling a specific image. I wrote a small bash script for these occasions - drrm.sh. The usage is simple

drrm.sh NAME[:TAG]

Which means for our fedora example

$ ./drrm.sh localhost:5000/fedora:21
Do you really want to untag "834629358fe214f210b0ed606fba2c17827d7a46dd74bd3309afc2a103ad0e89"? [y/N]: y
Image library/fedora:21 removed from localhost:5000

Firstly it checks if the image exists, then it asks for confirmation of removal and then it calls the previously shown curl command to delete the reference. I also have a simple "Docker Registry Garbage Collector" under development which goes through the docker-registry directory and moves unreferenced layers away (where you can delete them later). But that's going to be a topic next time:).

Running services with docker and systemd

I have described how to run systemd in a Docker container on Fedora in previous article but didn't give you any "real" example of how to actually use it. I guess you find it easy to figure out your own examples but let me show you mine.

WordPress & MariaDB

I like to use WP and MariaDB as example applications when I give a talk about containers. It's quite simple setup and at the same time uses some nice features of docker (f.e. links or port mapping). If you just want to see my Dockerfiles, please go to this github repository. If want more babbling, read on.

The MariaDB Dockerfile is forked from Fedora-Dockerfiles and I guess it will be "merged" there soon:). First few lines are quite boring - yum update/install. Next line I really like. How to start MariaDB properly..hmm...hey, let's use what packagers came up with - mariadb.service file.

RUN systemctl enable mariadb.service

This really presents the beauty of using systemd inside containers. Single line tells the init that we want to start the service on the container start. Easy, clean, awesome. Then some "stuff" follows. I let it up to you to figure out what it actually does - everybody likes homeworks, right?

You can also check my WordPress Dockerfile in the same repository. It's a bit longer but the most important line for this case is again enablement of the service - in this case httpd.

RUN systemctl enable httpd.service

If you build those two images...

docker build -t vpavlin/mariadb mariadb/
docker build -t vpavlin/wordpress wordpress/

You can run them with these commands

docker run -it --rm -v /sys/fs/cgroup:/sys/fs/cgroup --name mariadb vpavlin/mariadb
docker run -it --rm -v /sys/fs/cgroup:/sys/fs/cgroup -p 80:80 --name wordpress --link mariadb:mariadb vpavlin/wordpress

To describe these commands I'd say: Run a container with stdin and out attached to my tty, volume mount /sys/fs/cgroup for systemd, name containers mariadb and wordpress (respectively) and link mariadb to wordpress (which basically mean tell WP how to connect to mariadb). Oh, and map port 80 of WP container to host's port 80.

When you hit http://localhost in your browser, you should see a WP installation page.

Snímek z 2015-02-24 23:35:53

Any questions?:)

Fedora, docker and systemd

You've heard about systemd, right? The init system wrote (not only) by famous Lennart Poettering which is trying to eat all those nice ancient tools and system parts (just kidding😉 but which also makes live of many system administrator waaaaay easier. You've probably also heard about Docker - the tool which currently leads the world of linux containers (and soon will do the same in Windows world probably). So, where does these 2 projects and programs meet?

Scott Collier asked me to provide him a status where we are with "running systemd in Docker containers" in Fedora and let him know how to actually make it work. If you searched Google before, you've probably found Dan Walsh's article about running systemd inside a container. Some things changed, some (hopefully) will change sooner or later, but I can tell you that it's quite easy now to run services in a Docker container by systemd.

First things first. To be able to run systemd we need few things - cgroup tree, /run and /tmp to be a mountpoint (preferably on tmpfs), environment variable container to be set to "docker", get rid of fstab and mount units, tweak dbus.service a bit and that's it. Some of them are on you, we took care of the rest in Fedora base images.


Well, it's simple - systemd touches /sys/fs/cgroup and expects it to be populated. As kernel won't populate cgroups in container, we need to mount it from the host. Easy, right? Sadly this cannot be done automatically as Docker tries to stay above these distribution specific modifications (which is good..mostly). So you need to add

-v /sys/fs/cgroup:/sys/fs/cgroup:ro

to your docker create/run cmdline.

Temp mounts

We can blame both - systemd and Docker from not being able to solve this for us automatically. We need either that systemd does not require /run and /tmp to be mount points or that Docker provides volumes for them by default. I think I understand both points of view. It's again a distribution specific change for Docker and at the same time it's a sane default for systemd to require to have /tmp and /run really temporary. So how to get around this? Let's add another volume to our image (there is a PR for Docker to do it automatically). Contrary to the cgroup mount, this does not have to lead to any specific location on host. So the command line solution would be

-v /run -v /tmp

or in Dockerfile

VOLUME ["/run", "/tmp"]

Environment variable(s)

There are ways for systemd to figure out where and how it runs. It checks bunch of things and one of them is environment variable $container. It can equal to few things (f.e. lxc) but here we, for obvious reasons, want to have it's value set to docker. So on command line you would need

-e container=docker

or in Dockerfile

ENV container docker

There is another variable systemd can use. It's called $container_uuid and it is used to set the /etc/machine-id. That can be very useful because it for example identifies your container in journald. Wouldn't it be awesome if we could get this set up automatically by Docker daemon when the container is created? There is a (closed) PR on Docker for this.


Docker containers drop sysadmin capability which is good for security but bad for systemd. It tries to do some mounting on start up and it expectedly fails. The easiest way of getting rid of these fails is 1) to remove /etc/fstab and 2) to mask mount units which systemd ships (I've found these in a Fedora base image: dev-hugepages.mount, sys-fs-fuse-connections.mount). Both is done in fedora-base-docker.ks in %post section (which is used to build the base image).


This again has something to do with capabilities. Dbus service tries to change it's OOMScore in unit file which fails. But this time it fails quite badly - sometimes the container dies completely, sometimes systemd says it's logging to fast and freezes, but in all cases the container is basically useless. It should be fixed in latest systemd builds in Fedora, but I still hit this in fedora:21 image. To solve this for your containers, please add this line to your Dockerfile

RUN cp /usr/lib/systemd/system/dbus.service /etc/systemd/system/; sed -i 's/OOMScoreAdjust=-900//' /etc/systemd/system/dbus.service


Ok, now I hopefully convinced you that running your services in containers by systemd is easy. sadly, what you need at the moment is to create another layer over Fedora base image. You can do that with this Dockerfile:

FROM fedora
MAINTAINER Vaclav Pavlin <vpavlin@redhat.com>

RUN yum -y update; yum clean all

RUN systemctl mask systemd-remount-fs.service dev-hugepages.mount sys-fs-fuse-connections.mount systemd-logind.service getty.target console-getty.service
RUN cp /usr/lib/systemd/system/dbus.service /etc/systemd/system/; sed -i 's/OOMScoreAdjust=-900//' /etc/systemd/system/dbus.service

VOLUME ["/sys/fs/cgroup", "/run", "/tmp"]
ENV container=docker

CMD ["/usr/sbin/init"]


Build it for example like this

docker build -t fedora:systemd .

Or use an image I've prepared for you on Docker Hub: vpavlin/fedora:systemd

Following command will do the work:

docker run -it --rm -v /sys/fs/cgroup:/sys/fs/cgroup:ro fedora:systemd

Snímek z 2015-02-24 12:07:15

Some lines will be redundant in the Dockerfile above when F22 will be released so I'll probably update the article when we get there.

By the way, you probably want to continue with next post: Running services with docker and systemd.