To prevent this, let’s generate a new caddy container again but this time once that restarts when the Docker host, Ubuntu in this case, restarts. Stop and remove all running containers. # stop and remove ALL currently running containers sudo docker container stop $(sudo docker ps -q) sudo docker container prune.
- Beginning with Ubuntu 12.10, it is possible to define hooks to be executed at specific points in a container’s lifetime: Pre-start hooks are run in the host’s namespace before the container ttys, consoles, or mounts are up.
- Mar 22, 2017 Hi, I’m new to docker. So I did run docker run -it ubuntu I did some installations (apache, php, etc) on my container. Now when I start my container it stops right away. No idea how to enter to command line and keep my web server running within that container. While I’m reading a book I would appreciate if you can give me some hints and directions.
- One of glibc, musl libc, uclib or bionic as your C library
- Linux kernel >= 2.6.32
Extra dependencies for lxc-attach:
- Linux kernel >= 3.8
Extra dependencies for unprivileged containers:
- libpam-cgfs configuring your system for unprivileged CGroups operation
- A recent version of shadow including newuidmap and newgidmap
- Linux kernel >= 3.12
- libcap (to allow for capability drops)
- libapparmor (to set a different apparmor profile for the container)
- libselinux (to set a different selinux context for the container)
- libseccomp (to set a seccomp policy for the container)
- libgnutls (for various checksumming)
- liblua (for the LUA binding)
- python3-dev (for the python3 binding)
In most cases, you'll find recent versions of LXC available for your Linux distribution. Either directly in the distribution's package repository or through some backport channel.
For your first LXC experience, we recommend you use a recent supported release, such as a recent bugfix release of LXC 4.0.
If using Ubuntu, we recommend you use Ubuntu 18.04 LTS as your container host. LXC bugfix releases are available directly in the distribution package repository shortly after release and those offer a clean (unpatched) upstream experience.
Ubuntu is also one of the few (if not only) Linux distributions to come by default with everything that's needed for safe, unprivileged LXC containers.
On such an Ubuntu system, installing LXC is as simple as:
Your system will then have all the LXC commands available, all its templates as well as the python3 binding should you want to script LXC.
Unprivileged containers are the safest containers. Those use a map of uid and gid to allocate a range of uids and gids to a container. That means that uid 0 (root) in the container is actually something like uid 100000 outside the container. So should something go very wrong and an attacker manages to escape the container, they'll find themselves with about as many rights as a nobody user.
Unfortunately this also means that the following common operations aren't allowed:
- mounting of most filesystems
- creating device nodes
- any operation against a uid/gid outside of the mapped set
Because of that, most distribution templates simply won't work with those. Instead you should use the 'download' template which will provide you with pre-built images of the distributions that are known to work in such an environment.
The following instructions assume the use of a recent Ubuntu system or an alternate Linux distribution offering a similar experience, i.e., a recent kernel and a recent version of shadow, as well as libpam-cgfs and default uid/gid allocation.
First of all, you need to make sure your user has a uid and gid map defined in /etc/subuid and /etc/subgid. On Ubuntu systems, a default allocation of 65536 uids and gids is given to every new user on the system, so you should already have one. If not, you'll have to use usermod to give yourself one.
Next up is /etc/lxc/lxc-usernet which is used to set network devices quota for unprivileged users. By default, your user isn't allowed to create any network device on the host, to change that, add:
This means that 'your-username' is allowed to create up to 10 veth devices connected to the lxcbr0 bridge.
With that done, the last step is to create an LXC configuration file.
- Create the ~/.config/lxc directory if it doesn't exist.
- Copy /etc/lxc/default.conf to ~/.config/lxc/default.conf
- Append the following two lines to it:
- lxc.idmap = u 0 100000 65536
- lxc.idmap = g 0 100000 65536
Those values should match those found in /etc/subuid and /etc/subgid, the values above are those expected for the first user on a standard Ubuntu system.
Install Ubuntu Container On Docker
Running unprivileged containers as an unprivileged user only works if you delegate a cgroup in advance (the cgroup2 delegation model enforces this restriction, not liblxc). Use the following systemd command to delegate the cgroup:
NOTE: If libpam-cgfs was not installed on the host machine prior to installing LXC, you need to ensure your user belongs to the right cgroups before creating your first container. You can accomplish this by logging out and logging back in, or by rebooting the host machine.
And now, create your first container with:
The download template will show you a list of distributions, versions and architectures to choose from. A good example would be 'ubuntu', 'bionic' (18.04 LTS) and 'i386'.
A few seconds later your container will be created and you can start it with:
You can then confirm its status with either of:
And get a shell inside it with:
Stopping it can be done with:
And finally removing it with:
To run a system-wide unprivileged container (that is, an unprivileged container started by root) you'll need to follow only a subset of the steps above.
Specifically, you need to manually allocate a uid and gid range to root in /etc/subuid and /etc/subgid. And then set that range in /etc/lxc/default.conf using lxc.idmap entries similar to those above.
And that's it. Root doesn't need network devices quota and uses the global configuration file so the other steps don't apply.
Any container you create as root from that point on will be running unprivileged.
Privileged containers are containers created by root and running as root.
Depending on the Linux distribution, they may be protected by some capability dropping, apparmor profiles, selinux context or seccomp policies but ultimately, the processes still run as root and so you should never give access to root inside a privileged container to an untrusted party.
If you still have to create privileged containers, it's quite simple. Simply don't do any of the configuration described above and LXC will create privileged containers.
Will create a new 'privileged-container' privileged container on your system using an image from the download template.
Docker is an application that simplifies the process of managing application processes in containers. Containers let you run your applications in resource-isolated processes. Containers are similar to Virtual Machines, but are much less resource-intensive, as they only need the absolute minimum to run a particular application, and does not require installation of a separate Operating System.
Let’s look at how we can install and run the Docker on our Ubuntu 18.04 from the Command Line, in a few steps.
Step 1: Retrieve and add the GPG Public Keys
Again, similar to other tutorials regarding package installation on Linux, we always need to get the public key for that package so that we know that it is valid. We can then download the required data and install the package securely.
So let’s get the GPG public key for Docker, which is available at the link:
To download the key, we will use the
wget command from the Terminal.
The downloaded key in my case is called
gpg. After the public key is downloaded, add it to the system keys using
Step 2: Verify Key Fingerprint
Now, to verify that we have added the proper key, we need to check the fingerprint for Docker’s key.
Verify that you now have the key with the fingerprint
9DC8 5822 9FC7 DD38 854A E2D8 8D81 803C 0EBF CD88, by searching for the last 8 characters of the fingerprint.
You should get an output similar to the below screenshot.
Step 3: Install Required Packages
To set up the Docker repository, our system must have packages which allow us to download files over
HTTPS. So, you need the below packages, which can be downloaded using
Now that we have the necessary requirements, we can now add the Docker repository to our list of sources.
Step 4: Add the Docker Repository to the Sources List
We need to add the Docker source to our list of sources in the system so that any future updates can occur using that source URL when using
We need to modify
Use any text editor (like nano, vi, etc) and open
/etc/apt/sources.list. I will be using
vi editor to edit the file.
Go to the end of the file, and add this line to ensure that we add the repository source link.
Exit the editor, after saving your changes.
Now, we are ready to update the system and install our package!
Step 5: Install Docker on Ubuntu
Now that we have our sources with us, we are ready to install Docker!
It’s simple. First, we update our system and other critical packages. Then, we fetch and install the latest version of Docker from the source. The version that we will be installing is the Docker Community Edition (
docker-ce), so we then install that using
Ubuntu Container For Gns3
Now, if there aren’t any errors, we will return to our shell prompt, and our install has completed successfully!
Step 6: Verify Docker Installation
If Docker was installed correctly, it would have then automatically started a Docker daemon process. So, we need to use the
systemctl command and check if the docker service has started or not.
If the command works as expected, then you will see an output similar to mine, indicating that the
docker service is active, which means that our installation was indeed successful!
Now, let us now look at how we can configure Docker and run a Docker Container.
Step 7: Execute Docker Commands without sudo
By default, the
docker command can only be run by the root user or by a user in the docker group, which is automatically created during Docker’s installation process. If you attempt to run the
docker command without prefixing it with
sudo or without being in the docker group, you’ll get an output like this:
To avoid typing
sudo for every docker command, add your username to the docker group.
Now, log out and log in again to apply for your user membership successfully on the docker group. Now, there is no need to prefix any docker command using
Step 8: Run a Docker Container
A Docker Container, being similar to a Virtual Machine, also needs an image to work on. There are various images hosted on Docker Hub, Docker’s official website for hosting images. Any image you need can be fetched from this website.
Let us now try to run a simple
hello-world Docker Container, which prints ‘Hello World’ and exits.
1. Fetch the image
To pull the corresponding Docker image, use:
2. Run the container
Now we have the image, using which we can run the Docker container.
To check if we actually have the image, let us list all our Docker images on the system, using
We have the image
hello-world in our system, as expected. Now, let us run the container.
Now, this container will run and print
Hello World, before terminating.
We have thus completed running our first Docker Container!
Similarly, we can fetch and run other interactive Docker Containers as well, thus showing the ease of usage of
docker. To illustrate this, let us show one more example: Installing a Debian image!!
Running a Docker Debian Container
We use the same commands as earlier, using
docker pull debian, to download the image.
Now, to run this container, since this needs an interactive terminal session, we use:
-it option specifies an interactive terminal session (Combining the
-i and the
As you can see, we are using a Debian system inside an Ubuntu OS, without the number of resources that a Virtual Machine uses. The image size is itself only 114 MB. Amazing, isn’t it?
Ubuntu Containers On Mac
In this tutorial, we showed you how we can install Docker on Ubuntu 18.04 from the Terminal, and how we can fetch images and run Docker containers using the
docker command. I hope this tutorial serves you well and clears any doubts regarding Docker installation or running a Docker container on Ubuntu.