Docker (Magyar)

Related articles
Linux Containers
Podman
systemd-nspawn
Vagrant
Docker
is a utility to pack, ship and run any application as a lightweight container.
Telepítés
To pull Docker images and run Docker containers, you need the Docker Engine. The Docker Engine includes a daemon to manage the containers, as well as the
docker
CLI frontend.
Install
the
docker
package or, for the development version, the
docker-git
AUR
package. Next
enable/start
docker.service
or
docker.socket
. Note that
docker.service
starts the service on boot, whereas
docker.socket
starts docker on first usage
which can decrease boot times
. Then verify docker's status:
# docker info
Note that starting the docker service may fail if you have an active VPN connection due to IP conflicts between the VPN and Docker's bridge and overlay networks. If this is the case, try disconnecting the VPN before starting the docker service. You may reconnect the VPN immediately afterwards. You can also try to deconflict the networks (see solutions
[1]
or
[2]
).
Next, verify that you can run containers. The following command downloads the latest
Arch Linux image
and uses it to run a Hello World program within a container:
# docker run -it --rm archlinux bash -c "echo hello world"
To remove the downloaded archlinux docker image, see
#Remove Docker and images
.
If you want to be able to run the
docker
CLI command as a non-root user, add your user to the
docker
user group
, re-login and restart
docker.service
.
Warning
Anyone added to the
docker
group is root equivalent because they can use the
docker run --privileged
command to start containers with root privileges. For more information see
[3]
and
[4]
.
If you plan to build container images using Docker, install
docker-buildx
to use the current builder instead of the deprecated legacy builder.
Docker Compose
Docker Compose
is an alternate CLI frontend for the Docker Engine, which specifies properties of containers using a
compose.yaml
YAML
file rather than, for example, a script with
docker run
options. This is useful for setting up reoccuring services that are used often and/or have complex configurations. To use it,
install
docker-compose
.
Docker Desktop
Docker Desktop
is a proprietary desktop application that runs the Docker Engine inside a Linux virtual machine. Additional features such as a Kubernetes cluster and a vulnerability scanner are included. This application is useful for software development teams who develop Docker containers using macOS and Windows. The Linux port of the application is relatively new, and complements Docker's CLI frontends
[5]
.
An experimental package for Arch is provided directly by Docker; see
the manual
for more information. Unfortunately, it contains files which conflict with the
docker-compose
and
docker-buildx
packages, so you will first need to remove them if installed. Alternatively, you can install
docker-desktop
AUR
package that does not conflict with existing packages.
Also, to run
Docker Desktop
you will need to ensure the
Linux system requirements
, including  virtualization support via
KVM
. To see a tray icon under Gnome,
gnome-shell-extension-appindicator
will be needed.
Finally, file sharing support requires mapping user and group ids via
/etc/subuid
and
/etc/subgid
. See the
Docker Desktop For Linux File Sharing instructions
for more details.
Note
Docker Desktop on Linux runs a Virtual Machine (VM) which creates and uses a custom docker context, desktop-linux, on startup. This means images and containers deployed on the Linux Docker Engine (before installation) are not available in Docker Desktop for Linux.
[6]
For more information see
What is the difference between Docker Desktop for Linux and Docker Engine
.
Furthermore, expect degraded performance and higher cpu usage when using Docker Desktop on Linux.
By default, Docker Desktop enables a user-level systemd service that starts the application automatically on boot. Disabling the "Autostart" setting in the Docker Desktop dashboard
does not
prevent this service from starting (linked issue page includes fixes).
Front-ends
DockStation
— A developer-centric application (GUI) for managing projects based on Docker.
https://github.com/DockStation/dockstation
||
dockstation
AUR
[
Hibás hivatkozás
: package not found]
Ducker
— A terminal app for managing docker containers.
https://github.com/robertpsoane/ducker
||
ducker
goManageDocker
— A TUI tool to manage docker objects.
https://github.com/ajayd-san/gomanagedocker
||
gomanagedocker
AUR
Lazydocker
— A simple terminal UI for docker and docker-compose, written in Go with the gocui library.
https://github.com/jesseduffield/lazydocker
||
lazydocker
oxker
— A simple TUI to view and control Docker containers.
https://github.com/mrjackwills/oxker
||
oxker-bin
AUR
Podman Desktop
— Manage Podman and other container engines from a single UI and tray.
https://github.com/containers/podman-desktop
||
podman-desktop
Portainer
— A lightweight docker management UI.
https://github.com/portainer/portainer
||
portainer-bin
AUR
Whaler
— Docker container management designed for Pantheon.
https://github.com/sdv43/whaler
||
whaler-git
AUR
Usage
Docker consists of multiple parts:
The Docker daemon (sometimes also called the Docker Engine), which is a process which runs as
docker.service
. It serves the Docker API and manages Docker containers.
The
docker
CLI command, which allows users to interact with the Docker API via the command line and control the Docker daemon.
Docker containers, which are namespaced processes that are started and managed by the Docker daemon as requested through the Docker API.
Typically, users use Docker by running
docker
CLI commands, which in turn request the Docker daemon to perform actions which in turn result in management of Docker containers. Understanding the relationship between the client (
docker
), server (
docker.service
) and containers is important to successfully administering Docker.
Note that if the Docker daemon stops or restarts, all currently running Docker containers are also stopped or restarted.
Also note that it is possible to send requests to the Docker API and control the Docker daemon without the use of the
docker
CLI command. See
the Docker API developer documentation
for more information.
See
the Docker Getting Started guide
for more usage documentation.
Configuration
The Docker daemon can be configured either through a configuration file at
/etc/docker/daemon.json
or by adding command line flags to the
docker.service
systemd unit. According to the
Docker official documentation
, the configuration file approach is preferred. If you wish to use the command line flags instead, use
systemd drop-in files
to override the
ExecStart
directive in
docker.service
.
For more information about options in
daemon.json
see
dockerd documentation
.
Storage driver
The
storage driver
controls how images and containers are stored and managed on your Docker host. The default
overlay2
driver has good performance for most use cases.
Users of
btrfs
or
ZFS
may use the
btrfs
or
zfs
drivers, each of which take advantage of the unique features of these filesystems. See the
btrfs driver
and
zfs driver
documentation for more information and step-by-step instructions.
Daemon socket
This article or section is out of date.
Reason:
Unauthenticated TCP connections were deprecated in Docker 26 and are scheduled for removal in Docker 27.
(Discuss in
Talk:Docker (Magyar)
)
By default, the Docker daemon serves the Docker API using a
Unix socket
at
/var/run/docker.sock
. This is an appropriate option for most use cases.
It is possible to configure the Daemon to additionally listen on a TCP socket, which can allow remote Docker API access from other computers.
[7]
This can be useful for allowing
docker
commands on a host machine to access the Docker daemon on a Linux virtual machine, such as an Arch virtual machine on a Windows or macOS system.
Warning
The Docker API is unencrypted and unauthenticated by default. Remote TCP access to the Docker daemon is equivalent to unsecured remote root access unless
additional protection using SSH or TLS is also enabled
.
Note that the default
docker.service
file sets the
-H
flag by default, and Docker will not start if an option is present in both the flags and
/etc/docker/daemon.json
file. Therefore, the simplest way to change the socket settings is with a drop-in file, such as the following which adds a TCP socket on port 2376:
/etc/systemd/system/docker.service.d/docker.conf
[Service]
ExecStart=
ExecStart=/usr/bin/dockerd -H unix:///var/run/docker.sock -H tcp://0.0.0.0:2376
Reload
the systemd daemon and
restart
docker.service
to apply changes.
HTTP Proxies
There are two parts to configuring Docker to use an HTTP proxy: Configuring the Docker daemon and configuring Docker containers.
Docker daemon proxy configuration
See
Docker documentation on configuring Docker daemon to use HTTP proxies
.
Docker container proxy configuration
See
Docker documentation on configuring proxies
for information on how to automatically configure proxies for all containers created using the
docker
CLI.
Configuring DNS
See
Docker's DNS documentation
for the documented behavior of DNS within Docker containers and information on customizing DNS configuration. In most cases, the resolvers configured on the host are also configured in the container.
Most DNS resolvers hosted on
127.0.0.0/8
are
not supported
due to conflicts between the container and host network namespaces. Such resolvers are
removed from the container's /etc/resolv.conf
. If this would result in an empty
/etc/resolv.conf
, Google DNS is used instead.
Additionally, a special case is handled if
127.0.0.53
is the only configured nameserver. In this case, Docker assumes the resolver is
systemd-resolved
and uses the upstream DNS resolvers from
/run/systemd/resolve/resolv.conf
.
If you are using a service such as
dnsmasq
to provide a local resolver, consider adding a virtual interface with a link local IP address in the
169.254.0.0/16
block for dnsmasq to bind to instead of
127.0.0.1
to avoid the network namespace conflict.
Images location
By default, docker images are located at
/var/lib/docker
. They can be moved to other partitions, e.g. if you wish to use a dedicated partition or disk for your images. In this example, we will move the images to
/mnt/docker
.
First,
stop
docker.service
, which will also stop all currently running containers and unmount any running images. You may then move the images from
/var/lib/docker
to the target destination, e.g.
cp -r /var/lib/docker /mnt/docker
.
Configure
data-root
in
/etc/docker/daemon.json
:
/etc/docker/daemon.json
{
  "data-root": "/mnt/docker"
}
Restart
docker.service
to apply changes.
Insecure registries
If you decide to use a self signed certificate for your private registries, Docker will refuse to use it until you declare that you trust it. For example, to allow images from a registry hosted at
myregistry.example.com:8443
, configure
insecure-registries
in the
/etc/docker/daemon.json
file:
/etc/docker/daemon.json
{
  "insecure-registries": [
    "my.registry.example.com:8443"
  ]
}
Restart
docker.service
to apply changes.
IPv6
In order to enable IPv6 support in Docker, you will need to do a few things. See
[8]
[
Halott link
2025-03-15—HTTP 404]
and
[9]
for details.
Firstly, enable the
ipv6
setting in
/etc/docker/daemon.json
and set a specific IPv6 subnet. In this case, we will use the private
fd00::/80
subnet. Make sure to use a subnet at least 80 bits as this allows a container's IPv6 to end with the container's MAC address which allows you to mitigate NDP neighbor cache invalidation issues.
/etc/docker/daemon.json
{
  "ipv6": true,
  "fixed-cidr-v6": "fd00::/80"
}
Restart
docker.service
to apply changes.
Finally, to let containers access the host network, you need to resolve routing issues arising from the usage of a private IPv6 subnet. Add the IPv6 NAT in order to actually get some traffic:
# ip6tables -t nat -A POSTROUTING -s fd00::/80 ! -o docker0 -j MASQUERADE
Now Docker should be properly IPv6 enabled. To test it, you can run:
# docker run curlimages/curl curl -v -6 archlinux.org
If you use
firewalld
, you can add the rule like this:
# firewall-cmd --zone=public --add-rich-rule='rule family="ipv6" destination not address="fd00::1/80" source address="fd00::/80" masquerade'
If you use
ufw
, you need to first enable ipv6 forwarding following
Uncomplicated Firewall#Forward policy
. Next you need to edit
/etc/default/ufw
and uncomment the following lines
/etc/ufw/sysctl.conf
net/ipv6/conf/default/forwarding=1
net/ipv6/conf/all/forwarding=1
Then you can add the iptables rule:
# ip6tables -t nat -A POSTROUTING -s fd00::/80 ! -o docker0 -j MASQUERADE
It should be noted that, for docker containers created with
docker-compose
, you may need to set
enable_ipv6: true
in the
networks
part for the corresponding network. Besides, you may need to configure the IPv6 subnet. See
[10]
for details.
User namespace isolation
By default, processes in Docker containers run within the same user namespace as the main
dockerd
daemon, i.e. containers are not isolated by the
user_namespaces(7)
feature. This allows the process within the container to access configured resources on the host according to
Users and groups#Permissions and ownership
. This maximizes compatibility, but poses a security risk if a container privilege escalation or breakout vulnerability is discovered that allows the container to access unintended resources on the host. (One such vulnerability was
published and patched in February 2019
.)
The impact of such a vulnerability can be reduced by enabling
user namespace isolation
. This runs each container in a separate user namespace and maps the UIDs and GIDs inside that user namespace to a different (typically unprivileged) UID/GID range on the host.
Note
The main
dockerd
daemon still runs as
root
on the host. Running Docker in
rootless mode
is a different feature.
Processes in the container are started as the user defined in the
USER
directive in the Dockerfile used to build the image of the container.
All containers are mapped into the same UID/GID range. This preserves the ability to share volumes between containers.
Enabling user namespace isolation has
several limitations
.
Enabling user namespace isolation effectively masks existing image and container layers, as well as other Docker objects in
/var/lib/docker/
, because Docker needs to adjust the ownership of these resources. The upstream documentation recommends to enable this feature on a new Docker installation rather than an existing one.
Configure
userns-remap
in
/etc/docker/daemon.json
.
default
is a special value that will automatically create a user and group named
dockremap
for use with remapping.
/etc/docker/daemon.json
{
  "userns-remap": "default"
}
Configure
/etc/subuid
and
/etc/subgid
with a username/group name, starting UID/GID and UID/GID range size to allocate  to the remap user and group. This example allocates a range of 65536 UIDs and GIDs starting at 165536 to the
dockremap
user and group.
/etc/subuid
dockremap:165536:65536
/etc/subgid
dockremap:165536:65536
Restart
docker.service
to apply changes.
After applying this change, all containers will run in an isolated user namespace by default. The remapping may be partially disabled on specific containers passing the
--userns=host
flag to the
docker
command. See
[11]
for details.
Rootless Docker daemon
Note
Docker rootless relies on the unprivileged user namespaces (
CONFIG_USER_NS_UNPRIVILEGED
). This is enabled by default in
linux
,
linux-lts
, and
linux-zen
kernels. Users of other kernels may need to enable it. This has some security implications, see
Security#Sandboxing applications
for details.
To run the Docker daemon itself as a regular user,
install
the
docker-rootless-extras
AUR
package.
Configure
/etc/subuid
and
/etc/subgid
with a username/group name, starting UID/GID and UID/GID range size to allocate  to the remap user and group.
/etc/subuid
your_username:165536:65536
/etc/subgid
your_username:165536:65536
Enable
the
docker.socket
user unit
: this will result in docker being started using systemd's socket activation.
Finally set docker socket
environment variable
:
$ export DOCKER_HOST=unix://$XDG_RUNTIME_DIR/docker.sock
Enable native overlay diff engine
By default, Docker cannot use the native overlay diff engine on Arch Linux, which makes building Docker images slow. If you frequently build images, configure the native diff engine as described in
[12]
:
/etc/modprobe.d/disable-overlay-redirect-dir.conf
options overlay metacopy=off redirect_dir=off
Then
stop
docker.service
, reload the
overlay
module as follows:
# modprobe -r overlay
# modprobe overlay
You can then
start
docker.service
again.
To verify, run
docker info
and check that
Native Overlay Diff
is
true
.
Images
Arch Linux
The following command pulls the
archlinux
x86_64 image. This is a stripped down version of Arch core without network, etc.
# docker pull archlinux
See also
README.md
.
For a full Arch base, clone the repository from above and build your own image.
$ git clone
https://gitlab.archlinux.org/archlinux/archlinux-docker.git
Make sure that the
devtools
,
fakechroot
and
fakeroot
packages are installed.
To build the base image:
$ make image-base
Alpine Linux
Alpine Linux
is a popular choice for small container images, especially for software compiled as static binaries. The following command pulls the latest Alpine Linux image:
# docker pull alpine
Alpine Linux uses the
musl
libc implementation instead of the
glibc
libc implementation used by most Linux distributions. Because Arch Linux uses glibc, there are a number of functional differences between an Arch Linux host and an Alpine Linux container that can impact the performance and correctness of software. A list of these differences is documented
here
.
Note that dynamically linked software built on Arch Linux (or any other system using glibc) may have bugs and performance problems when run on Alpine Linux (or any other system using a different libc). See
[13]
,
[14]
and
[15]
for examples.
Debian
The following command pulls the latest
debian
image:
# docker pull debian
See the Docker Hub page for a full list of available tags, including both standard and slim versions for each Debian release.
Distroless
Google maintains
distroless images
which are minimal images without OS components such as package managers or shells, resulting in very small images for packaging software.
See the GitHub README for a list of images and instructions on their use with various programming languages.
Tips and tricks
Get the IP address of a running container
To grab the IP address of a running container:
$ docker inspect --format='{{range .NetworkSettings.Networks}}{{.IPAddress}}{{end}}' <container-name OR id>
172.17.0.37
For each running container, the name and corresponding IP address can be listed for use in
/etc/hosts
:
#!/usr/bin/env sh
for ID in $(docker ps -q | awk '{print $1}'); do
    IP=$(docker inspect --format="{{range .NetworkSettings.Networks}}{{.IPAddress}}{{end}}" "$ID")
    NAME=$(docker ps | grep "$ID" | awk '{print $NF}')
    printf "%s %s\n" "$IP" "$NAME"
done
Run graphical programs inside a container
This section describes the necessary steps to allow graphical programs (including those that rely on OpenGL or Vulkan) to run on the host's X server.
First, the correct drivers, compatible with the
host's
graphics hardware, need to be installed inside the container. The installation procedure depends on the type of the container, but for containers based on Arch Linux images, refer to
OpenGL#Installation
and
Vulkan#Installation
for packages specific to your hardware.
Next, the container must be granted access to the host's X server. In a single-user environment, this can easily be done by running
Xhost
on the host system, which adds non-network local connections to the access control list:
$ xhost +local:
Lastly, the following parameters need to be passed to
docker run
:
-e "DISPLAY=$DISPLAY"
sets the environment variable
DISPLAY
within the container to the host's display;
--mount type=bind,src=/tmp/.X11-unix,dst=/tmp/.X11-unix
mounts the host's X server sockets inside the container under the same path;
--device=/dev/dri:/dev/dri
gives the container access to
Direct Rendering Infrastructure
devices on the host.
To confirm that everything is set up correctly, run
glxgears
from the package
mesa-utils
, or
vkcube
from the package
vulkan-tools
in the container.
Start Docker Compose projects on boot
The factual accuracy of this article or section is disputed.
Reason:
This is not necessary with
restart: always
in the
compose.yml
.
[16]
(Discuss in
Talk:Docker (Magyar)#"Start Docker Compose projects on boot" Spurious?
)
First, create a template
unit
for Docker Compose which is parameterized by the name of the service (see
systemd.service(5) § SERVICE TEMPLATES
):
/etc/systemd/system/docker-compose@.service
[Unit]
Description=%i service with docker compose
Requires=docker.service
After=docker.service

[Service]
WorkingDirectory=/opt/%i
ExecStartPre=-/usr/bin/docker compose pull
ExecStart=/usr/bin/docker compose up --remove-orphans
ExecStop=/usr/bin/docker compose down
ExecReload=/usr/bin/docker compose pull
ExecReload=/usr/bin/docker compose up --remove-orphans

[Install]
WantedBy=multi-user.target
Then, for each service you would like to run, set up a directory with the Compose file and any other required files (such as
.env
files) at
/opt/
project_name
.
[17]
Then,
enable/start
docker-compose@
project_name
.service
.
Using buildx for cross-compiling
The
buildx CLI plugin
makes use of the new
BuildKit building toolkit
.
Install
the
docker-buildx
package. The buildx interface supports building multi-platform images, including architectures other than that of the host.
QEMU is required to cross-compile images. To setup the static build of QEMU within Docker, see the usage information for the
multiarch/qemu-user-static
image. Otherwise, to setup QEMU on the host system for use with Docker, see
QEMU#Chrooting into arm/arm64 environment from x86_64
. In either case, your system will be configured for user-mode emulation of the guest architecture.
$ docker buildx ls
NAME/NODE DRIVER/ENDPOINT STATUS  PLATFORMS
default * docker                  
  default default         running linux/amd64, linux/386, linux/arm64, linux/riscv64, linux/s390x, linux/arm/v7, linux/arm/v6
Run GPU accelerated Docker containers with NVIDIA GPUs
Starting from Docker version 19.03, NVIDIA GPUs are
natively supported as Docker devices
.
NVIDIA Container Toolkit
is the recommended way of running containers that leverage NVIDIA GPUs.
Install the
nvidia-container-toolkit
package and
restart
docker. You can now run containers that make use of NVIDIA GPUs using the
--gpus
option or by registering the NVIDIA container runtime.
With the --gpus option (recommended)
# docker run --gpus all nvidia/cuda:12.1.1-runtime-ubuntu22.04 nvidia-smi
Specify how many GPUs are enabled inside a container:
# docker run --gpus 2 nvidia/cuda:12.1.1-runtime-ubuntu22.04 nvidia-smi
Specify which GPUs to use:
# docker run --gpus '"device=1,2"' nvidia/cuda:12.1.1-runtime-ubuntu22.04 nvidia-smi
or
# docker run --gpus '"device=UUID-ABCDEF,1"' nvidia/cuda:12.1.1-runtime-ubuntu22.04 nvidia-smi
For more information see
the documentation
and
install guide
.
The factual accuracy of this article or section is disputed.
Reason:
More information on when the following error happens is needed. It should work, see
[18]
[
Halott link
2023-04-23—HTTP 404]
. (Discuss in
Talk:Docker (Magyar)#GPU accelerated Docker Nvidia
)
If, when using the above commands, you receive an error such as
Failed to initialize NVML: Unknown Error
, you can try being more specific in specifying the GPU:
# docker run --gpus all --device /dev/nvidiactl:/dev/nvidiactl --device /dev/nvidia-uvm:/dev/nvidia-uvm --device /dev/nvidia0:/dev/nvidia0 nvidia/cuda:12.1.1-runtime-ubuntu22.04 nvidia-smi
Specify a capability (graphics, compute, ...) for the container (though this is rarely if ever used this way):
# docker run --gpus all,capabilities=utility nvidia/cuda:12.1.1-runtime-ubuntu22.04 nvidia-smi
With NVIDIA container runtime
Register the NVIDIA runtime by editing
/etc/docker/daemon.json
/etc/docker/daemon.json
{
  "runtimes": {
    "nvidia": {
      "path": "/usr/bin/nvidia-container-runtime",
      "runtimeArgs": []
    }
  }
}
and then
restart
docker.
The runtime can also be registered via a command line option to
dockerd
:
# /usr/bin/dockerd --add-runtime=nvidia=/usr/bin/nvidia-container-runtime
Afterwards GPU accelerated containers can be started with
# docker run --runtime=nvidia nvidia/cuda:9.0-base nvidia-smi
See also
README.md
.
Arch Linux image with CUDA
You can use the following
Dockerfile
to build a custom Arch Linux image with CUDA. It uses the
Dockerfile frontend syntax 1.2
to cache pacman packages on the host. The
DOCKER_BUILDKIT=1
environment variable
must be set on the client before building the Docker image.
Dockerfile
# syntax=docker/dockerfile:1.2

FROM archlinux:base-devel

# Install packages
RUN --mount=type=cache,sharing=locked,target=/var/cache/pacman \
    pacman -Syu --noconfirm --needed cuda

# Configure nvidia container runtime
# https://github.com/NVIDIA/nvidia-container-toolkit/tree/main/cmd/nvidia-container-runtime#environment-variables-oci-spec
ENV NVIDIA_VISIBLE_DEVICES=all
ENV NVIDIA_DRIVER_CAPABILITIES=compute,utility
Remove Docker and images
In case you want to remove Docker entirely you can do this by following  the steps below:
Note
Do not just copy paste those commands without making sure you know what you are doing.
Check for running containers:
# docker ps
List all containers running on the host for deletion:
# docker ps -a
Stop a running container:
# docker stop <CONTAINER ID>
Killing still running containers:
# docker kill <CONTAINER ID>
Delete containers listed by ID:
# docker rm <CONTAINER ID>
List all Docker images:
# docker images
Delete images by ID:
# docker rmi <IMAGE ID>
Delete all images, containers, volumes, and networks that are not associated with a container (dangling):
# docker system prune
To additionally remove any stopped containers and all unused images (not just dangling ones), add the -a flag to the command:
# docker system prune -a
Delete all Docker data (purge directory):
# rm -R /var/lib/docker
Troubleshooting
docker0 Bridge gets no IP / no internet access in containers when using systemd-networkd
Docker attempts to enable IP forwarding globally, but by default
systemd-networkd
overrides the global sysctl setting for each defined network profile. Set
IPForward=yes
in the network profile. See
Internet sharing#Enable packet forwarding
for details.
When
systemd-networkd
tries to manage the network interfaces created by Docker, e.g. when you configured
Name=*
or
Type=ether
in the
Match
section, this can lead to connectivity issues. The problem should be solved by matching interfaces more specifically, i.e. avoid using
Name=*
or
Type=ether
or other wildcard that matches an interface managed by Docker. Verify that
networkctl list
reports
unmanaged
in the SETUP column for all networks created by Docker.
Note
You may need to
restart
docker.service
each time you
restart
systemd-networkd.service
or
iptables.service
.
Also be aware that
nftables
may block docker connections by default. Use
nft list ruleset
to check for blocking rules.
nft flush chain inet filter forward
removes all forwarding rules temporarily. Edit
/etc/nftables.conf
to make changes permanent. Remember to
restart
nftables.service
to reload rules from the configuration file. See
[19]
for details about nftables support in Docker.
Default number of allowed processes/threads too low
If you run into error messages like
# e.g. Java
java.lang.OutOfMemoryError: unable to create new native thread
# e.g. C, bash, ...
fork failed: Resource temporarily unavailable
then you might need to adjust the number of processes allowed by systemd.
Edit
the
docker.service
with the following snippet:
[Service]
TasksMax=infinity
For more background, look for
DefaultLimitNPROC
at
systemd-system.conf(5) § OPTIONS
. And for
TasksMax
at
systemd.resource-control(5) § OPTIONS
.
Error initializing graphdriver: devmapper
This article or section is being considered for removal.
Reason:
(1) Removing the data directory is extremely hacky and bad (2) The device mapper has been deprecated per the linked issue (Discuss in
Talk:Docker (Magyar)
)
If
systemctl
fails to start docker and provides an error:
Error starting daemon: error initializing graphdriver: devmapper: Device docker-8:2-915035-pool is not a thin pool
Then, try the following steps to resolve the error. Stop the service, back up
/var/lib/docker/
(if desired), remove the contents of
/var/lib/docker/
, and try to start the service. See
https://github.com/moby/moby/issues/21304
for details.
Failed to create some/path/to/file: No space left on device
If you are getting an error message like this:
ERROR: Failed to create some/path/to/file: No space left on device
when building or running a Docker image, even though you do have enough disk space available, make sure:
Tmpfs
is disabled or has enough memory allocation. Docker might be trying to write files into
/tmp
but fails due to restrictions in memory usage and not disk space.
If you are using
XFS
, you might want to remove the
noquota
mount option from the relevant entries in
/etc/fstab
(usually where
/tmp
and/or
/var/lib/docker
reside). Refer to
Disk quota
for more information, especially if you plan on using and resizing
overlay2
Docker storage driver.
XFS quota mount options (
uquota
,
gquota
,
prjquota
, etc.) fail during re-mount of the file system. To enable quota for root file system, the mount option must be passed to initramfs as a
kernel parameter
rootflags=
. Subsequently, it should not be listed among mount options in
/etc/fstab
for the root (
/
) filesystem.
Note
There are some differences of XFS Quota compared to standard Linux
Disk quota
,
[20]
may be worth reading.
Docker-machine fails to create virtual machines using the virtualbox driver
In case docker-machine fails to create the VM's using the virtualbox driver, with the following:
VBoxManage: error: VBoxNetAdpCtl: Error while adding new interface: failed to open /dev/vboxnetctl: No such file or directory
Simply reload the virtualbox via CLI with
vboxreload
.
Starting Docker breaks KVM bridged networking
The issue is that Docker's scripts add some iptables rules to block forwarding on other interfaces other than its own. This is a
known issue
.
Adjust the solutions below to replace br0 with your own bridge name.
Quickest fix (but turns off all Docker's iptables self-added adjustments, which you may not want):
/etc/docker/daemon.json
{
  "iptables": false
}
If there is already a network bridge configured for KVM, this may be fixable by telling docker about it.  See
[21]
where docker configuration is modified as:
/etc/docker/daemon.json
{
  "bridge": "br0"
}
If the above does not work, or you prefer to solve the issue through iptables directly, or through a manager like UFW, add this:
iptables -I FORWARD -i br0 -o br0 -j ACCEPT
Even more detailed solutions are
here
.
Image pulls from Docker Hub are rate limited
Beginning on November 1st 2020, rate limiting is enabled for downloads from Docker Hub from anonymous and free accounts. See the
rate limit documentation
for more information.
Unauthenticated rate limits are tracked by source IP. Authenticated rate limits are tracked by account.
If you need to exceed the rate limits, you can either
sign up for a paid plan
or mirror the images you need to a different image registry. You can
host your own registry
or use a cloud hosted registry such as
Amazon ECR
,
Google Container Registry
,
Azure Container Registry
or
Quay Container Registry
.
To mirror an image, use the
pull
,
tag
and
push
subcommands of the Docker CLI. For example, to mirror the
1.19.3
tag of the
Nginx
image to a registry hosted at
cr.example.com
:
$ docker pull nginx:1.19.3
$ docker tag nginx:1.19.3 cr.example.com/nginx:1.19.3
$ docker push cr.example.com/nginx:1.19.3
You can then pull or run the image from the mirror:
$ docker pull cr.example.com/nginx:1.19.3
$ docker run cr.example.com/nginx:1.19.3
iptables (legacy): unknown option "--dport"
The factual accuracy of this article or section is disputed.
Reason:
Nftables#Working with Docker
advises to not use
iptables-nft
[
Hibás hivatkozás
: replaced by
iptables
]
. (Discuss in
Talk:Docker (Magyar)
)
If you see this error when running a container, install
iptables-nft
[
Hibás hivatkozás
: replaced by
iptables
]
instead of
iptables
(legacy) and reboot
[22]
.
"Your password will be stored unencrypted" when running docker login
By default
Docker will try to use the
pass
or
secretservice
binaries to store your registry passwords. If they are not found, it will store them in plain text (base64-encoded) in
$HOME/.docker/config.json
and print the following message after successfully logging in:
$ WARNING! Your password will be stored unencrypted in /home/
username
/.docker/config.json.
If you are using a password manager that implements the
Secret Service Freedesktop DBUS API
, like KDE's
kwallet
or GNOME's
gnome-keyring
, you can install the
docker-credential-secretservice
AUR
package to store your passwords in them.
"Could not find an available, non-overlapping IPv4 address pool among the defaults to assign to the network"
Sometimes if you use a lot of Docker projects (ex. using docker-compose) it can happens that you run out of available IPs for Docker containers triggering the error:
Could not find an available, non-overlapping IPv4 address pool among the defaults to assign to the network
As found on
this Docker issue
, the defaults are:
Type
Default Size
Default Pool
local
/16
172.17.0.0/12
local*
/20
192.168.0.0/16
This can be easily fixed increasing the Docker IP space by configuring
default-address-pools
in
/etc/docker/daemon.json
increasing the size value from 16 to 24 on the first IP range, keeping the second one unaltered to avoid ip collision on the local network:
/etc/docker/daemon.json
{
  ...
  "default-address-pools" : [
    {
      "base" : "172.17.0.0/12",
      "size" : 24
    },
    {
      "base" : "192.168.0.0/16",
      "size" : 24
    }
  ]
}
Restart
docker.service
to apply changes.
More details and technical explanations can be found on the following excellent article:
The definitive guide to docker's default-address-pools option
.
Slow golang compilation
Due to a ulimit configuration, building a docker image and its dependances with makepkg is very slow (stuck at "Entering fakeroot environment..." step).
It is related to
[23]
and
[24]
.
You can add
--ulimit "nofile=1024:524288"
to your docker build option or create/edit:
/etc/docker/daemon.json
{
  "default-ulimits": {
    "nofile": {
      "Name": "nofile",
      "Soft": 1024,
      "Hard": 524288
    }
  }
}
See also
Official website
Arch Linux on docs.docker.com
Are Docker containers really secure?
— opensource.com
Awesome Docker
Why A Privileged Container in Docker Is a Bad Idea