Supported tags and respective
CentOS Linux is a community-supported distribution derived from sources freely provided to the public by Red Hat for Red Hat Enterprise Linux (RHEL). As such, CentOS Linux aims to be functionally compatible with RHEL. The CentOS Project mainly changes packages to remove upstream vendor branding and artwork. CentOS Linux is no-cost and free to redistribute. Each CentOS Linux version is maintained for up to 10 years (by means of security updates -- the duration of the support interval by Red Hat has varied over time with respect to Sources released). A new CentOS Linux version is released approximately every 2 years and each CentOS Linux version is periodically updated (roughly every 6 months) to support newer hardware. This results in a secure, low-maintenance, reliable, predictable, and reproducible Linux environment.
CentOS image documentation
centos:latest tag is always the most recent version currently available.
The CentOS Project offers regularly updated images for all active releases. These images will be updated monthly or as needed for emergency fixes. These rolling updates are tagged with the major version number only. For example:
docker pull centos:6 or
docker pull centos:7
Additionally, images with minor version tags that correspond to install media are also offered. These images DO NOT recieve updates as they are intended to match installation iso contents. If you choose to use these images it is highly recommended that you include
RUN yum -y update && yum clean all in your Dockerfile, or otherwise address any potential security concerns. To use these images, please specify the minor version tag:
docker pull centos:5.11 or
docker pull centos:6.6
By default, the CentOS containers are built using yum's
nodocs option, which helps reduce the size of the image. If you install a package and discover files missing, please comment out the line
/etc/yum.conf and reinstall your package.
Currently, systemd in CentOS 7 has been removed and replaced with a
fakesystemd package for dependency resolution. This is due to systemd requiring the
CAP_SYS_ADMIN capability, as well as being able to read the host's cgroups. If you wish to replace the fakesystemd package and use systemd normally, please follow the steps below.
Dockerfile for systemd base image
FROM centos:7 MAINTAINER "you"
ENV container docker RUN yum -y swap -- remove fakesystemd -- install systemd systemd-libs RUN yum -y update; yum clean all; \ (cd /lib/systemd/system/sysinit.target.wants/; for i in *; do [ $i == systemd-tmpfiles-setup.service ] || rm -f $i; done); \ rm -f /lib/systemd/system/multi-user.target.wants/*;\ rm -f /etc/systemd/system/*.wants/*;\ rm -f /lib/systemd/system/local-fs.target.wants/*; \ rm -f /lib/systemd/system/sockets.target.wants/*udev*; \ rm -f /lib/systemd/system/sockets.target.wants/*initctl*; \ rm -f /lib/systemd/system/basic.target.wants/*;\ rm -f /lib/systemd/system/anaconda.target.wants/*; VOLUME [ "/sys/fs/cgroup" ] CMD ["/usr/sbin/init"]
This Dockerfile swaps out fakesystemd for the real package, but deletes a number of unit files which might cause issues. From here, you are ready to build your base image.
docker build --rm -t local/c7-systemd .
Example systemd enabled app container
In order to use the systemd enabled base container created above, you will need to create your
Dockerfile similar to the one below.
FROM local/c7-systemd RUN yum -y install httpd; yum clean all; systemctl enable httpd.service EXPOSE 80 CMD ["/usr/sbin/init"]
Build this image:
docker build --rm -t local/c7-systemd-httpd
Running a systemd enabled app container
In order to run a container with systemd, you will need to use the
--privileged option mentioned earlier, as well as mounting the cgroups volumes from the host. Below is an example command that will run the systemd enabled httpd container created earlier.
docker run --privileged -ti -v /sys/fs/cgroup:/sys/fs/cgroup:ro -p 80:80 local/c7-systemd-httpd
This container is running with systemd in a limited context, but it must always be run as a privileged container with the cgroups filesystem mounted.
Supported Docker versions
This image is officially supported on Docker version 1.6.2.
Support for older versions (down to 1.0) is provided on a best-effort basis.
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