update via ./update.sh centos

centos/README.md

@@ -15,22 +15,102 @@ repo](https://github.com/docker-library/official-images).
 
 # CentOS
 
-CentOS (abbreviated from Community Enterprise Operating System) is a Linux
-distribution that attempts to provide a free, enterprise-class,
-community-supported computing platform which aims to be 100% binary compatible
-with its upstream source, Red Hat Enterprise Linux (RHEL). In January 2014, it
-was announced that CentOS was officially joining forces with Red Hat while
-staying independent from RHEL, under a new CentOS Governing Board.
+CentOS Linux is a community-supported distribution derived from sources
+freely provided to the public by [Red Hat](ftp://ftp.redhat.com/pub/redhat/linux/enterprise/)
+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.
+
+
+> [wiki.centos.org](https://wiki.centos.org/FrontPage)
 
-> [wikipedia.org/wiki/CentOS](https://en.wikipedia.org/wiki/CentOS)
+![logo](https://raw.githubusercontent.com/docker-library/docs/master/centos/logo.png)
 
-This is the official CentOS image, and will be updated on a regular schedule or
-as needed for emergency fixes.
+# CentOS image documentation
 
-The `centos:latest` tag will always point to the most recent version currently
-available, and `centos:centos6` will point to the latest version of the CentOS 6 tree.
+The `centos:latest` tag is always the most recent version currently
+available.
 
-![logo](https://raw.githubusercontent.com/docker-library/docs/master/centos/logo.png)
+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 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:
+
+For example: `docker pull centos:5.11` or `docker pull centos:6.6`
+
+
+# Systemd integration
+
+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" <[email protected]>
+    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