Docker (CentOS 7 with SYSTEMCTL) : Failed to mount tmpfs & cgroup

Question

(I'm a Docker beginner. Then I followed some tutorials for CentOS-7)

In my CentOS 7.2, I tried to learn Docker by following the steps below.

# docker version

Client:
 Version:      1.10.3
 API version:  1.22
 Go version:   go1.5.3
 Git commit:   20f81dd
 Built:        Thu Mar 10 15:39:25 2016
 OS/Arch:      linux/amd64

Server:
 Version:      1.10.3
 API version:  1.22
 Go version:   go1.5.3
 Git commit:   20f81dd
 Built:        Thu Mar 10 15:39:25 2016
 OS/Arch:      linux/amd64

# docker pull centos:latest
# docker images
centos     latest    778a53015523    12 days ago    196.7 MB

# mkdir ~/docker/centos7-systemd
# cd ~/docker/centos7-systemd
# vi Dockerfile
FROM centos
MAINTAINER "XXXX XXXX" <[email protected]>
ENV container docker
RUN (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"]

# docker build --rm -t local/centos7-systemd .
..
Successfully built 1a9f1c4938b3

# docker images
centos                  latest    778a53015523    12 days ago    196.7 MB
local/centos7-systemd   latest    1a9f1c4938b3    8 seconds ago  196.7 MB

So up to this point, everything (seems) ok.
Now the problem comes when I run:

# docker run -ti -v /sys/fs/cgroup:/sys/fs/cgroup:ro -p 80:80 local/centos7-systemd
Failed to mount tmpfs at /run: Operation not permitted
Failed to mount cgroup at /sys/fs/cgroup/systemd: Operation not permitted
[!!!!!!] Failed to mount API filesystems, freezing.

What does this even mean, and more importantly, what is happening and how can I solve this, please?

Thank you all :)

Answer 1

The more modern approach to this, after Daniel Walsh contributed a series of patches, is this...

docker run -ti --tmpfs /tmp --tmpfs /run -v /sys/fs/cgroup:/sys/fs/cgroup:ro -p 80:80 local/centos7-systemd

Essentially starting in a privileged container is a bad idea for security reasons. Since Daniel contributed patches to make it unnecessary we are able to start without escalating privileges.

While it's true that we should maintain the "single service/process per container" principle in general, some people want to run RedHat supported containers, which means the use of systemd.

See https://developers.redhat.com/blog/2016/09/13/running-systemd-in-a-non-privileged-container/ for more information

To demonstrate a stripped down systemd container, something like this would have an apache and tomcat running; not the single service/process principle, but just an example. You'd obviously need to do more to this image, but this is the basic idea. I think I got this from one of Daniel's posts somewhere, but I don't recall now.

FROM centos:7
ENV container docker
RUN (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/*;
RUN yum -y install httpd tomcat tomcat-javadoc.noarch \
    tomcat-docs-webapp.noarch tomcat-admin-webapps.noarch ; \
    yum clean all
RUN systemctl enable tomcat.service
RUN systemctl enable httpd.service

VOLUME [ "/sys/fs/cgroup" ]
EXPOSE 80 8080
CMD ["/usr/sbin/init"]

docker build -t apache ./
docker run --tmpfs /tmp --tmpfs /run -it -v /sys/fs/cgroup:/sys/fs/cgroup:ro -p 8081:80 -p 8080:8080 --name apache apache

Answer 2

try to run your container in privileged mode:

docker run -ti --privileged=true -v /sys/fs/cgroup:/sys/fs/cgroup:ro -p 80:80 local/centos7-systemd

this should solve your problem

Answer 3

I got the same problem with Docker for Windows (1.12.3)...

$ docker logs bareos
systemd 219 running in system mode. (+PAM +AUDIT +SELINUX +IMA -APPARMOR +SMACK +SYSVINIT +UTMP +LIBCRYPTSETUP +GCRYPT +GNUTLS +ACL +XZ -LZ4 -SECCOMP +BLKID +ELFUTILS +KMOD +IDN)
Detected virtualization docker.
Detected architecture x86-64.

Welcome to CentOS Linux 7 (Core)!

Set hostname to <bareos>.
Failed to install release agent, ignoring: No such file or directory
Failed to create root cgroup hierarchy: No such file or directory
Failed to allocate manager object: No such file or directory
[!!!!!!] Failed to allocate manager object, freezing.

The latest boot2docker doesn't have systemd. We can't have systemd in a Docker container, if the host doesn't have it. Since the important folder for that is /sys/fs/cgroup/systemd.

So finally, I create a default vm in VitualBox based on Alpine Linux and a default docker-machine with the generic driver.