CODEWITHSUNDEEP
dockersysctl
neorus
neorus

Reputation: 494

Cannot run sysctl command in Dockerfile

I'm trying to make my first dockerfile(I'm new to this), and I need the system to run the command sysctl -w kernel.randomize_va_space=0 (its an lab env.), but I get the error:

sysctl: setting key "kernel.randomize_va_space": Read-only file system

Whenever I try to build the dockerfile, any suggestion how to get this around ?

FROM avatao/lesp:ubuntu-14.04

USER root

COPY ./solvable/ /

RUN sysctl -w kernel.randomize_va_space=0

VOLUME ["/tmp"]

EXPOSE 2222

WORKDIR /home/user/

USER user

CMD ["/usr/sbin/sshd", "-Df", "/etc/ssh/sshd_config_user"]

Upvotes: 27

Views: 49454

Answers (3)

ahmed elouadrhiri
ahmed elouadrhiri

Reputation: 1

Run your container using the following:

docker run --rm -it --privileged myapp:1.0 /bin/bash

Then you will be able to execute your Dockerfile without any problem.

Upvotes: 0

David Maze
David Maze

Reputation: 159750

Since Docker containers share the host system's kernel and its settings, a Docker container usually can't run sysctl at all. (You especially can't disable security-critical settings like this one.) You can set a limited number of sysctls on a container-local basis with docker run --sysctl, but the one you mention isn't one of these.

Furthermore, you also can't force changes like this in a Dockerfile. A Docker image only contains a filesystem and some associated metadata, and not any running processes or host-system settings. Even if this RUN sysctl worked, if you rebooted your system and then launched a container from the image, that setting would be lost.

Given what you've shown in this Dockerfile – customized Linux kernel settings, no specific application running, an open-ended ssh daemon as the container process – you might consider whether a virtual machine fits your needs better. You can use a tool like Packer to reproducibly build a VM image in much the same way a Dockerfile builds a Docker image. Since a VM does have an isolated kernel, you can run that sysctl command there and it will work, maybe via normal full-Linux-installation methods like an /etc/sysctl.conf file.

Upvotes: 31

Debosmit Ray
Debosmit Ray

Reputation: 5413

This is expected since docker restricts access to /proc and /sys (for security). Fundamentally, in order to achieve what you are trying, you need to either give the user CAP_SYS_ADMIN or run in privileged mode, neither of which is allowed during build, see {issue}.

Currently, if you can have those things run after the container is running, then you can use either --cap-add=SYS_ADMIN or --privileged flag. Ideally, these aren't things we would do in a production system, but you seem to be running in a lab setup. If doing it at the run stage, I would recommend first trying the --sysctl flag, but that only supports a subset of command and I'm not sure if it will let you modify kernel settings.

Upvotes: 8

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