Docker build: read-only file system

Question

I'm using a Dockerfile to build my image and I have a command in there that says:

RUN sysctl -w net.ipv4.route.flush=1

but it fails to build the image with the following error:

Step 20 : RUN sysctl -w net.ipv4.route.flush=1
 ---> Running in 4d7302b56c53
sysctl: setting key "net.ipv4.route.flush": Read-only file system

Orthopedic

Answer 1

For security reasons, you need to be in privileged mode for this operation. It is not currently possible to use a Dockerfile with the privileged mode.

$> docker run ubuntu sysctl -w net.ipv4.route.flush=1 && echo ok || echo ko
sysctl: setting key "net.ipv4.route.flush": Read-only file system
ko
$> docker run --privileged ubuntu sysctl -w net.ipv4.route.flush=1 && echo ok || echo ko
ok

Why do you need to do this at build time?

Janel

This affect the host, so if you are doing it as buildtime, it won't be applied the the host running the actual container. – Janel

I need it for mine to override Redis and add vm.overcommit_memory=1 to sysctl.conf or call sysctl -w vm.overcommit_memory=1 so fix a warning from redis to guard check saving when memory is low. – Teyde

Answer 2

This may not apply to your exact situation, but I was receiving read-only file system notices frequently when trying to do a number of operations involving writes:

• docker build
• docker rmi
• etc.

In my case, I was able to solve just by stopping and starting boot2docker:

$ bootdocker down
$ bootdocker up

Donation

Answer 3

Late to the party, but I kept getting this error while running docker build. Turns out my machine just ran out of storage space! Rebooting and deleting all my temp files fixed it.

Coranto