Docker build hangs when adding user with a large value of user ID / UID

user_9962007 0
Viewed 83

When trying to build a docker image with a large value of UID, such as 1000123456, docker build repeatedly hangs on the line with RUN useradd.

To reproduce:

$ touch Dockerfile
$ echo FROM ubuntu:latest >> Dockerfile
$ echo RUN useradd -m -s /bin/bash -N -u 1000123456 jovyan >> Dockerfile
$ docker build --tag mirekphd/test-uid .
Sending build context to Docker daemon  2.048kB
Step 1/2 : FROM ubuntu:latest
 ---> d2e4e1f51132
Step 2/2 : RUN useradd -m -s /bin/bash -N -u 1000123456 jovyan
 ---> Running in 04707e01aefc

Any known solutions (to accept) or at least workarounds (to upvote)?

More info

This bug can manifest itself for example when trying to hard-code (for debug only) a UID within the range of values accepted by one of Openshift/OKD namespaces.

As a side-effect of this issue, the build takes up huge amount of disk space (any proposed workarounds should be free of this side-effect):

$ docker system prune -f
Deleted Containers:
04707e01aefcda9ce9840389f1d59821e1ddb7dac535d416f99447e657ec5309
c3fc96209790ee7aa0c2c10bec2459e8ec3dbcc1dc7cfdd0a3e12960a28b9437
1ed4985b3e27eaff6394fd0243713573473ab59c9a82db865e40ebb40a391892

Total reclaimed space: 648.1GB
docker-build dockerfile openshift docker linux
2 Answers

You can use the useradd's --no-log-init option (or shorter: -l):

useradd --no-log-init -m -s /bin/bash -N -u 1000123456 jovyan

The huge files created in the Docker image (/var/log/faillog and /var/log/lastlog) are sparse files. Using --no-log-init avoids creating these files (huge in the case you add a user with a large uid). Why are these files huge?

useradd by default reserves space for all users, so when using (say), uid 10000, it reserves space for 10000 users, even if only user 10000 is used; for this, a sparse-file is created

Source: https://github.com/docker/hub-feedback/issues/2263#issuecomment-1205423533

References (it seems to be a known issue for a long time):

user_78040580

Please, introduce the following instructions:

RUN apt -y update
RUN apt -y install strace
RUN strace useradd -m -s /bin/bash -N -u 123456 jovyan

You can see that useradd exits and docker build terminates as expected.

Now, change UID into 1000123456: useradd terminates as the previous scenario, but docker doesn't.

I suppose may be a bug in the Ubuntu image.

I suggest you to try with another image...

Let me know if it will work.

Regards.

user_4185990
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