How to map volume for Jenkins in Dockers

tl;dr: You dont need add user jenkins with id 1000 on your host, the chown should be enough.

Privilege mismatch is a common problem you often get when using bind mounts. The user running a process inside a container does not match the bind-mount privileges it tries to access.

You can try to run the container as the host user that is allowed to access the bind mount, i.e. as the current host user docker run --user $(id -u):$(id -g) ...

Then again there might be a specific user set in the image to run a process and this trick does not work. If you choose to keep using bind mounts you can change the permissions on the bind mount like you already did, i.e. chown -R 1000:1000 .. You dont need that user on your host system, it should still work, it will just show as user 1000 with gid 1000 on the host without a named user attached.

I suggest to get used to use named mounts instead of bind mounts, it solves alot of the troubles you get with bind mounts.

I did some more RnD and tried following:

I ran the following command

docker volume create jenkins_volume

This creates a volume jenkins_volume in following directory

var/lib/docker/volumes

If i do ll, i get the following details

drwxr-xr-x. 3 root root 4096 Jul 26 07:51 jenkins_volume

i.e. the user and group is root.

Now if i try to run this command it works fine.

docker run -p 8080:8080 -p 50000:50000 -v jenkins_volume:/var/jenkins_home jenkins/jenkins:lts

Although I am not clear to me why earlier it was not working (as in the original question), even when the id and group was root:root for /var/jenkins_home.

May be someone shed more light on this, but for now it am able to make progess.

Thanks.

I also had this problem and I will use different directory paths to avoid ambigiouty in this answer. E.g. -v /var/host/jenkins_home:/var/jenkins_home

First I would like to reproduce the error and create the directory on my host with sudo -u root mkdir -p /var/host/jenkins_home. Since the directory is created by root only root has permission to access it.

$ ls -al /var/host/jenkins_home/
total 8
drwxr-xr-x 2 root root 4096 Jul 27 03:54 .
drwxr-xr-x 3 root root 4096 Jul 27 03:54 ..

When I start jenkins now I will get the same error like you

$ docker run -p 8080:8080 -p 50000:50000 -v /var/host/jenkins_home:/var/jenkins_home jenkins/jenkins:lts
Can not write to /var/jenkins_home/copy_reference_file.log. Wrong volume permissions?
touch: cannot touch '/var/jenkins_home/copy_reference_file.log': Permission denied

To fix this problem you must change the permissions on the host filesystem so that uid 1000 and gid 1000 has access to /var/host/jenkins_home.

sudo chown -R 1000:1000 /var/host/jenkins_home/

If I start jenkins now it will work:

$ docker run -p 8080:8080 -p 50000:50000 -v /var/host/jenkins_home:/var/jenkins_home jenkins/jenkins:lts
Running from: /usr/share/jenkins/jenkins.war webroot: EnvVars.masterEnvVars.get("JENKINS_HOME")
2020-07-27 03:51:36.430+0000 [id=1]     INFO  org.eclipse.jetty.util.log.Log#initialized: Logging initialized @441ms to org.eclipse.jetty.util.log.JavaUtilLog
2020-07-27 03:51:36.577+0000 [id=1]     INFO  winstone.Logger#logInternal: Beginning extraction from war file

When working with docker you should think in uid and gid and not in usernames, because they can differ and lead to confusion.

E.g. on my host machine the uid 1000 is my user rene

 $ id -un 1000
 rene

But in the container it is jenkins:

 $ docker exec <CONTAINER_NAME> id -un 1000
 jenkins

EDIT

I still get same error

Check the permissions in the container

docker run --rm -v /var/host/jenkins_home:/var/jenkins_home jenkins/jenkins:lts ls -al /var/jenkins_home

it should show you that jenkins is the owner and group of /var/jenkins_home

total 12
drwxr-xr-x 2 jenkins jenkins 4096 Jul 27 04:56 .
drwxr-xr-x 1 root    root    4096 Jul 15 14:56 ..
-rw-r--r-- 1 jenkins jenkins  100 Jul 27 04:56 copy_reference_file.log

EDIT

Yes. I am running docker inside a VM, right. And the VM host is also a linux. I am new to dockers, so did not understand much of what you said here. Can you please elaborate.

So you have the following setup:

+-------------------------------------------------------------------------------+
+                                VM  Host                                       | 
+-------------------------------------------------------------------------------+
|                                                                               |
|                           +-------------------------------------------------+ |
| /                         |           VM (Docker Host)                      | |
| +- var                    +-------------------------------------------------+ |
|    +- ...                 | /                      +-----------------------+| |
|                           | +- var                 |   container jenkins   || |
|                           |    +- host             +-----------------------+| |
|                           |       + -jenkins_home  |/                      || |
|                           | /                      |+- var                 || |
|                           |                        |   +- jenkins_home     || |
|                           |                        +-----------------------+| |
|                           +-------------------------------------------------+ |
+-------------------------------------------------------------------------------+

Please ensure that you run the commands on the docker host (the VM). Keep in mind that the docker host file system is different from your local (VM Host).