Docker run -v /tmp/something doesn't map correctly

I’m trying to mount a directory so that it has the same path on my machine and in the docker image. I’m using a command like: $ docker run -v /tmp/something:/tmp/something myimage . It fails to create the directory locally, but does seem to be mapping something, because if I touch files in /tmp/something in the docker image, it persists if I restart the container with the same command.

tmp on a mac is a symlink to /private/tmp, but if I change the command to do /private/tmp/something then it fails in the same way.

Mapping a directory from my home directory seems to work fine, but I’m hoping to make this work with /tmp.

Any advice?