Hi!

I'm trying to get the mail server to run on a raspberry pi.
To achieve this I've modified the Dockerfile here and there e.g. :

• change the base image (because ARM)
• replace the apt installation of the filebeat package with a download from somewhere else. (because ARM)

The current error when I try to build the image is the following:
chown: invalid user: ‘syslog:root’

I get this at at the following Dockerfile instruction:
# Configuring Logs RUN sed -i -r "/^#?compress/c\compress\ncopytruncate" /etc/logrotate.conf && \ mkdir -p /var/log/mail && chown syslog:root /var/log/mail && \

My question is:
Where is this syslog user coming from?

Is this user always present in the original Ubuntu base image or is it (normally) added during one of the earlier Dockerfile instructions?

Thanks in advance

update:
changed the base image to this and the problem was solved.
FROM armv7/armhf-ubuntu:14.04