I got this warning message while building Docker images and trying to start rsyslog inside Docker :
rsyslogd: imklog: cannot open kernel log (/proc/kmsg): Operation not permitted. rsyslogd: activation of module imklog failed
It seems that Unpriviledged cotainers do not have access to kernel log for security reasons. Despite this warning messages, rsyslog running as usual, but if you wish to make the warning dissapear, try to run Docker with –privileged parameter as below :
docker build --no-cache -t ubuntu-rsyslog .
docker run -it --privileged -h ub-syslog.vavai.net ubuntu-rsyslog