I was upgrading my Slackware systems to keep them up with slackware-current, and while a lowly user, I typed "dmesg". I've done this plenty of times before and got the most recent log messages, or after a fresh boot - the bootup messages. Not this time. Instead I got
klogctl: Operation not permitted
Something has changed and I don't know when it changed.
So I added this to my rc.local file for future boots, and ran it manually as root for immediate effect and all is well.
echo 0 > /proc/sys/kernel/dmesg_restrict