app-emulation/libvirt's /etc/logrotate.d/libvirtd.qemu entry has a faulty entry which for literally months has been e-mailing me this on a daily basis: error: error switching euid to 77 and egid to -1: Invalid argument That's it. Nothing about libvirt, logrotate etc. So you can see how it took me a while to find the culprit :) Anyhow, I did, and it is this line of /etc/logrotate.d/libvirtd.qemu: su qemu This should be changed, IIUC, to: su root qemu
libvirtd.qemu does not ship with a "su qemu" line. Did you add this line yourself?