"failed to get path uid" - Multipathd Error Message with Non-multipathed Devices

The Problem

At the time starting multipathd, error messages like below are logged onto /var/log/messages with non-multipathed devices:

Dec 30 19:56:21 geeklab multipathd: zram0: failed to get path uid
Dec 30 19:56:23 geeklab multipathd: xvdd: failed to get path uid
Dec 30 19:56:24 geeklab multipathd: xvda: failed to get path uid
Dec 30 19:56:36 geeklab multipathd: xvdb: failed to get path uid
Dec 30 19:56:36 geeklab multipathd: xvdc: failed to get path uid

The Solution

The devices are not configured to be ignored by multipathd (as they are not multipathed, are not necessary by multipathd), and they do not return device UID which multipathd needs to identify them.

The error messages can be safely ignored if the devices are not multipathed. In case they need to be suppressed, add appropriate blacklist description onto /etc/multipath.conf. For example:

blacklist {
    devnode "^(ram|raw|loop|fd|md|dm-|sr|scd|st|nbd)[0-9]*"
    devnode "^hd[a-z][0-9]*"
    devnode "^etherd"
    devnode "^nvme.*"
    devnode "^xvd[a-z]*"  # here
    devnode "^zram[0-9]*" # here
}