I'm trying to add a user in the form "user.name" on a RHEL3 system, but useradd keeps telling me "invalid user name." Is there any way around it? That's probably some validation that useradd is doing.

Title pretty much says it. Searching for 'memtest86+' brings up results for 'memtest86'. But it also seems to find 'memtest86+' too, so it looks like it just ignores non alphanumeric characters. This ...