Re: "trapdoor uid"?

Karl Anders Oygard (
26 Nov 1996 16:13:00 +0100

[Ulf Jaenicke-Roessler]

| Warning: You appear to have a trapdoor gid system
| From 'man smbd' I learned, that the program was unable to change its
| uid to root and back. Is this a (local) misconfiguration (and what
| should I do to correct it)

It's probably because you have set the uid of `nobody' to -1. This is
wrong, because, for security reasons, samba uses setreuid() to change uid
from root to nobody. However, passing -1 to setreuid() won't work:


Supplying a value of -1 for either the real or effective user ID
forces the system to leave that ID unchanged.

The fix is to change nobody to e.g. -2.

Karl Anders Øygard <>, +47 6384 8862
Telenor Research and Development