[jabl]

Others pointed out that nobody was (uint16_t) -2, or 65534.

But, it turns out this value is, in fact, special in current day Linux as well. It's the default value of the special 'overflow' uid, can be seen/set at /proc/sys/fs/overflowuid.

Apart from some legacy stuff using 16-bit uid's, today it's mostly used for two things

1) In NFS, if mapping a user fails, then it gets assigned the overflowuid.

2) In containers with user namespaces, unmapped users again get the overflowuid.

For more details, see https://lwn.net/Articles/695478/

[emmelaich]

Very interesting, thanks.