Talk:User identifier

Shadow does not store numeric IDs
''The UID value references users in the /etc/passwd file. Shadow password files and Network Information Service also refer to numeric UIDs.''

This is not accurate enough, because /etc/shadow does not store numeric UIDs, only the username (and password information).

I'm not sure if "Shadow password files" does mean passwd AND shadow, or only shadow. --CrazyTerabyte 19:22, 3 July 2006 (UTC)

tools?
It would sure be nice here to have a simple example command of how to retrieve UID/usernames in various linux/unix shells.. —Preceding unsigned comment added by 217.56.230.234 (talk) 08:47, 3 September 2007 (UTC)

Nobody
I dispute that 32767 is "the most-commonly value used for 'nobody'".

The "nobody" user was added when NFS was introduced, as a surrogate for the root user.

Back then, the corresponding numeric UID was 65534 or 4294967294, depending on whether the underlying uid_t type was 16 or 32 bit. These values both correspond to -2 (negative two) after conversion to an "unsigned int" type.

The value -2 was chosen because the usual manner of indicating errors was to return -1, while the usual manner of checking for errors was simply to check for any negative; hence a naive check would say "no such user", while a more sophisticated check would say "nobody".

Sometimes, particularly with System-V derived systems, the numeric value for "nobody" was often forced to meet normal UID allocation policy; hence other outlier values such as 32767 were chosen.

Linux distributions generally followed the earlier BSD policy, but mistakenly continued to use 65534 on kernels with 32-bit UID support.

Martin Kealey (talk) 03:40, 10 September 2013 (UTC)

Expand Special values section with low-uid users?
Maybe I'm alone in this, but I feel we need historical and current info covering the low-uid users and groups (bin, daemon, adm, lp, sys, et al.) under User_identifier. Each one could be an entire research project in itself, so I'm wary of contributing original research. Thoughts? --Rfsmit (talk) 18:37, 23 January 2020 (UTC)