Editing User identifier (section)

=== Special values ===
* 0: The [[superuser]] normally has a UID of zero (0).<ref>{{cite web|url=http://pubs.opengroup.org/onlinepubs/009695399/functions/getpwuid.html |title=Getpwuid |website=Pubs.opengroup.org |access-date=2016-09-24}}</ref>
* −1: The value <code>(uid_t) -1</code> is reserved by POSIX to identify an omitted argument.<ref>{{cite web|url=http://pubs.opengroup.org/onlinepubs/009695399/functions/chown.html |title=Chown |website=Pubs.opengroup.org |access-date=2016-09-24}}</ref>
* 65535: This value is still avoided because it was the API error return value when uid_t was 16 bits.
* Nobody: Historically, the user "[[nobody (username)|nobody]]" was assigned UID <code>-2</code> by several operating systems, although other values such as 2<sup>15</sup>−1 = 32,767 are also in use, such as by [[OpenBSD]].<ref>{{cite web|url=http://gnats.netbsd.org/6594 |title=NetBSD Problem Report #6594: the default "nobody" credentials (32767:9999) do not match mountd's default (-2:-2) |website=GnaNFSv4ts.netbsd.org |access-date=2016-09-24}}</ref> For compatibility between 16-bit and 32-bit UIDs, many Linux distributions now set it to be 2<sup>16</sup>−2 = 65,534; the Linux kernel defaults to returning this value when a 32-bit UID does not fit into the return value of the 16-bit system calls.<ref>{{cite web|url=https://lwn.net/Articles/532593/ |title=Namespaces in operation, part 5: User namespaces |website=Lwn.net |access-date=2016-09-24}}</ref> [[Fedora Linux]] assigns the last UID of the range statically allocated for system use (0–99) to nobody: 99, and calls 65534 instead <code>nfsnobody</code>.