予約済み uid gid ユーザID グループID

予約済みUID/GID

user id group id

CentOS

/usr/share/doc/setup-2.8.14/uidgid

http://ja.528p.com/linux/centos6/B005-uidgid.html

debian

/usr/share/doc/debian-policy/policy.txt.gz

100-999 がシステム用らしい。

UID や GID の範囲 - エンジニアきまぐれTips

UIDs 0-99 are globally allocated by the Debian project and are used for system accounts. The "root" account, for instance, is UID 0.
UIDs 100-999 are for system users which have not been allocated by the Debian project.
UIDs 1000-29999 are normal user accounts.
UID 65534 is user "nobody", an account with no rights or permissions.

Usernames User IDs Groups and Group IDs in Debian Linux

FreeBSD

https://github.com/freebsd/freebsd-ports/blob/main/UIDs

http://www.si.freebsd.org/doc/ja/books/porters-handbook/dads-uid.html