Reserved UID and GID ranges on Linux

Debian Policy Manual § 9.2.2 UID and GID classes

Version 4.7.4.1, read 2026-08-07. Source

Range	Allocation	Class
0–99	static	Globally allocated by the Debian project, identical on every Debian system. Maintained in base-passwd.
100–999	dynamic	Dynamically allocated system users and groups. Created with adduser --system, which picks a free id according to adduser.conf.
1000–59999	dynamic	Dynamically allocated user accounts.
60000–64999	static	Globally allocated by the Debian project, but created only when needed.
65000–65533	reserved	Reserved.
65534–65534	static	The user nobody. The corresponding gid is the group nogroup.
65535–65535	prohibited	Must not be used. It was the error return value when uid_t was 16 bits.
65536–99999	dynamic	Dynamically allocated user accounts. adduser does not allocate here by default.
100000–600100000	dynamic	Dynamically allocated subordinate user ids (subuid).
600100001–4294967293	dynamic	Dynamically allocated user accounts. adduser does not allocate here by default.
4294967294–4294967294	prohibited	(uid_t)(-2). Used as the anonymous, unauthenticated user by some NFS implementations.
4294967295–4294967295	prohibited	(uid_t)(-1). Error return value.

Alpine Linux: no published range policy was found. No published UID/GID range policy for Alpine was found in the inspected aports tree. Searching the whole cloned tree for FIRST_SYSTEM_UID and LAST_SYSTEM_UID returns no matches. In practice Alpine allocates statically in alpine-baselayout, including above 100: ntp=123 and guest=405 as uids, abuild=300, utmp=406 and ping=999 as gids. The absence of a policy is recorded as an absence, not filled in with an assumption.

Sources

Distribution	Source package	Package version	Commit	Read from source
Debian	`base-passwd`	3.6.8	`a080557e1d59`	2026-08-07
Alpine Linux	`alpine-baselayout`	3.7.2	`a9c597c5cee0`	2026-08-07