Merge pull request #15926 from fbuihuu/rework-show-status

[thirdparty/systemd.git] / docs / UIDS-GIDS.md

diff --git a/docs/UIDS-GIDS.md b/docs/UIDS-GIDS.md
index 77554913198a76e9282b57364f133ec301e3668d..c41c4d7eec7a75a5bed03509e7c6a6eb96a184ff 100644 (file)
--- a/docs/UIDS-GIDS.md
+++ b/docs/UIDS-GIDS.md
@@ -1,4 +1,10 @@
-# Users, Groups, UIDs and GIDs on `systemd` systems
+---
+title: Users, Groups, UIDs and GIDs on systemd Systems
+category: Users, Groups and Home Directories
+layout: default
+---
+
+# Users, Groups, UIDs and GIDs on systemd Systems
 
 Here's a summary of the requirements `systemd` (and Linux) make on UID/GID
 assignments and their ranges.
@@ -90,7 +96,15 @@ but downstreams are strongly advised against doing that.)
 
 `systemd` defines a number of special UID ranges:
 
-1. 61184…65519 → UIDs for dynamic users are allocated from this range (see the
+1. 60001…60513 → UIDs for home directories managed by
+   [`systemd-homed.service(8)`](https://www.freedesktop.org/software/systemd/man/systemd-homed.service.html). UIDs
+   from this range are automatically assigned to any home directory discovered,
+   and persisted locally on first login. On different systems the same user
+   might get different UIDs assigned in case of conflict, though it is
+   attempted to make UID assignments stable, by deriving them from a hash of
+   the user name.
+
+2. 61184…65519 → UIDs for dynamic users are allocated from this range (see the
    `DynamicUser=` documentation in
    [`systemd.exec(5)`](https://www.freedesktop.org/software/systemd/man/systemd.exec.html)). This
    range has been chosen so that it is below the 16bit boundary (i.e. below
@@ -105,7 +119,7 @@ but downstreams are strongly advised against doing that.)
    user record resolving works correctly without those users being in
    `/etc/passwd`.
 
-2. 524288…1879048191 → UID range for `systemd-nspawn`'s automatic allocation of
+3. 524288…1879048191 → UID range for `systemd-nspawn`'s automatic allocation of
    per-container UID ranges. When the `--private-users=pick` switch is used (or
    `-U`) then it will automatically find a so far unused 16bit subrange of this
    range and assign it to the container. The range is picked so that the upper
@@ -226,14 +240,16 @@ the artifacts the container manager persistently leaves in the system.
 |                     5 | `tty` group           | `systemd`     | `/etc/passwd`                 |
 |                 6…999 | System users          | Distributions | `/etc/passwd`                 |
 |            1000…60000 | Regular users         | Distributions | `/etc/passwd` + LDAP/NIS/…    |
-|           60001…61183 | Unused                |               |                               |
+|           60001…60513 | Human Users (homed)   | `systemd`     | `nss-systemd`
+|           60514…61183 | Unused                |               |                               |
 |           61184…65519 | Dynamic service users | `systemd`     | `nss-systemd`                 |
 |           65520…65533 | Unused                |               |                               |
 |                 65534 | `nobody` user         | Linux         | `/etc/passwd` + `nss-systemd` |
 |                 65535 | 16bit `(uid_t) -1`    | Linux         |                               |
 |          65536…524287 | Unused                |               |                               |
 |     524288…1879048191 | Container UID ranges  | `systemd`     | `nss-mymachines`              |
-| 1879048192…4294967294 | Unused                |               |                               |
+| 1879048192…2147483647 | Unused                |               |                               |
+| 2147483648…4294967294 | HIC SVNT LEONES       |               |                               |
 |            4294967295 | 32bit `(uid_t) -1`    | Linux         |                               |
 
 Note that "Unused" in the table above doesn't meant that these ranges are
@@ -242,6 +258,13 @@ pre-defined purposes between Linux, generic low-level distributions and
 `systemd`. There might very well be other packages that allocate from these
 ranges.
 
+Note that the range 2147483648…4294967294 (i.e. 2^31…2^32-2) should be handled
+with care. Various programs (including kernel file systems, see `devpts`) have
+trouble with UIDs outside of the signed 32bit range, i.e any UIDs equal to or
+above 2147483648. It is thus strongly recommended to stay away from this range
+in order to avoid complications. This range should be considered reserved for
+future, special purposes.
+
 ## Notes on resolvability of user and group names
 
 User names, UIDs, group names and GIDs don't have to be resolvable using NSS