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UIDS-GIDS.md: explicitly mention one more user of the overflowuid

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File systems with only 16bit UID support (i.e. old ext2) also use the
overflowuid to map users they can't map. Briefly mention this.
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Lennart Poettering 2018-01-23 21:16:59 +01:00
parent 45a080944d
commit 2e276b1d9b
1 changed files with 8 additions and 7 deletions
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UIDS-GIDS.md
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@ -17,13 +17,14 @@ i.e. 0…4294967295. However, four UIDs are special on Linux:
1. 0 → The `root` super-user
2. 65534 → The `nobody` UID, also called the "overflow" UID or similar. It's
where various subsystems map unmappable users to, for example NFS or user
namespacing. (The latter can be changed with a sysctl during runtime, but
that's not supported on `systemd`. If you do change it you void your
warranty.) Because Fedora is a bit confused the `nobody` user is called
`nfsnobody` there (and they have a different `nobody` user at UID 99). I
hope this will be corrected eventually though. (Also, some distributions
call the `nobody` group `nogroup`. I wish they didn't.)
where various subsystems map unmappable users to, for example file systems
only supporting 16bit UIDs, NFS or user namespacing. (The latter can be
changed with a sysctl during runtime, but that's not supported on
`systemd`. If you do change it you void your warranty.) Because Fedora is a
bit confused the `nobody` user is called `nfsnobody` there (and they have a
different `nobody` user at UID 99). I hope this will be corrected eventually
though. (Also, some distributions call the `nobody` group `nogroup`. I wish
they didn't.)
3. 4294967295, aka "32bit `(uid_t) -1`" → This UID is not a valid user ID, as
`setresuid()`, `chown()` and friends treat -1 as a special request to not