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I understood that man <command> is the manual page for any command.

For man groupdel is possible see only two options:

-h --help -R --root CHRROT_DIR

Until here at a first glance one can assume this command only supports 2 options, but

through groupdel -h shows:

-h --help -R --root CHRROT_DIR -f --force

So - Why -f was not shown through the man?. Not sure if this behavior happens for other commands - is this behavior either normal or expected in Linux?. BTW It is for Ubuntu Server 18:04

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This is an oversight, which has since been addressed.

Man pages are generally expected to be complete, with the exception of those provided by the GNU project; the latter favours info documents, and tends to provide abbreviated man pages. However it often happens that documentation in general is addressed separately from code, so man pages can end up being out-of-date whereas built-in help is usually complete. If you come across other incomplete documentation, feel free to file a bug!

In some cases features are deliberately omitted from documentation and/or built-in help, e.g. when options are deprecated and only provided for backward compatibility, or are intended only for debugging purposes, or are dangerous (in which case they should be documented in the man page but might not show up in the built-in help).

Some projects ship man pages generated from the built-in help using a tool such as help2man, in which case both end up being identical.

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    Note that it sometimes happens that options are deliberately omitted from man pages and usage information, like when their use is discouraged and they are only provided for backward compatibility or compatibility to other systems or may be removed in later versions without notice (see for instance GNU sed which used to favour -r over -E, didn't document the latter but still provided it for compatibility with BSD sed, or the ---disable-inotify option of GNU tail) Commented Oct 1, 2021 at 5:56
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    Good point, also when options are dangerous. Commented Oct 1, 2021 at 6:00
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    Surely if they're dangerous it would make more sense to document them thoroughly? Commented Oct 1, 2021 at 6:56
  • @roaima how many questions on this very site are the result of dangerous options not being understood, regardless of how well (or not) documented they are? I do agree that dangerous options should be documented, but they don’t have to be documented everywhere — I can’t remember right now where, but I have seen dangerous options which are mentioned in notes in the man page but aren’t listed in usage messages (hence the “and/or” in my last paragraph, which admittedly isn’t as clear as it should be). Commented Oct 1, 2021 at 7:11
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    @Manuel I’m using Debian, but the packages are the same in Ubuntu (at least for groupdel). dpkg -S groupdel told me that groupdel is shipped in the passwd package; I went to the Debian tracker page for that and followed the “Homepage” link which took me to the shadow project on GH. Commented Oct 1, 2021 at 13:14

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