Mastodawn

Number in man page titles e.g. sleep(3)

https://lalitm.com/til-number-in-man-page-titles-e-g-sleep-3/

TIL: Number in man page titles (e.g. sleep(3))

If you do Linux systems programming, you will have likely pored over man pages, either on the command line or, my personal preference, using the excellent man7.org or linux.die.net. I’ve always seen the numbers in sleep(3) and read(2) and idly wondered what they meant, but never actually bothered to look them up. That is, until a review comment on a pull request: // Behaves like man 2 basename reviewer: nit: it’s not a syscall, so “man 2” is incorrect So I looked it up. The answer was in the man(1) page (also accessible via the delightful man man command): The table below shows the section numbers of the manual followed by the types of pages they contain. 1 Executable programs or shell commands 2 System calls (functions provided by the kernel) 3 Library calls (functions within program libraries) (... less common section numbers) So my colleague was right and the code should have read // behaves like man 3 basename as basename(3) is a libc library call.

Lalit Maganti

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gerikson 1d ago

> (... less common section numbers)

One very important section number is 5 - it's for file formats. So if you forget the crontab format, you need to invoke `man 5 crontab` to read about it.

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linsomniac 1d ago

... because if you do `man crontab` you get section 1, which does not document the crontab fields.

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driftcoder 1d ago

man -k crontab is the real trick here. shows both sections so you don't have to already know the number exists.

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voidUpdate 1d ago

It only shows a description though.

Incidentally, man --help on my machine shows "-k, --apropos equivalent to apropos", which isn't very useful. I know the two are equivalent, because they're on the same line of switches, what does it actually do?

With some further man digging, apropos is actually a separate program that looks through man page names/descriptions for the argument. Unless you run it with no arguments, in which case it just outputs "apropos what?" Instead of an actual error message like "No search term provided" or something

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simoncion

> Incidentally, man --help on my machine shows "-k, --apropos equivalent to apropos", which isn't very useful.

That's your hint to execute either 'man apropos' or 'man man'. Both tell you in detail what the flag and utility do.

You seem likely to be very disappointed in the '-h'/'-H' output of utilities from the BSD tradition. The output is often a list of all of the (almost always exclusively short) options presented as a sea of characters... and nothing else.