What are the numbers in some unix manuals refering to?

Question

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What are the numbers in parentheses in the names of unix tools?

Hello, what these numbers I see in manual pages for linux commands?

See this gittutorial(7)[tutorial] to get started,
then see Everyday Git[1] for a useful   minimum set of commands,
and "man git-commandname" for documentation of each command.
CVS users may also want to read gitcvs-migration(7)[CVS migration].
See Git User's Manual[2] for a more in-depth introduction.

Answer 1

The numbers in parentheses ( and ) refer to different sections of "the manual". If you do man man, it will tell you which numbers correspond to which section of "the manual". Each operating system may use its own layout for man page sections. Here is the section layout of my Ubuntu system.

   1   Executable programs or shell commands
   2   System calls (functions provided by the kernel)
   3   Library calls (functions within program libraries)
   4   Special files (usually found in /dev)
   5   File formats and conventions eg /etc/passwd
   6   Games
   7   Miscellaneous (including macro  packages  and  conven‐
       tions), e.g. man(7), groff(7)
   8   System administration commands (usually only for root)
   9   Kernel routines [Non standard]

If you do man 1 printf, you get information about the shell utility printf, but if you do man 3 printf, you get information about the printf function in the C runtime.

The numbers in brackets [ and ] refer to external resources and should have locations or URLs described further in the article you're reading.