Unix FAQ/faq

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Subject: When someone refers to 'rn(1)' ... the number in parentheses mean?

Date: Tue, 13 Dec 1994 16:37:26 -0500

1.2) When someone refers to 'rn(1)' or 'ctime(3)', what does the number in parentheses mean?

It looks like some sort of function call, but it isn't. These numbers refer to the section of the "Unix manual" where the appropriate documentation can be found. You could type "man 3 ctime" to look up the manual page for "ctime" in section 3 of the manual.

The traditional manual sections are:

1. User-level commands
2. System calls
3. Library functions
4. Devices and device drivers
5. File formats
6. Games
7. Various miscellaneous stuff - macro packages etc.
8. System maintenance and operation commands

Some Unix versions use non-numeric section names. For instance, Xenix uses "C" for commands and "S" for functions. Some newer versions of Unix require "man -s# title" instead of "man # title". Each section has an introduction, which you can read with "man # intro" where # is the section number. Sometimes the number is necessary to differentiate between a command and a library routine or system call of the same name. For instance, your system may have "time(1)", a manual page about the 'time' command for timing programs, and also "time(3)", a manual page about the 'time' subroutine for determining the current time.

You can use "man 1 time" or "man 3 time" to specify which "time" man page you're interested in. You'll often find other sections for local programs or even subsections of the sections above - Ultrix has sections 3m, 3n, 3x and 3yp among others.

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