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What the sections of the Unix manual are

From man man:

MANUAL SECTIONS
       The standard sections of the manual include:

       1      User Commands

       2      System Calls

       3      C Library Functions

       4      Devices and Special Files

       5      File Formats and Conventions

       6      Games et. Al.

       7      Miscellanea

       8      System Administration tools and Deamons

You can see the sections that have pages for a given query with man -f or whatis. E.g.

$ man -f passwd
passwd(1)                   - modify a user's password
passwd(5), master.passwd(5) - format of the password file
slapd-passwd(5)             - /etc/passwd backend to slapd

The section number is in parentheses. These can be used to open a man page from a particular section. Use:

$ man 1 passwd

to learn about how to use the passwd command and:

$ man 5 passwd

to learn about the format of the password file.