man

man shows system manual pages.

There are 8 different sections to man:

• 1 → programs (grep, ls)
• 2 → System calls (sendfile, ptrace)
• 3 → C functions (printf, fopen)
• 4 → devices (null, tty)
• 5 → file fomats (sudoers, proc, ext4, elf, fstab)
• 6 → games (sl)
• 7 → misc (concepts, ex: pipe, symlink)
• 8 → sysadmin (apt, chroot)

At /usr/share/man/man2 you can view every manpage for that section.