Why do programs in Unix-like environments have numbers after their name? [duplicate]

Question

This question already has an answer here:

• What does the number in parentheses shown after Unix command names in manpages mean? 6 answers

For example, when I run man ioctl the page says IOCTL(2) at the top. What does that mean? Is there an IOCTL(1)? And how does one navigate between these?

Answer 1

It's the man page section. From memory, section 1 is user programs, 2 is system calls, and 3 is standard C library calls, and 5 is file formats.

Wikipedia has the full explanation here.

Answer 2

That's the man page section number. For example

 man printf

(should) Give you section 1, printf the bash command, while

 man 3 printf

gives you the C function printf.