[Linux] Manual Section Number 의미

man 명령어를 통해 각 커맨드의 사용법을 알 수 있는데, 동일한 커맨드의 경우 각 section number를 입력하면 원하는 command manual을 볼 수 있다.

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 Daemons

Example

$ man 2 open
OPEN(2)                                                                Linux Programmer's Manual                                                               

NAME
       open, openat, creat - open and possibly create a file

SYNOPSIS
       #include <sys/types.h>
       #include <sys/stat.h>
       #include <fcntl.h>

       int open(const char *pathname, int flags);
       int open(const char *pathname, int flags, mode_t mode);

       int creat(const char *pathname, mode_t mode);

       int openat(int dirfd, const char *pathname, int flags);
       int openat(int dirfd, const char *pathname, int flags, mode_t mode);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       openat():
           Since glibc 2.10:
               _POSIX_C_SOURCE >= 200809L
           Before glibc 2.10:
               _ATFILE_SOURCE