What is the difference between "man chmod" and "man 2 chmod" ?

Victor43 · 06-16-2020, 01:32 PM

Does "man 2 chmod" provide details on issuing a chmod function call and the "man chmod" describes details on the command line version of issuing a chmod command ?

Thanks

pan64 · 06-16-2020, 01:40 PM

see man man
2 is a section.

scasey · 06-16-2020, 01:42 PM

Quote:

Originally Posted by Victor43

Does "man 2 chmod" provide details on issuing a chmod function call and the "man chmod" describes details on the command line version of issuing a chmod command ?

Thanks

Probably.
It should clarify under NAME or DESCRIPTION in the man pages, but I don't have man 2 chmod on my systems, so I can't confirm.

ehartman · 06-16-2020, 01:57 PM

Quote:

Originally Posted by Victor43

Does "man 2 chmod" provide details on issuing a chmod function call and the "man chmod" describes details on the command line version of issuing a chmod command ?

The "2" section describes system calls that can be used by (mostly C) programs.
From "man 2 intro"

Quote:

Section 2 of the manual describes the Linux system calls. A system call is an entry point into the Linux kernel.

This call is used by the chmod command (which is in section 1), so its man page is more completely invoked as "man 1 chmod".
There are quite a few more cases where a command (in section 1) uses the same named system call (2) or library function (which is section 3).
So sections 2 and 3 are for programmers or people who want to know what the underlying calls do.

PS: each section of the man info pages has an introduction, that can be viewed with "man N intro" (with N being a number from 1 to 8).

hazel · 06-16-2020, 02:18 PM

By default, man uses the first match it finds, so a user command in Section 1 will always trump a system call of the same name in Section 2. Which is mostly what you want. If you do want to look up the system call, you can always specify section 2.

It becomes more problematic with the administrative commands in Section 8, because here a system call with the same name in Section 2 will be displayed preferentially. I've been caught that way a few times and it's very annoying.

ehartman · 06-16-2020, 03:32 PM

Quote:

Originally Posted by hazel

It becomes more problematic with the administrative commands in Section 8,

That is one of the reasons why a "real System V Unix" uses section 1M (for management) for those commands, instead of 8

Code:

The manual is generally split into eight numbered sections, organized as follows (on Research Unix, BSD, macOS and Linux):
Section 	Description
1 	General commands
2 	System calls
3 	Library functions, covering in particular the C standard library
4 	Special files (usually devices, those found in /dev) and drivers
5 	File formats and conventions
6 	Games and screensavers
7 	Miscellanea
8 	System administration commands and daemons

Unix System V uses a similar numbering scheme, except in a different order:
Section 	Description
1 	General commands
1M 	System administration commands and daemons
2 	System calls
3 	C library functions
4 	File formats and conventions
5 	Miscellanea
6 	Games and screensavers
7 	Special files (usually devices, those found in /dev) and drivers

(cut from en.wikipedia.org/wiki/Man_page#Manual_sections)

JeremyBoden · 06-16-2020, 04:23 PM

Incidentally,

Code:

whatis chmod

outputs something not very similar to the headings of man chmod & man 2 chmod

Quote:

chmod (1) - change file mode bits
chmod (2) - change permissions of a file

ehartman · 06-17-2020, 02:51 AM

Quote:

Originally Posted by JeremyBoden

Incidentally,

Code:

whatis chmod

outputs something not very similar to the headings of man chmod & man 2 chmod

The lines from "whatis" DO come from their respective man pages:
the "NAME" section:

Code:

 $ man chmod
NAME
       chmod - change file mode bits
vs
 $ man 2 chmod
NAME
       chmod, fchmod, fchmodat - change permissions of a file

(the latter - of course - will be 3 different entries in the whatis database).

JJJCR · 06-17-2020, 03:59 AM

Quote:

Originally Posted by pan64

see man man
2 is a section.

Or the OP should tried man to man

@OP see this link: https://unix.stackexchange.com/quest...-man-page-mean

From link above:

Quote:

The number corresponds to what section of the manual that page is from; 1 is user commands, while 8 is sysadmin stuff. The man page for man itself (man man) explains it and lists the standard ones:

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

Distributions customize the manual section to their specifics,
which often include additional sections.