4 ms·

I've been meaning to ask this for a very long time: What does the (2) mean? I see (n) in lots of descriptions of calls, but I've never found out what it means.

eru 16y ago
It refers to sections of the man pages. They are organized like this: 1. General Commands 2. System Calls 3. Subroutines 4. Special Files 5. File Formats 6. Games 7. Macros and Conventions 8. Maintenence Commands
- ramidarigaz 16y ago
  Exactly what I wanted to know. Thanks.
- cycojesus 16y ago
  and it's used like this: man 2 write
gxti 16y ago
It's the "man" section. According to "man man", 2 is the section for system calls. Often you'll have manpages for the same name under different sections, for example sync(1) is a command while sync(2) a system call (which, unsurprisingly, the sync command uses).
jbarham 16y ago
The Unix manual is divided into sections (http://en.wikipedia.org/wiki/Man_page#Manual_sections http://en.wikipedia.org/wiki/Man_page#Manual_sections). Section 2 is for system calls. Specifying the section number allows you to disambiguate which section of the manual you want to look in if a man page exists in multiple sections (e.g., "man 1 write" vs. "man 2 write").
bretthoerner 16y ago
It's the man page section number. I believe this dates back to when the man(uals) were actually printed out. You'd go to section 2 to find X to disambiguate from a different Y. http://www.december.com/unix/ref/mansec.html http://www.december.com/unix/ref/mansec.html
- eru 16y ago
  And the disambiguation is still useful.
stonemetal 16y ago
It is where it lives in man. man write returns write(1) an application that sends a message to another user. man 2 write returns write(2) the system call mentioned above(or at least it does on Ubuntu).
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tptacek 16y ago
You got a lot of good answers here, but just so you know: you really only have to remember that open(2) is a syscall and fopen(3) is a library call. That's the important distinction.

eru 16y ago

It refers to sections of the man pages. They are organized like this: 1. General Commands 2. System Calls 3. Subroutines 4. Special Files 5. File Formats 6. Games 7. Macros and Conventions 8. Maintenence Commands

ramidarigaz 16y ago
Exactly what I wanted to know. Thanks.
cycojesus 16y ago
and it's used like this: man 2 write

gxti 16y ago

It's the "man" section. According to "man man", 2 is the section for system calls. Often you'll have manpages for the same name under different sections, for example sync(1) is a command while sync(2) a system call (which, unsurprisingly, the sync command uses).

jbarham 16y ago

The Unix manual is divided into sections (http://en.wikipedia.org/wiki/Man_page#Manual_sections http://en.wikipedia.org/wiki/Man_page#Manual_sections). Section 2 is for system calls. Specifying the section number allows you to disambiguate which section of the manual you want to look in if a man page exists in multiple sections (e.g., "man 1 write" vs. "man 2 write").

bretthoerner 16y ago

It's the man page section number. I believe this dates back to when the man(uals) were actually printed out. You'd go to section 2 to find X to disambiguate from a different Y. http://www.december.com/unix/ref/mansec.html http://www.december.com/unix/ref/mansec.html

eru 16y ago
And the disambiguation is still useful.

stonemetal 16y ago

It is where it lives in man. man write returns write(1) an application that sends a message to another user. man 2 write returns write(2) the system call mentioned above(or at least it does on Ubuntu).

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tptacek 16y ago

You got a lot of good answers here, but just so you know: you really only have to remember that open(2) is a syscall and fopen(3) is a library call. That's the important distinction.