Skip site navigation (1)Skip section navigation (2)

FreeBSD Man Pages

Man Page or Keyword Search:
Man Architecture
Apropos Keyword Search (all sections) Output format
home | help
INTRO(2)		   Linux Programmer's Manual		      INTRO(2)

NAME
       intro - Introduction to system calls

DESCRIPTION
       Section	2  of  the  manual describes the Linux system calls.  A	system
       call is an entry	point into the Linux kernel.   Usually,	 system	 calls
       are not invoked directly: instead, most system calls have corresponding
       C library wrapper functions which perform  the  steps  required	(e.g.,
       trapping	 to  kernel  mode)  in order to	invoke the system call.	 Thus,
       making a	system call looks the same as invoking a normal	library	 func-
       tion.

       For a list of the Linux system calls, see syscalls(2).

RETURN VALUE
       On  error,  most	system calls return a negative error number (i.e., the
       negated value of	one of the constants described in  errno(3)).	The  C
       library	wrapper	 hides this detail from	the caller: when a system call
       returns a negative value, the wrapper copies the	 absolute  value  into
       the  errno variable, and	returns	-1 as the return value of the wrapper.

       The value returned by a successful system call  depends	on  the	 call.
       Many system calls return	0 on success, but some can return nonzero val-
       ues from	a successful call.  The	details	are described in the  individ-
       ual manual pages.

       In some cases, the programmer must define a feature test	macro in order
       to obtain the declaration of a system call from the header file	speci-
       fied  in	 the  man  page	SYNOPSIS section.  In such cases, the required
       macro is	described in the man page.  For	further	information on feature
       test macros, see	feature_test_macros(7).

CONFORMING TO
       Certain	terms and abbreviations	are used to indicate Unix variants and
       standards to which calls	in this	section	conform.  See standards(7).

NOTES
   Calling Directly
       In most cases, it is unnecessary	to invoke a system call	directly,  but
       there  are  times when the Standard C library does not implement	a nice
       wrapper function	for you.  In this case,	the programmer	must  manually
       invoke  the  system call	using syscall(2).  Historically, this was also
       possible	using one of the _syscall macros described in _syscall(2).

   Authors and Copyright Conditions
       Look at the header of the manual	page  source  for  the	author(s)  and
       copyright  conditions.	Note  that these can be	different from page to
       page!

SEE ALSO
       _syscall(2), syscall(2),	errno(3), feature_test_macros(7), standards(7)

COLOPHON
       This  page  is  part of release 3.25 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found	at http://www.kernel.org/doc/man-pages/.

Linux				  2010-02-03			      INTRO(2)

NAME | DESCRIPTION | RETURN VALUE | CONFORMING TO | NOTES | SEE ALSO | COLOPHON

Want to link to this manual page? Use this URL:
<https://www.freebsd.org/cgi/man.cgi?query=intro&sektion=2&manpath=SuSE+Linux%2fi386+11.3>

home | help