+++ /dev/null
-.\" Copyright (C) 2007 Michael Kerrisk <mtk.manpages@gmail.com>
-.\"
-.\" %%%LICENSE_START(VERBATIM)
-.\" Permission is granted to make and distribute verbatim copies of this
-.\" manual provided the copyright notice and this permission notice are
-.\" preserved on all copies.
-.\"
-.\" Permission is granted to copy and distribute modified versions of this
-.\" manual under the conditions for verbatim copying, provided that the
-.\" entire resulting derived work is distributed under the terms of a
-.\" permission notice identical to this one.
-.\"
-.\" Since the Linux kernel and libraries are constantly changing, this
-.\" manual page may be incorrect or out-of-date. The author(s) assume no
-.\" responsibility for errors or omissions, or for damages resulting from
-.\" the use of the information contained herein. The author(s) may not
-.\" have taken the same level of care in the production of this manual,
-.\" which is licensed free of charge, as they might when working
-.\" professionally.
-.\"
-.\" Formatted or processed versions of this manual, if unaccompanied by
-.\" the source, must acknowledge the copyright and authors of this work.
-.\" %%%LICENSE_END
-.\"
-.\" 2007-10-23 mtk: moved the _syscallN specific material to the
-.\" new _syscall(2) page, and substantially enhanced and rewrote
-.\" the remaining material on this page.
-.\"
-.TH INTRO 2 2014-02-20 "Linux" "Linux Programmer's Manual"
-.SH NAME
-intro \- introduction to system calls
-.SH 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 function.
-
-In many cases, the C library wrapper function does nothing more than:
-.IP * 3
-copying arguments and the unique system call number to the
-registers where the kernel expects them;
-.IP *
-trapping to kernel mode,
-at which point the kernel does the real work of the system call; and
-.IP *
-setting
-.I errno
-if the system call returns an error number when the kernel returns the
-CPU to user mode.
-.LP
-However, in a few cases, a wrapper function may do rather more than this,
-for example, performing some preprocessing
-of the arguments of arguments before trapping to kernel mode,
-or postprocessing of values returned by the system call.
-Where this is the case, the manual pages in Section 2 generally
-try to note the details of both the (usually GNU) C library API
-interface and the raw system call.
-Most commonly, the main DESCRIPTION will focus on the C library interface,
-and differences for the system call are covered in the NOTES section.
-
-For a list of the Linux system calls, see
-.BR syscalls (2).
-.SH RETURN VALUE
-On error, most system calls return a negative error number
-(i.e., the negated value of one of the constants described in
-.BR 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
-.I 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
-values from a successful call.
-The details are described in the individual 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 specified
-in the man page SYNOPSIS section.
-(Where required, these feature test macros must be defined before including
-.I any
-header files.)
-In such cases, the required macro is described in the man page.
-For further information on feature test macros, see
-.BR feature_test_macros (7).
-.SH CONFORMING TO
-Certain terms and abbreviations are used to indicate UNIX variants
-and standards to which calls in this section conform.
-See
-.BR standards (7).
-.SH NOTES
-.SS 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
-.BR syscall (2).
-Historically, this was also possible using one of the _syscall macros
-described in
-.BR _syscall (2).
-.SS 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!
-.SH SEE ALSO
-.ad l
-.nh
-.BR _syscall (2),
-.BR syscall (2),
-.BR syscalls (2),
-.BR errno (3),
-.BR intro (3),
-.BR capabilities (7),
-.BR credentials (7),
-.BR feature_test_macros (7),
-.BR mq_overview (7),
-.BR path_resolution (7),
-.BR pipe (7),
-.BR pty (7),
-.BR sem_overview (7),
-.BR shm_overview (7),
-.BR signal (7),
-.BR socket (7),
-.BR standards (7),
-.BR svipc (7),
-.BR symlink (7),
-.BR time (7)
-.SH COLOPHON
-This page is part of release 3.79 of the Linux
-.I man-pages
-project.
-A description of the project,
-information about reporting bugs,
-and the latest version of this page,
-can be found at
-\%http://www.kernel.org/doc/man\-pages/.
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