.\" Copyright (C) 2007 Michael Kerrisk <mtk.manpages@gmail.com>
.\" with some input from Stepan Kasal <kasal@ucw.cz>
.\"
.\" Some content retained from an earlier version of this page:
.\" Copyright (C) 1998 Andries Brouwer (aeb@cwi.nl)
.\" Modifications for 2.2 and 2.4 Copyright (C) 2002 Ian Redfern
.\" <redferni@logica.com>
.\"
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.\" 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.\" manual page may be incorrect or out-of-date.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.
.\"
.TH SYSCALLS 2 2010-03-06 "Linux" "Linux Programmer's Manual"
.SH NAME
syscalls \- Linux system calls
.SH SYNOPSIS
Linux system calls.
.SH DESCRIPTION
The system call is the fundamental interface between an application
and the Linux kernel.
.SS System calls and library wrapper functions
System calls are generally not invoked directly,
but rather via wrapper functions in glibc (or perhaps some other library).
For details of direct invocation of a system call, see
.BR intro (2).
Often, but not always, the name of the wrapper function is the same
as the name of the system call that it invokes.
For example, glibc contains a function
.BR truncate ()
which invokes the underlying "truncate" system call.

Often the glibc wrapper function is quite thin, doing little work
other than copying arguments to the right registers
before invoking the system call,
and then setting
.I errno
appropriately after the system call has returned.
(These are the same steps that are performed by
.BR syscall (2),
which can be used to invoke system calls
for which no wrapper function is provided.)
Note: system calls indicate a failure by returning a negative error
number to the caller;
when this happens,
the wrapper function negates the returned error number
(to make it positive), copies it to
.IR errno ,
and returns \-1 to the caller of the wrapper.

Sometimes, however, the wrapper function does some extra work
before invoking the system call.
For example, nowadays there are (for reasons described below) two
related system calls,
.BR truncate (2)
and
.BR truncate64 (2),
and the glibc
.BR truncate ()
wrapper function checks which of those system calls
are provided by the kernel and determines which should be employed.
.SS System call list
Below is a list of those system calls that are common to most platforms.
In the list, the
.I Kernel
column indicates the kernel version
for those system calls that were new in Linux 2.2,
or have appeared since that kernel version.
Note the following points:
.IP * 3
Where no kernel version is indicated,
the system call appeared in kernel 1.0 or earlier.
.IP *
Where a system call is marked "1.2"
this means the system call probably appeared in a 1.1.x kernel version,
and first appeared in a stable kernel with 1.2.
(Development of the 1.2 kernel was initiated from a branch of kernel
1.0.6 via the 1.1.x unstable kernel series.)
.IP *
Where a system call is marked "2.0"
this means the system call probably appeared in a 1.3.x kernel version,
and first appeared in a stable kernel with 2.0.
(Development of the 2.0 kernel was initiated from a branch of kernel
1.2.x, somewhere around 1.2.10,
via the 1.3.x unstable kernel series.)
.\" Was kernel 2.0 started from a branch of 1.2.10?
.\" At least from the timestamps of the tarballs of
.\" of 1.2.10 and 1.3.0, that's how it looks, but in
.\" fact the diff doesn't seem very clear, the
.\" 1.3.0 .tar.bz is much bigger (2.0 MB) than the
.\" 1.2.10 .tar.bz2 (1.8 MB), and AEB points out the
.\" timestamps of some files in 1.3.0 seem to be older
.\" than those in 1.2.10.  All of this suggests
.\" that there might not have been a clean branch point.
.IP *
Where a system call is marked "2.2"
this means the system call probably appeared in a 2.1.x kernel version,
and first appeared in a stable kernel with 2.2.0.
(Development of the 2.2 kernel was initiated from a branch of kernel
2.0.21 via the 2.1.x unstable kernel series.)
.IP *
Where a system call is marked "2.4"
this means the system call probably appeared in a 2.3.x kernel version,
and first appeared in a stable kernel with 2.4.0.
(Development of the 2.4 kernel was initiated from a branch of
kernel 2.2.8 via the 2.3.x unstable kernel series.)
.IP *
Where a system call is marked "2.6"
this means the system call probably appeared in a 2.5.x kernel version,
and first appeared in a stable kernel with 2.6.0.
(Development of kernel 2.6 was initiated from a branch
of kernel 2.4.15 via the 2.5.x unstable kernel series.)
.IP *
Starting with kernel 2.6.0, the development model changed,
and new system calls may appear in each 2.6.x release.
In this case, the exact version number where the system call appeared
is shown.
.IP *
In some cases, a system call was added to a stable kernel
series after it branched from the previous stable kernel
series, and then backported into the earlier stable kernel series.
For example some system calls that appeared in 2.6.x were also backported
into a 2.4.x release after 2.4.15.
When this is so, the version where the system call appeared
in both of the major kernel series is listed.
.PP
The list of system calls that are available as at kernel 2.6.33
(or in a few cases only on older kernels) is as follows:
.\"
.\" Looking at scripts/checksyscalls.sh in the kernel source is
.\" instructive about i386 specifics.
.\"
.TS
l l l
---
l l l.
\fBSystem call\fP	\fBKernel\fP	\fBNotes\fP

\fB_llseek\fP(2)	1.2
\fB_newselect\fP(2)
\fB_sysctl\fP(2)
\fBaccept\fP(2)
\fBaccept4\fP(2)	2.6.28
\fBaccess\fP(2)
\fBacct\fP(2)
\fBadd_key\fP(2)	2.6.11
\fBadjtimex\fP(2)
\fBafs_syscall\fP(2)		Not implemented
\fBalarm\fP(2)
\fBalloc_hugepages\fP(2)	2.5.36	Removed in 2.5.44
\fBbdflush\fP(2)
\fBbind\fP(2)
\fBbreak\fP(2)		Not implemented
\fBbrk\fP(2)
\fBcacheflush\fP(2)	1.2	Not on i386
\fBcapget\fP(2)	2.2
\fBcapset\fP(2)	2.2
\fBchdir\fP(2)
\fBchmod\fP(2)
\fBchown\fP(2)
\fBchown32\fP(2)	2.4
\fBchroot\fP(2)
\fBclock_getres\fP(2)	2.6
\fBclock_gettime\fP(2)	2.6
\fBclock_nanosleep\fP(2)	2.6
\fBclock_settime\fP(2)	2.6
\fBclone\fP(2)
\fBclose\fP(2)
\fBconnect\fP(2)
\fBcreat\fP(2)
\fBcreate_module\fP(2)
\fBdelete_module\fP(2)
\fBdup\fP(2)
\fBdup2\fP(2)
\fBdup3\fP(2)	2.6.27
\fBepoll_create\fP(2)	2.6
\fBepoll_create1\fP(2)	2.6.27
\fBepoll_ctl\fP(2)	2.6
\fBepoll_pwait\fP(2)	2.6.19
\fBepoll_wait\fP(2)	2.6
\fBeventfd\fP(2)	2.6.22
\fBeventfd2\fP(2)	2.6.27
\fBexecve\fP(2)
\fBexit\fP(2)
\fBexit_group\fP(2)	2.6
\fBfaccessat\fP(2)	2.6.16
\fBfadvise64\fP(2)	2.6
.\" Implements \fBposix_fadvise\fP(2)
\fBfadvise64_64\fP(2)	2.6
\fBfallocate\fP(2)	2.6.23
\fBfchdir\fP(2)
\fBfchmod\fP(2)
\fBfchmodat\fP(2)	2.6.16
\fBfchown\fP(2)
\fBfchown32\fP(2)	2.4
\fBfchownat\fP(2)	2.6.16
\fBfcntl\fP(2)
\fBfcntl64\fP(2)	2.4
\fBfdatasync\fP(2)
\fBfgetxattr\fP(2)	2.6; 2.4.18
\fBflistxattr\fP(2)	2.6; 2.4.18
\fBflock\fP(2)	2.0
\fBfork\fP(2)
\fBfree_hugepages\fP(2)	2.5.36	Removed in 2.5.44
\fBfremovexattr\fP(2)	2.6; 2.4.18
\fBfsetxattr\fP(2)	2.6; 2.4.18
\fBfstat\fP(2)
\fBfstat64\fP(2)	2.4
\fBfstatat64\fP(2)	2.6.16
\fBfstatfs\fP(2)
\fBfstatfs64\fP(2)	2.6
\fBfsync\fP(2)
\fBftime\fP(2)		Not implemented
.\" Implemented in glibc; see \fBftime\fP(3)
\fBftruncate\fP(2)
\fBftruncate64\fP(2)	2.4
\fBfutex\fP(2)	2.6
\fBfutimesat\fP(2)	2.6.16
\fBget_kernel_syms\fP(2)
\fBget_mempolicy\fP(2)	2.6.6
\fBget_robust_list\fP(2)	2.6.17
\fBget_thread_area\fP(2)	2.6
\fBgetcpu\fP(2)	2.6.19
\fBgetcwd\fP(2)	2.2
\fBgetdents\fP(2)	2.0
\fBgetdents64\fP(2)	2.4
\fBgetegid\fP(2)
\fBgetegid32\fP(2)	2.4
\fBgeteuid\fP(2)
\fBgeteuid32\fP(2)	2.4
\fBgetgid\fP(2)
\fBgetgid32\fP(2)	2.4
\fBgetgroups\fP(2)
\fBgetgroups32\fP(2)	2.4
\fBgetitimer\fP(2)
\fBgetpeername\fP(2)
\fBgetpagesize\fP(2)	2.0	Not on i386
\fBgetpgid\fP(2)
\fBgetpgrp\fP(2)
\fBgetpid\fP(2)
\fBgetpmsg\fP(2)		Not implemented
.\" Reserved for STREAMS support
\fBgetppid\fP(2)
\fBgetpriority\fP(2)
\fBgetresgid\fP(2)	2.2
\fBgetresgid32\fP(2)	2.4
\fBgetresuid\fP(2)	2.2
\fBgetresuid32\fP(2)	2.4
\fBgetrlimit\fP(2)
\fBgetrusage\fP(2)
\fBgetsid\fP(2)	2.0
\fBgetsockname\fP(2)
\fBgetsockopt\fP(2)
\fBgettid\fP(2)	2.4.11
\fBgettimeofday\fP(2)
\fBgetuid\fP(2)
\fBgetuid32\fP(2)	2.4
.\" \fBgetunwind\fP(2)	2.4.8	ia64; DEPRECATED
\fBgetxattr\fP(2)	2.6; 2.4.18
\fBgtty\fP(2)		Not implemented
\fBidle\fP(2)		Not implemented
\fBinit_module\fP(2)
\fBinotify_add_watch\fP(2)	2.6.13
\fBinotify_init\fP(2)	2.6.13
\fBinotify_init1\fP(2)	2.6.27
\fBinotify_rm_watch\fP(2)	2.6.13
\fBio_cancel\fP(2)	2.6
\fBio_destroy\fP(2)	2.6
\fBio_getevents\fP(2)	2.6
\fBio_setup\fP(2)	2.6
\fBio_submit\fP(2)	2.6
\fBioctl\fP(2)
\fBioperm\fP(2)
\fBiopl\fP(2)
\fBioprio_get\fP(2)	2.6.13
\fBioprio_set\fP(2)	2.6.13
\fBipc\fP(2)
.\" Implements System V IPC calls
\fBkexec_load\fP(2)	2.6.7
.\" Was named sys_kexec_load() from 2.6.7 to 2.6.16
\fBkeyctl\fP(2)	2.6.11
\fBkill\fP(2)
\fBlchown\fP(2)	2.2
\fBlchown32\fP(2)	2.4
\fBlgetxattr\fP(2)	2.6; 2.4.18
\fBlink\fP(2)
\fBlinkat\fP(2)	2.6.16
\fBlisten\fP(2)
\fBlistxattr\fP(2)	2.6; 2.4.18
\fBllistxattr\fP(2)	2.6; 2.4.18
\fBlock\fP(2)		Not implemented
\fBlookup_dcookie\fP(2)	2.6
\fBlremovexattr\fP(2)	2.6; 2.4.18
\fBlseek\fP(2)
\fBlsetxattr\fP(2)	2.6; 2.4.18
\fBlstat\fP(2)
\fBlstat64\fP(2)	2.4
\fBmadvise\fP(2)	2.4
\fBmadvise1\fP(2)	2.4
\fBmbind\fP(2)	2.6.6
.\" \fBmemory_ordering\fP(2)	???	Sparc64
\fBmigrate_pages\fP(2)	2.6.16
\fBmincore\fP(2)	2.4
\fBmkdir\fP(2)
\fBmkdirat\fP(2)	2.6.16
\fBmknod\fP(2)
\fBmknodat\fP(2)	2.6.16
\fBmlock\fP(2)
\fBmlockall\fP(2)
\fBmmap\fP(2)
\fBmmap2\fP(2)	2.4
\fBmodify_ldt\fP(2)
\fBmount\fP(2)
\fBmove_pages\fP(2)	2.6.18
\fBmprotect\fP(2)
\fBmpx\fP(2)		Not implemented
\fBmq_getsetattr\fP(2)	2.6.6
.\" Implements \fBmq_getattr\fP(3) and \fBmq_setattr\fP(3)
\fBmq_notify\fP(2)	2.6.6
\fBmq_open\fP(2)	2.6.6
\fBmq_timedreceive\fP(2)	2.6.6
\fBmq_timedsend\fP(2)	2.6.6
\fBmq_unlink\fP(2)
\fBmremap\fP(2)	2.0
\fBmsgctl\fP(2)
\fBmsgget\fP(2)
\fBmsgrcv\fP(2)
\fBmsgsnd\fP(2)
\fBmsync\fP(2)	2.0
.\" \fBmultiplexer\fP(2)	??	__NR_multiplexer reserved on
.\"		PowerPC, but unimplemented?
\fBmunlock\fP(2)
\fBmunlockall\fP(2)
\fBmunmap\fP(2)
\fBnanosleep\fP(2)	2.0
\fBnfsservctl\fP(2)	2.2
\fBnice\fP(2)
\fBoldfstat\fP(2)
\fBoldlstat\fP(2)
\fBoldolduname\fP(2)
\fBoldstat\fP(2)
\fBolduname\fP(2)
\fBopen\fP(2)
\fBopenat\fP(2)	2.6.16
\fBpause\fP(2)
\fBpciconfig_iobase\fP(2)	2.2.15; 2.4	Not on i386
.\" Alpha, PowerPC, ARM; not i386
\fBpciconfig_read\fP(2)	2.0.26; 2.2	Not on i386
.\" , PowerPC, ARM; not i386
\fBpciconfig_write\fP(2)	2.0.26; 2.2	Not on i386
.\" , PowerPC, ARM; not i386
\fBperf_event_open\fP(2)	2.6.31	Was called perf_counter_open()
		in 2.6.31; renamed in 2.6.32
\fBpersonality\fP(2)	1.2
.\" \fBperfctr\fP(2)	???	Sparc32, Sparc64
.\" \fBperfmonctl\fP(2)	???	ia64
\fBphys\fP(2)		Not implemented
.\" Unimplemented (no slot since 2.1.116)
\fBpipe\fP(2)
\fBpipe2\fP(2)	2.6.27
\fBpivot_root\fP(2)	2.4
\fBpoll\fP(2)	2.2
\fBppoll\fP(2)	2.6.16
\fBprctl\fP(2)	2.2
\fBpread64\fP(2)		Added as "pread" in 2.2;
		renamed "pread64" in 2.6
\fBpreadv\fP(2)	2.6.30
\fBprof\fP(2)		Not implemented
\fBprofil\fP(2)		Not implemented
.\" Implemented in glibc; see \fBprofil\fP(3)
\fBpselect6\fP(2)	2.6.16
.\" Implements \fBpselect\fP(2)
\fBptrace\fP(2)
\fBputpmsg\fP(2)		Not implemented
.\" Reserved for STREAMS support
\fBpwrite64\fP(2)		Added as "pwrite" in 2.2;
		renamed "pwrite64" in 2.6
\fBpwritev\fP(2)	2.6.30
\fBquery_module\fP(2)	2.2
\fBquotactl\fP(2)
\fBread\fP(2)
\fBreadahead\fP(2)	2.4.13
\fBreaddir\fP(2)
.\" Supersedes \fBgetdents\fP(2)
\fBreadlink\fP(2)
\fBreadlinkat\fP(2)	2.6.16
\fBreadv\fP(2)	2.0
\fBreboot\fP(2)
\fBrecv\fP(2)
\fBrecvfrom\fP(2)
\fBrecvmsg\fP(2)
\fBrecvmmsg\fP(2)	2.6.33
\fBremap_file_pages\fP(2)	2.6
\fBremovexattr\fP(2)	2.6; 2.4.18
\fBrename\fP(2)
\fBrenameat\fP(2)	2.6.16
\fBrequest_key\fP(2)	2.6.11
\fBrestart_syscall\fP(2)	2.6
\fBrmdir\fP(2)
\fBrt_sigaction\fP(2)	2.2
\fBrt_sigpending\fP(2)	2.2
\fBrt_sigprocmask\fP(2)	2.2
\fBrt_sigqueueinfo\fP(2)	2.2
.\" Implements \fBsigqueue\fP(2)
\fBrt_sigreturn\fP(2)	2.2
\fBrt_sigsuspend\fP(2)	2.2
\fBrt_sigtimedwait\fP(2)	2.2
\fBrt_tgsigqueueinfo\fP(2)	2.6.31
.\" Implements \fBpthread_sigqueue\fP(3)
\fBsched_get_priority_max\fP(2)	2.0
\fBsched_get_priority_min\fP(2)	2.0
\fBsched_getaffinity\fP(2)	2.6
\fBsched_getparam\fP(2)	2.0
\fBsched_getscheduler\fP(2)	2.0
\fBsched_rr_get_interval\fP(2)	2.0
\fBsched_setaffinity\fP(2)	2.6
\fBsched_setparam\fP(2)	2.0
\fBsched_setscheduler\fP(2)	2.0
\fBsched_yield\fP(2)	2.0
\fBsecurity\fP(2)		Not implemented
\fBselect\fP(2)
\fBsemctl\fP(2)
\fBsemget\fP(2)
\fBsemop\fP(2)
\fBsemtimedop\fP(2)	2.6; 2.4.22
\fBsend\fP(2)
\fBsendfile\fP(2)	2.2
\fBsendfile64\fP(2)	2.6; 2.4.19
\fBsendmsg\fP(2)
\fBsendto\fP(2)
\fBset_mempolicy\fP(2)	2.6.6
\fBset_robust_list\fP(2)	2.6.17
\fBset_thread_area\fP(2)	2.6
\fBset_tid_address\fP(2)	2.6
\fBset_zone_reclaim\fP(2)	2.6.13	Removed in 2.6.16 (was never
		available to userspace)
.\" See http://lkml.org/lkml/2005/8/1/83
.\" "[PATCH] remove sys_set_zone_reclaim()"
\fBsetdomainname\fP(2)
\fBsetfsgid\fP(2)	1.2
\fBsetfsgid32\fP(2)	2.4
\fBsetfsuid\fP(2)	1.2
\fBsetfsuid32\fP(2)	2.4
\fBsetgid\fP(2)
\fBsetgid32\fP(2)	2.4
\fBsetgroups\fP(2)
\fBsetgroups32\fP(2)	2.4
\fBsethostname\fP(2)
\fBsetitimer\fP(2)
\fBsetpgid\fP(2)
\fBsetpriority\fP(2)
\fBsetregid\fP(2)
\fBsetregid32\fP(2)	2.4
\fBsetresgid\fP(2)	2.2
\fBsetresgid32\fP(2)	2.4
\fBsetresuid\fP(2)	2.2
\fBsetresuid32\fP(2)	2.4
\fBsetreuid\fP(2)
\fBsetreuid32\fP(2)	2.4
\fBsetrlimit\fP(2)
\fBsetsid\fP(2)
\fBsetsockopt\fP(2)
\fBsettimeofday\fP(2)
\fBsetuid\fP(2)
\fBsetuid32\fP(2)	2.4
\fBsetup\fP(2)		Removed in 2.2
\fBsetxattr\fP(2)	2.6; 2.4.18
\fBsgetmask\fP(2)
\fBshmat\fP(2)
\fBshmctl\fP(2)
\fBshmdt\fP(2)
\fBshmget\fP(2)
\fBshutdown\fP(2)
\fBsigaction\fP(2)
\fBsigaltstack\fP(2)	2.2
\fBsignal\fP(2)
\fBsignalfd\fP(2)	2.6.22
\fBsignalfd4\fP(2)	2.6.27
\fBsigpending\fP(2)
\fBsigprocmask\fP(2)
\fBsigreturn\fP(2)
\fBsigsuspend\fP(2)
\fBsocket\fP(2)
\fBsocketcall\fP(2)
.\" Implements BSD socket calls
\fBsocketpair\fP(2)
\fBsplice\fP(2)	2.6.17
\fBspu_create\fP(2)	2.6.16	PowerPC only
\fBspu_run\fP(2)	2.6.16	PowerPC only
\fBssetmask\fP(2)
\fBstat\fP(2)
\fBstat64\fP(2)	2.4
\fBstatfs\fP(2)
\fBstatfs64\fP(2)	2.6
\fBstime\fP(2)
\fBstty\fP(2)		Not implemented
\fBswapoff\fP(2)
\fBswapon\fP(2)
\fBsymlink\fP(2)
\fBsymlinkat\fP(2)	2.6.16
\fBsync\fP(2)
\fBsync_file_range\fP(2)	2.6.17
.\" \fBsys_debug_setcontext\fP(2)	???	PowerPC if CONFIG_PPC32
\fBsysfs\fP(2)	1.2
\fBsysinfo\fP(2)
\fBsyslog\fP(2)
.\" glibc interface is \fBklogctl\fP(3)
\fBtee\fP(2)	2.6.17
\fBtgkill\fP(2)	2.6
\fBtime\fP(2)
\fBtimer_create\fP(2)	2.6
\fBtimer_delete\fP(2)	2.6
\fBtimer_getoverrun\fP(2)	2.6
\fBtimer_gettime\fP(2)	2.6
\fBtimer_settime\fP(2)	2.6
\fBtimerfd_create\fP(2)	2.6.25
\fBtimerfd_gettime\fP(2)	2.6.25
\fBtimerfd_settime\fP(2)	2.6.25
\fBtimes\fP(2)
\fBtkill\fP(2)	2.6; 2.4.22
\fBtruncate\fP(2)
\fBtruncate64\fP(2)	2.4
\fBtuxcall\fP(2)		Not implemented
.\" Unimplemented; no slot on i386
.\" As at 2.6.22, tuxcall has a slot on PowerPC, x86_64, and alpha
\fBugetrlimit\fP(2)	2.4
\fBulimit\fP(2)		Not implemented
.\" Implemented in glibc; see \fBulimit\fP(3)
\fBumask\fP(2)
\fBumount\fP(2)
.\" sys_oldumount() -- __NR_umount
\fBumount2\fP(2)	2.2
.\" sys_umount() -- __NR_umount2
\fBuname\fP(2)
\fBunlink\fP(2)
\fBunlinkat\fP(2)	2.6.16
\fBunshare\fP(2)	2.6.16
\fBuselib\fP(2)
\fBustat\fP(2)
\fButime\fP(2)
\fButimensat\fP(2)	2.6.22
\fButimes\fP(2)	2.2
\fBvfork\fP(2)
\fBvhangup\fP(2)
\fBvm86old\fP(2)
.\" Superseded by \fBvm86\fP(2)
\fBvmsplice\fP(2)	2.6.17
\fBvserver\fP(2)		Not implemented
\fBwait4\fP(2)
\fBwaitid\fP(2)	2.6.10
\fBwaitpid\fP(2)
\fBwrite\fP(2)
\fBwritev\fP(2)	2.0
.TE
.PP
On many platforms, including i386, socket calls are all multiplexed
(via glibc wrapper functions) through
.BR socketcall (2)
and similarly System V IPC calls are multiplexed through
.BR ipc (2).
.SH NOTES
Note the following points:
.IP * 3
Although slots are reserved for them in the system call table,
the following system calls are not implemented in the standard kernel:
.BR afs_syscall (2), \" __NR_afs_syscall is 53 on Linux 2.6.22/i386
.BR break (2),       \" __NR_break is 17 on Linux 2.6.22/i386
.BR ftime (2),       \" __NR_ftime is 35 on Linux 2.6.22/i386
.BR getpmsg (2),     \" __NR_getpmsg is 188 on Linux 2.6.22/i386
.BR gtty (2),        \" __NR_gtty is 32 on Linux 2.6.22/i386
.BR idle (2),        \" __NR_idle is 112 on Linux 2.6.22/i386
.BR lock (2),        \" __NR_lock is 53 on Linux 2.6.22/i386
.BR madvise1 (2),    \" __NR_madvise1 is 219 on Linux 2.6.22/i386
.BR mpx (2),         \" __NR_mpx is 66 on Linux 2.6.22/i386
.BR phys (2),        \" Slot has been reused
.BR prof (2),        \" __NR_prof is 44 on Linux 2.6.22/i386
.BR profil (2),      \" __NR_profil is 98 on Linux 2.6.22/i386
.BR putpmsg (2),     \" __NR_putpmsg is 189 on Linux 2.6.22/i386
.\" __NR_security is 223 on Linux 2.4/i386; absent on 2.6/i386, present
.\" on a couple of 2.6 architectures
.BR security (2),    \" __NR_security is 223 on Linux 2.4/i386
.BR stty (2),        \" __NR_stty is 31 on Linux 2.6.22/i386
.BR tuxcall (2),     \" __NR_tuxcall is 184 on x86_64, also on PPC and alpha
.BR ulimit (2),      \" __NR_ulimit is 58 on Linux 2.6.22/i386
and
.BR vserver (2)      \" __NR_vserver is 273 on Linux 2.6.22/i386
(see also
.BR unimplemented (2)).
However,
.BR ftime (3),
.BR profil (3)
and
.BR ulimit (3)
exist as library routines.
The slot for
.BR phys (2)
is in use since kernel 2.1.116 for
.BR umount (2);
.BR phys (2)
will never be implemented.
.IP *
The
.BR getpmsg (2)
and
.BR putpmsg (2)
calls are for kernels patched to support STREAMS,
and may never be in the standard kernel.
.\" The security call is for future use.
.PP
Roughly speaking, the code belonging to the system call
with number __NR_xxx defined in
.I /usr/include/asm/unistd.h
can be found in the kernel source in the routine
.IR sys_xxx ().
(The dispatch table for i386 can be found in
.IR /usr/src/linux/arch/i386/kernel/entry.S .)
There are many exceptions, however, mostly because
older system calls were superseded by newer ones,
and this has been treated somewhat unsystematically.
On platforms with
proprietary OS emulation, such as parisc, sparc, sparc64 and alpha,
there are many additional system calls; mips64 also contains a full
set of 32-bit system calls.

Over time, changes to the interfaces of some system calls have been
necessary.
One reason for such changes was the need to increase the size of
structures or scalar values passed to the system call.
Because of these changes, there are now various groups
of related system calls
(e.g.,
.BR truncate (2)
and
.BR truncate64 (2))
which perform similar tasks, but which vary in
details such as the size of their arguments.
(As noted earlier, applications are generally unaware of this:
the glibc wrapper functions do some work to ensure that the right
system call is invoked, and that ABI compatibility is
preserved for old binaries.)
Examples of systems calls that exist in multiple versions are
the following:
.IP * 3
By now there are three different versions of
.BR stat (2):
.IR sys_stat ()
(slot
.IR __NR_oldstat ),
.IR sys_newstat ()
(slot
.IR __NR_stat ),
and
.IR sys_stat64 ()
(slot
.IR __NR_stat64 ),
with the last being the most current.
.\" e.g., on 2.6.22/i386: __NR_oldstat 18, __NR_stat 106, __NR_stat64 195
.\" The stat system calls deal with three different data structures,
.\" defined in include/asm-i386/stat.h: __old_kernel_stat, stat, stat64
A similar story applies for
.BR lstat (2)
and
.BR fstat (2).
.IP *
Similarly, the defines
.IR __NR_oldolduname ,
.IR __NR_olduname ,
and
.I __NR_uname
refer to the routines
.IR sys_olduname (),
.IR sys_uname ()
and
.IR sys_newuname ().
.IP *
In Linux 2.0, a new version of
.BR vm86 (2)
appeared, with the old and the new kernel routines being named
.IR sys_vm86old ()
and
.IR sys_vm86 ().
.IP *
In Linux 2.4, a new version of
.BR getrlimit (2)
appeared, with the old and the new kernel routines being named
.IR sys_old_getrlimit ()
(slot
.IR __NR_getrlimit )
and
.IR sys_getrlimit ()
(slot
.IR __NR_ugetrlimit ).
.IP *
Linux 2.4 increased the size of user and group IDs from 16 to 32 bits.
.\" 64 bit off_t changes: ftruncate64, *stat64,
.\" fcntl64 (because of the flock structure), getdents64, *statfs64
To support this change, a range of system calls were added
(e.g.,
.BR chown32 (2),
.BR getuid32 (2),
.BR getgroups32 (2),
.BR setresuid32 (2)),
superseding earlier calls of the same name without the
"32" suffix.
.IP *
Linux 2.4 added support for applications on 32-bit architectures
to access large files (i.e., files for which the sizes and
file offsets can't be represented in 32 bits.)
To support this change, replacements were required for system calls
that deal with file offsets and sizes.
Thus the following system calls were added:
.BR fcntl64 (2),
.BR ftruncate64 (2),
.BR getdents64 (2),
.BR stat64 (2),
.BR statfs64 (2),
and their analogs that work with file descriptors or
symbolic links.
These system calls supersede the older system calls
which, except in the case of the "stat" calls,
have the same name without the "64" suffix.

On newer platforms that only have 64-bit file access and 32-bit uids
(e.g., alpha, ia64, s390x) there are no *64 or *32 calls.
Where the *64 and *32 calls exist, the other versions are obsolete.
.IP *
The
.I rt_sig*
calls were added in kernel 2.2 to support the addition
of real-time signals (see
.BR signal (7)).
These system calls supersede the older system calls of the same
name without the "rt_" prefix.
.IP *
The
.BR select (2)
and
.BR mmap (2)
system calls use five or more arguments,
which caused problems the way
argument passing on the i386 used to be set up.
Thus, while other architectures have
.IR sys_select ()
and
.IR sys_mmap ()
corresponding to
.I __NR_select
and
.IR __NR_mmap ,
on i386 one finds
.IR old_select ()
and
.IR old_mmap ()
(routines that use a pointer to a
argument block) instead.
These days passing five arguments
is not a problem any more, and there is a
.I __NR__newselect
.\" (used by libc 6)
that corresponds directly to
.IR sys_select ()
and similarly
.IR __NR_mmap2 .
.\" .PP
.\" Two system call numbers,
.\" .IR __NR__llseek
.\" and
.\" .IR __NR__sysctl
.\" have an additional underscore absent in
.\" .IR sys_llseek ()
.\" and
.\" .IR sys_sysctl ().
.\"
.\" In kernel 2.1.81,
.\" .BR lchown (2)
.\" and
.\" .BR chown (2)
.\" were swapped; that is,
.\" .BR lchown (2)
.\" was added with the semantics that were then current for
.\" .BR chown (2),
.\" and the semantics of the latter call were changed to what
.\" they are today.
.SH SEE ALSO
.BR syscall (2),
.BR unimplemented (2),
.BR libc (7)
.SH COLOPHON
This page is part of release 3.27 of the Linux
.I man-pages
project.
A description of the project,
and information about reporting bugs,
can be found at
http://www.kernel.org/doc/man-pages/.