1SYSCALLS(2) Linux Programmer's Manual SYSCALLS(2)
2
6 syscalls - Linux system calls
7
9 Linux system calls.
10
12 The system call is the fundamental interface between an application and
13 the Linux kernel.
14 System calls and library wrapper functions
16 System calls are generally not invoked directly, but rather via wrapper
17 functions in glibc (or perhaps some other library). For details of
18 direct invocation of a system call, see intro(2). Often, but not
19 always, the name of the wrapper function is the same as the name of the
20 system call that it invokes. For example, glibc contains a function
21 truncate() which invokes the underlying "truncate" system call.
22 Often the glibc wrapper function is quite thin, doing little work other
24 than copying arguments to the right registers before invoking the sys‐
25 tem call, and then setting errno appropriately after the system call
26 has returned. (These are the same steps that are performed by
27 syscall(2), which can be used to invoke system calls for which no wrap‐
28 per function is provided.) Note: system calls indicate a failure by
29 returning a negative error number to the caller; when this happens, the
30 wrapper function negates the returned error number (to make it posi‐
31 tive), copies it to errno, and returns -1 to the caller of the wrapper.
32 Sometimes, however, the wrapper function does some extra work before
34 invoking the system call. For example, nowadays there are (for reasons
35 described below) two related system calls, truncate(2) and trun‐
36 cate64(2), and the glibc truncate() wrapper function checks which of
37 those system calls are provided by the kernel and determines which
38 should be employed.
39 System call list
41 Below is a list of those system calls that are common to most plat‐
42 forms. In the list, the Kernel column indicates the kernel version for
43 those system calls that were new in Linux 2.2, or have appeared since
44 that kernel version. Note the following points:
45 * Where no kernel version is indicated, the system call appeared in
47 kernel 1.0 or earlier.
48 * Where a system call is marked "1.2" this means the system call prob‐
50 ably appeared in a 1.1.x kernel version, and first appeared in a
51 stable kernel with 1.2. (Development of the 1.2 kernel was initi‐
52 ated from a branch of kernel 1.0.6 via the 1.1.x unstable kernel
53 series.)
54 * Where a system call is marked "2.0" this means the system call prob‐
56 ably appeared in a 1.3.x kernel version, and first appeared in a
57 stable kernel with 2.0. (Development of the 2.0 kernel was initi‐
58 ated from a branch of kernel 1.2.x, somewhere around 1.2.10, via the
59 1.3.x unstable kernel series.)
60 * Where a system call is marked "2.2" this means the system call prob‐
62 ably appeared in a 2.1.x kernel version, and first appeared in a
63 stable kernel with 2.2.0. (Development of the 2.2 kernel was initi‐
64 ated from a branch of kernel 2.0.21 via the 2.1.x unstable kernel
65 series.)
66 * Where a system call is marked "2.4" this means the system call prob‐
68 ably appeared in a 2.3.x kernel version, and first appeared in a
69 stable kernel with 2.4.0. (Development of the 2.4 kernel was initi‐
70 ated from a branch of kernel 2.2.8 via the 2.3.x unstable kernel
71 series.)
72 * Where a system call is marked "2.6" this means the system call prob‐
74 ably appeared in a 2.5.x kernel version, and first appeared in a
75 stable kernel with 2.6.0. (Development of kernel 2.6 was initiated
76 from a branch of kernel 2.4.15 via the 2.5.x unstable kernel
77 series.)
78 * Starting with kernel 2.6.0, the development model changed, and new
80 system calls may appear in each 2.6.x release. In this case, the
81 exact version number where the system call appeared is shown.
82 * In some cases, a system call was added to a stable kernel series
84 after it branched from the previous stable kernel series, and then
85 backported into the earlier stable kernel series. For example some
86 system calls that appeared in 2.6.x were also backported into a
87 2.4.x release after 2.4.15. When this is so, the version where the
88 system call appeared in both of the major kernel series is listed.
89 The list of system calls that are available as at kernel 2.6.33 (or in
91 a few cases only on older kernels) is as follows:
92 System call Kernel Notes
94 ─────────────────────────────────────────────────────────────────────────
95 _llseek(2) 1.2
97 _newselect(2)
98 _sysctl(2)
99 accept(2)
100 accept4(2) 2.6.28
101 access(2)
102 acct(2)
103 add_key(2) 2.6.11
104 adjtimex(2)
105 afs_syscall(2) Not implemented
106 alarm(2)
107 alloc_hugepages(2) 2.5.36 Removed in 2.5.44
108 bdflush(2)
109 bind(2)
110 break(2) Not implemented
111 brk(2)
112 cacheflush(2) 1.2 Not on i386
113 capget(2) 2.2
114 capset(2) 2.2
115 chdir(2)
116 chmod(2)
117 chown(2)
118 chown32(2) 2.4
119 chroot(2)
120 clock_getres(2) 2.6
121 clock_gettime(2) 2.6
122 clock_nanosleep(2) 2.6
123 clock_settime(2) 2.6
124 clone(2)
125 close(2)
126 connect(2)
127 creat(2)
128 create_module(2)
129 delete_module(2)
130 dup(2)
131 dup2(2)
132 dup3(2) 2.6.27
134 epoll_create(2) 2.6
135 epoll_create1(2) 2.6.27
136 epoll_ctl(2) 2.6
137 epoll_pwait(2) 2.6.19
138 epoll_wait(2) 2.6
139 eventfd(2) 2.6.22
140 eventfd2(2) 2.6.27
141 execve(2)
142 exit(2)
143 exit_group(2) 2.6
144 faccessat(2) 2.6.16
145 fadvise64(2) 2.6
146 fadvise64_64(2) 2.6
147 fallocate(2) 2.6.23
148 fchdir(2)
149 fchmod(2)
150 fchmodat(2) 2.6.16
151 fchown(2)
152 fchown32(2) 2.4
153 fchownat(2) 2.6.16
154 fcntl(2)
155 fcntl64(2) 2.4
156 fdatasync(2)
157 fgetxattr(2) 2.6; 2.4.18
158 flistxattr(2) 2.6; 2.4.18
159 flock(2) 2.0
160 fork(2)
161 free_hugepages(2) 2.5.36 Removed in 2.5.44
162 fremovexattr(2) 2.6; 2.4.18
163 fsetxattr(2) 2.6; 2.4.18
164 fstat(2)
165 fstat64(2) 2.4
166 fstatat64(2) 2.6.16
167 fstatfs(2)
168 fstatfs64(2) 2.6
169 fsync(2)
170 ftime(2) Not implemented
171 ftruncate(2)
172 ftruncate64(2) 2.4
173 futex(2) 2.6
174 futimesat(2) 2.6.16
175 get_kernel_syms(2)
176 get_mempolicy(2) 2.6.6
177 get_robust_list(2) 2.6.17
178 get_thread_area(2) 2.6
179 getcpu(2) 2.6.19
180 getcwd(2) 2.2
181 getdents(2) 2.0
182 getdents64(2) 2.4
183 getegid(2)
184 getegid32(2) 2.4
185 geteuid(2)
186 geteuid32(2) 2.4
187 getgid(2)
188 getgid32(2) 2.4
189 getgroups(2)
190 getgroups32(2) 2.4
191 getitimer(2)
192 getpeername(2)
193 getpagesize(2) 2.0 Not on i386
194 getpgid(2)
195 getpgrp(2)
196 getpid(2)
197 getpmsg(2) Not implemented
198 getppid(2)
200 getpriority(2)
201 getresgid(2) 2.2
202 getresgid32(2) 2.4
203 getresuid(2) 2.2
204 getresuid32(2) 2.4
205 getrlimit(2)
206 getrusage(2)
207 getsid(2) 2.0
208 getsockname(2)
209 getsockopt(2)
210 gettid(2) 2.4.11
211 gettimeofday(2)
212 getuid(2)
213 getuid32(2) 2.4
214 getxattr(2) 2.6; 2.4.18
215 gtty(2) Not implemented
216 idle(2) Not implemented
217 init_module(2)
218 inotify_add_watch(2) 2.6.13
219 inotify_init(2) 2.6.13
220 inotify_init1(2) 2.6.27
221 inotify_rm_watch(2) 2.6.13
222 io_cancel(2) 2.6
223 io_destroy(2) 2.6
224 io_getevents(2) 2.6
225 io_setup(2) 2.6
226 io_submit(2) 2.6
227 ioctl(2)
228 ioperm(2)
229 iopl(2)
230 ioprio_get(2) 2.6.13
231 ioprio_set(2) 2.6.13
232 ipc(2)
233 kexec_load(2) 2.6.7
234 keyctl(2) 2.6.11
235 kill(2)
236 lchown(2) 2.2
237 lchown32(2) 2.4
238 lgetxattr(2) 2.6; 2.4.18
239 link(2)
240 linkat(2) 2.6.16
241 listen(2)
242 listxattr(2) 2.6; 2.4.18
243 llistxattr(2) 2.6; 2.4.18
244 lock(2) Not implemented
245 lookup_dcookie(2) 2.6
246 lremovexattr(2) 2.6; 2.4.18
247 lseek(2)
248 lsetxattr(2) 2.6; 2.4.18
249 lstat(2)
250 lstat64(2) 2.4
251 madvise(2) 2.4
252 madvise1(2) 2.4
253 mbind(2) 2.6.6
254 migrate_pages(2) 2.6.16
255 mincore(2) 2.4
256 mkdir(2)
257 mkdirat(2) 2.6.16
258 mknod(2)
259 mknodat(2) 2.6.16
260 mlock(2)
261 mlockall(2)
262 mmap(2)
263 mmap2(2) 2.4
264 modify_ldt(2)
266 mount(2)
267 move_pages(2) 2.6.18
268 mprotect(2)
269 mpx(2) Not implemented
270 mq_getsetattr(2) 2.6.6
271 mq_notify(2) 2.6.6
272 mq_open(2) 2.6.6
273 mq_timedreceive(2) 2.6.6
274 mq_timedsend(2) 2.6.6
275 mq_unlink(2)
276 mremap(2) 2.0
277 msgctl(2)
278 msgget(2)
279 msgrcv(2)
280 msgsnd(2)
281 msync(2) 2.0
282 munlock(2)
283 munlockall(2)
284 munmap(2)
285 nanosleep(2) 2.0
286 nfsservctl(2) 2.2
287 nice(2)
288 oldfstat(2)
289 oldlstat(2)
290 oldolduname(2)
291 oldstat(2)
292 olduname(2)
293 open(2)
294 openat(2) 2.6.16
295 pause(2)
296 pciconfig_iobase(2) 2.2.15; 2.4 Not on i386
297 pciconfig_read(2) 2.0.26; 2.2 Not on i386
298 pciconfig_write(2) 2.0.26; 2.2 Not on i386
299 perf_event_open(2) 2.6.31 Was called perf_counter_open()
300 in 2.6.31; renamed in 2.6.32
301 personality(2) 1.2
302 phys(2) Not implemented
303 pipe(2)
304 pipe2(2) 2.6.27
305 pivot_root(2) 2.4
306 poll(2) 2.2
307 ppoll(2) 2.6.16
308 prctl(2) 2.2
309 pread64(2) Added as "pread" in 2.2;
310 renamed "pread64" in 2.6
311 preadv(2) 2.6.30
312 prof(2) Not implemented
313 profil(2) Not implemented
314 pselect6(2) 2.6.16
315 ptrace(2)
316 putpmsg(2) Not implemented
317 pwrite64(2) Added as "pwrite" in 2.2;
318 renamed "pwrite64" in 2.6
319 pwritev(2) 2.6.30
320 query_module(2) 2.2
321 quotactl(2)
322 read(2)
323 readahead(2) 2.4.13
324 readdir(2)
325 readlink(2)
326 readlinkat(2) 2.6.16
327 readv(2) 2.0
328 reboot(2)
329 recv(2)
330 recvfrom(2)
332 recvmsg(2)
333 recvmmsg(2) 2.6.33
334 remap_file_pages(2) 2.6
335 removexattr(2) 2.6; 2.4.18
336 rename(2)
337 renameat(2) 2.6.16
338 request_key(2) 2.6.11
339 restart_syscall(2) 2.6
340 rmdir(2)
341 rt_sigaction(2) 2.2
342 rt_sigpending(2) 2.2
343 rt_sigprocmask(2) 2.2
344 rt_sigqueueinfo(2) 2.2
345 rt_sigreturn(2) 2.2
346 rt_sigsuspend(2) 2.2
347 rt_sigtimedwait(2) 2.2
348 rt_tgsigqueueinfo(2) 2.6.31
349 sched_get_priority_max(2) 2.0
350 sched_get_priority_min(2) 2.0
351 sched_getaffinity(2) 2.6
352 sched_getparam(2) 2.0
353 sched_getscheduler(2) 2.0
354 sched_rr_get_interval(2) 2.0
355 sched_setaffinity(2) 2.6
356 sched_setparam(2) 2.0
357 sched_setscheduler(2) 2.0
358 sched_yield(2) 2.0
359 security(2) Not implemented
360 select(2)
361 semctl(2)
362 semget(2)
363 semop(2)
364 semtimedop(2) 2.6; 2.4.22
365 send(2)
366 sendfile(2) 2.2
367 sendfile64(2) 2.6; 2.4.19
368 sendmsg(2)
369 sendto(2)
370 set_mempolicy(2) 2.6.6
371 set_robust_list(2) 2.6.17
372 set_thread_area(2) 2.6
373 set_tid_address(2) 2.6
374 set_zone_reclaim(2) 2.6.13 Removed in 2.6.16 (was never
375 available to userspace)
376 setdomainname(2)
377 setfsgid(2) 1.2
378 setfsgid32(2) 2.4
379 setfsuid(2) 1.2
380 setfsuid32(2) 2.4
381 setgid(2)
382 setgid32(2) 2.4
383 setgroups(2)
384 setgroups32(2) 2.4
385 sethostname(2)
386 setitimer(2)
387 setpgid(2)
388 setpriority(2)
389 setregid(2)
390 setregid32(2) 2.4
391 setresgid(2) 2.2
392 setresgid32(2) 2.4
393 setresuid(2) 2.2
394 setresuid32(2) 2.4
395 setreuid(2)
396 setreuid32(2) 2.4
398 setrlimit(2)
399 setsid(2)
400 setsockopt(2)
401 settimeofday(2)
402 setuid(2)
403 setuid32(2) 2.4
404 setup(2) Removed in 2.2
405 setxattr(2) 2.6; 2.4.18
406 sgetmask(2)
407 shmat(2)
408 shmctl(2)
409 shmdt(2)
410 shmget(2)
411 shutdown(2)
412 sigaction(2)
413 sigaltstack(2) 2.2
414 signal(2)
415 signalfd(2) 2.6.22
416 signalfd4(2) 2.6.27
417 sigpending(2)
418 sigprocmask(2)
419 sigreturn(2)
420 sigsuspend(2)
421 socket(2)
422 socketcall(2)
423 socketpair(2)
424 splice(2) 2.6.17
425 spu_create(2) 2.6.16 PowerPC only
426 spu_run(2) 2.6.16 PowerPC only
427 ssetmask(2)
428 stat(2)
429 stat64(2) 2.4
430 statfs(2)
431 statfs64(2) 2.6
432 stime(2)
433 stty(2) Not implemented
434 swapoff(2)
435 swapon(2)
436 symlink(2)
437 symlinkat(2) 2.6.16
438 sync(2)
439 sync_file_range(2) 2.6.17
440 sysfs(2) 1.2
441 sysinfo(2)
442 syslog(2)
443 tee(2) 2.6.17
444 tgkill(2) 2.6
445 time(2)
446 timer_create(2) 2.6
447 timer_delete(2) 2.6
448 timer_getoverrun(2) 2.6
449 timer_gettime(2) 2.6
450 timer_settime(2) 2.6
451 timerfd_create(2) 2.6.25
452 timerfd_gettime(2) 2.6.25
453 timerfd_settime(2) 2.6.25
454 times(2)
455 tkill(2) 2.6; 2.4.22
456 truncate(2)
457 truncate64(2) 2.4
458 tuxcall(2) Not implemented
459 ugetrlimit(2) 2.4
460 ulimit(2) Not implemented
461 umask(2)
462 umount(2)
464 umount2(2) 2.2
465 uname(2)
466 unlink(2)
467 unlinkat(2) 2.6.16
468 unshare(2) 2.6.16
469 uselib(2)
470 ustat(2)
471 utime(2)
472 utimensat(2) 2.6.22
473 utimes(2) 2.2
474 vfork(2)
475 vhangup(2)
476 vm86old(2)
477 vmsplice(2) 2.6.17
478 vserver(2) Not implemented
479 wait4(2)
480 waitid(2) 2.6.10
481 waitpid(2)
482 write(2)
483 writev(2) 2.0
484 On many platforms, including i386, socket calls are all multiplexed
486 (via glibc wrapper functions) through socketcall(2) and similarly Sys‐
487 tem V IPC calls are multiplexed through ipc(2).
488
490 Note the following points:
491 * Although slots are reserved for them in the system call table, the
493 following system calls are not implemented in the standard kernel:
494 afs_syscall(2), break(2), ftime(2), getpmsg(2), gtty(2), idle(2),
495 lock(2), madvise1(2), mpx(2), phys(2), prof(2), profil(2),
496 putpmsg(2), security(2), stty(2), tuxcall(2), ulimit(2), and
497 vserver(2) (see also unimplemented(2)). However, ftime(3), pro‐
498 fil(3) and ulimit(3) exist as library routines. The slot for
499 phys(2) is in use since kernel 2.1.116 for umount(2); phys(2) will
500 never be implemented.
501 * The getpmsg(2) and putpmsg(2) calls are for kernels patched to sup‐
503 port STREAMS, and may never be in the standard kernel.
504 Roughly speaking, the code belonging to the system call with number
506 __NR_xxx defined in /usr/include/asm/unistd.h can be found in the ker‐
507 nel source in the routine sys_xxx(). (The dispatch table for i386 can
508 be found in /usr/src/linux/arch/i386/kernel/entry.S.) There are many
509 exceptions, however, mostly because older system calls were superseded
510 by newer ones, and this has been treated somewhat unsystematically. On
511 platforms with proprietary OS emulation, such as parisc, sparc, sparc64
512 and alpha, there are many additional system calls; mips64 also contains
513 a full set of 32-bit system calls.
514 Over time, changes to the interfaces of some system calls have been
516 necessary. One reason for such changes was the need to increase the
517 size of structures or scalar values passed to the system call. Because
518 of these changes, there are now various groups of related system calls
519 (e.g., truncate(2) and truncate64(2)) which perform similar tasks, but
520 which vary in details such as the size of their arguments. (As noted
521 earlier, applications are generally unaware of this: the glibc wrapper
522 functions do some work to ensure that the right system call is invoked,
523 and that ABI compatibility is preserved for old binaries.) Examples of
524 systems calls that exist in multiple versions are the following:
525 * By now there are three different versions of stat(2): sys_stat()
527 (slot __NR_oldstat), sys_newstat() (slot __NR_stat), and
528 sys_stat64() (slot __NR_stat64), with the last being the most cur‐
529 rent. A similar story applies for lstat(2) and fstat(2).
530 * Similarly, the defines __NR_oldolduname, __NR_olduname, and
532 __NR_uname refer to the routines sys_olduname(), sys_uname() and
533 sys_newuname().
534 * In Linux 2.0, a new version of vm86(2) appeared, with the old and
536 the new kernel routines being named sys_vm86old() and sys_vm86().
537 * In Linux 2.4, a new version of getrlimit(2) appeared, with the old
539 and the new kernel routines being named sys_old_getrlimit() (slot
540 __NR_getrlimit) and sys_getrlimit() (slot __NR_ugetrlimit).
541 * Linux 2.4 increased the size of user and group IDs from 16 to 32
543 bits. To support this change, a range of system calls were added
544 (e.g., chown32(2), getuid32(2), getgroups32(2), setresuid32(2)),
545 superseding earlier calls of the same name without the "32" suffix.
546 * Linux 2.4 added support for applications on 32-bit architectures to
548 access large files (i.e., files for which the sizes and file offsets
549 can't be represented in 32 bits.) To support this change, replace‐
550 ments were required for system calls that deal with file offsets and
551 sizes. Thus the following system calls were added: fcntl64(2),
552 ftruncate64(2), getdents64(2), stat64(2), statfs64(2), and their
553 analogs that work with file descriptors or symbolic links. These
554 system calls supersede the older system calls which, except in the
555 case of the "stat" calls, have the same name without the "64" suf‐
556 fix.
557 On newer platforms that only have 64-bit file access and 32-bit uids
559 (e.g., alpha, ia64, s390x) there are no *64 or *32 calls. Where the
560 *64 and *32 calls exist, the other versions are obsolete.
561 * The rt_sig* calls were added in kernel 2.2 to support the addition
563 of real-time signals (see signal(7)). These system calls supersede
564 the older system calls of the same name without the "rt_" prefix.
565 * The select(2) and mmap(2) system calls use five or more arguments,
567 which caused problems the way argument passing on the i386 used to
568 be set up. Thus, while other architectures have sys_select() and
569 sys_mmap() corresponding to __NR_select and __NR_mmap, on i386 one
570 finds old_select() and old_mmap() (routines that use a pointer to a
571 argument block) instead. These days passing five arguments is not a
572 problem any more, and there is a __NR__newselect that corresponds
573 directly to sys_select() and similarly __NR_mmap2.
574
576 syscall(2), unimplemented(2), libc(7)
577
579 This page is part of release 3.25 of the Linux man-pages project. A
580 description of the project, and information about reporting bugs, can
581 be found at http://www.kernel.org/doc/man-pages/.
582Linux 2010-03-06 SYSCALLS(2)