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 chdir() which invokes the underlying "chdir" 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 on architectures with‐
30 out a separate error register/flag, as noted in syscall(2); when this
31 happens, the wrapper function negates the returned error number (to
32 make it positive), copies it to errno, and returns -1 to the caller of
33 the wrapper.
34 Sometimes, however, the wrapper function does some extra work before
36 invoking the system call. For example, nowadays there are (for reasons
37 described below) two related system calls, truncate(2) and trun‐
38 cate64(2), and the glibc truncate() wrapper function checks which of
39 those system calls are provided by the kernel and determines which
40 should be employed.
41 System call list
43 Below is a list of the Linux system calls. In the list, the Kernel
44 column indicates the kernel version for those system calls that were
45 new in Linux 2.2, or have appeared since that kernel version. Note the
46 following points:
47 * Where no kernel version is indicated, the system call appeared in
49 kernel 1.0 or earlier.
50 * Where a system call is marked "1.2" this means the system call prob‐
52 ably appeared in a 1.1.x kernel version, and first appeared in a
53 stable kernel with 1.2. (Development of the 1.2 kernel was initi‐
54 ated from a branch of kernel 1.0.6 via the 1.1.x unstable kernel
55 series.)
56 * Where a system call is marked "2.0" this means the system call prob‐
58 ably appeared in a 1.3.x kernel version, and first appeared in a
59 stable kernel with 2.0. (Development of the 2.0 kernel was initi‐
60 ated from a branch of kernel 1.2.x, somewhere around 1.2.10, via the
61 1.3.x unstable kernel series.)
62 * Where a system call is marked "2.2" this means the system call prob‐
64 ably appeared in a 2.1.x kernel version, and first appeared in a
65 stable kernel with 2.2.0. (Development of the 2.2 kernel was initi‐
66 ated from a branch of kernel 2.0.21 via the 2.1.x unstable kernel
67 series.)
68 * Where a system call is marked "2.4" this means the system call prob‐
70 ably appeared in a 2.3.x kernel version, and first appeared in a
71 stable kernel with 2.4.0. (Development of the 2.4 kernel was initi‐
72 ated from a branch of kernel 2.2.8 via the 2.3.x unstable kernel
73 series.)
74 * Where a system call is marked "2.6" this means the system call prob‐
76 ably appeared in a 2.5.x kernel version, and first appeared in a
77 stable kernel with 2.6.0. (Development of kernel 2.6 was initiated
78 from a branch of kernel 2.4.15 via the 2.5.x unstable kernel
79 series.)
80 * Starting with kernel 2.6.0, the development model changed, and new
82 system calls may appear in each 2.6.x release. In this case, the
83 exact version number where the system call appeared is shown. This
84 convention continues with the 3.x kernel series, which followed on
85 from kernel 2.6.39, and the 4.x kernel series, which followed on
86 from kernel 3.19.
87 * In some cases, a system call was added to a stable kernel series
89 after it branched from the previous stable kernel series, and then
90 backported into the earlier stable kernel series. For example some
91 system calls that appeared in 2.6.x were also backported into a
92 2.4.x release after 2.4.15. When this is so, the version where the
93 system call appeared in both of the major kernel series is listed.
94 The list of system calls that are available as at kernel 4.19 (or in a
96 few cases only on older kernels) is as follows:
97 System call Kernel Notes
99 ───────────────────────────────────────────────────────────────────────
100 _llseek(2) 1.2
102 _newselect(2) 2.0
103 _sysctl(2) 2.0
104 accept(2) 2.0 See notes on socketcall(2)
105 accept4(2) 2.6.28
106 access(2) 1.0
107 acct(2) 1.0
108 add_key(2) 2.6.10
109 adjtimex(2) 1.0
110 alarm(2) 1.0
111 alloc_hugepages(2) 2.5.36 Removed in 2.5.44
112 arc_gettls(2) 3.9 ARC only
113 arc_settls(2) 3.9 ARC only
114 arc_usr_cmpxchg(2) 4.9 ARC only
115 arch_prctl(2) 2.6 x86_64, x86 since 4.12
116 atomic_barrier(2) 2.6.34 m68k only
117 atomic_cmpxchg_32(2) 2.6.34 m68k only
118 bdflush(2) 1.2 Deprecated (does nothing)
119 since 2.6
120 bfin_spinlock(2) 2.6.22 Blackfin only (port removed
121 in Linux 4.17)
122 bind(2) 2.0 See notes on socketcall(2)
123 bpf(2) 3.18
124 brk(2) 1.0
125 breakpoint(2) 2.2 ARM OABI only, defined with
126 __ARM_NR prefix
127 cacheflush(2) 1.2 Not on x86
128 capget(2) 2.2
129 capset(2) 2.2
130 chdir(2) 1.0
131 chmod(2) 1.0
132 chown(2) 2.2 See chown(2) for
134 version details
135 chown32(2) 2.4
136 chroot(2) 1.0
137 clock_adjtime(2) 2.6.39
138 clock_getres(2) 2.6
139 clock_gettime(2) 2.6
140 clock_nanosleep(2) 2.6
141 clock_settime(2) 2.6
142 clone2(2) 2.4 IA-64 only
143 clone(2) 1.0
144 close(2) 1.0
145 cmpxchg_badaddr(2) 2.6.36 Tile only (port removed
146 in Linux 4.17)
147 connect(2) 2.0 See notes on socketcall(2)
148 copy_file_range(2) 4.5
149 creat(2) 1.0
150 create_module(2) 1.0 Removed in 2.6
151 delete_module(2) 1.0
152 dma_memcpy(2) 2.6.22 Blackfin only (port removed
153 in Linux 4.17)
154 dup(2) 1.0
155 dup2(2) 1.0
156 dup3(2) 2.6.27
157 epoll_create(2) 2.6
158 epoll_create1(2) 2.6.27
159 epoll_ctl(2) 2.6
160 epoll_pwait(2) 2.6.19
161 epoll_wait(2) 2.6
162 eventfd(2) 2.6.22
163 eventfd2(2) 2.6.27
164 execv(2) 2.0 SPARC/SPARC64 only, for
165 compatibility with SunOS
166 execve(2) 1.0
167 execveat(2) 3.19
168 exit(2) 1.0
169 exit_group(2) 2.6
170 faccessat(2) 2.6.16
171 fadvise64(2) 2.6
172 fadvise64_64(2) 2.6
173 fallocate(2) 2.6.23
174 fanotify_init(2) 2.6.37
175 fanotify_mark(2) 2.6.37
176 fchdir(2) 1.0
177 fchmod(2) 1.0
178 fchmodat(2) 2.6.16
179 fchown(2) 1.0
180 fchown32(2) 2.4
181 fchownat(2) 2.6.16
182 fcntl(2) 1.0
183 fcntl64(2) 2.4
184 fdatasync(2) 2.0
185 fgetxattr(2) 2.6; 2.4.18
186 finit_module(2) 3.8
187 flistxattr(2) 2.6; 2.4.18
188 flock(2) 2.0
189 fork(2) 1.0
190 free_hugepages(2) 2.5.36 Removed in 2.5.44
191 fremovexattr(2) 2.6; 2.4.18
192 fsetxattr(2) 2.6; 2.4.18
193 fstat(2) 1.0
194 fstat64(2) 2.4
195 fstatat64(2) 2.6.16
196 fstatfs(2) 1.0
197 fstatfs64(2) 2.6
198 fsync(2) 1.0
200 ftruncate(2) 1.0
201 ftruncate64(2) 2.4
202 futex(2) 2.6
203 futimesat(2) 2.6.16
204 get_kernel_syms(2) 1.0 Removed in 2.6
205 get_mempolicy(2) 2.6.6
206 get_robust_list(2) 2.6.17
207 get_thread_area(2) 2.6
208 get_tls(2) 4.15 ARM OABI only, has
209 __ARM_NR prefix
210 getcpu(2) 2.6.19
211 getcwd(2) 2.2
212 getdents(2) 2.0
213 getdents64(2) 2.4
214 getdomainname(2) 2.2 SPARC, SPARC64; available
215 as osf_getdomainname(2)
216 on Alpha since Linux 2.0
217 getdtablesize(2) 2.0 SPARC (removed in 2.6.26),
218 available since Linux 2.0 on
219 Alpha as osf_getdtablesize(2)
220 getegid(2) 1.0
221 getegid32(2) 2.4
222 geteuid(2) 1.0
223 geteuid32(2) 2.4
224 getgid(2) 1.0
225 getgid32(2) 2.4
226 getgroups(2) 1.0
227 getgroups32(2) 2.4
228 gethostname(2) 2.0 Alpha, was available on
229 SPARC up to Linux 2.6.26
230 getitimer(2) 1.0
231 getpeername(2) 2.0 See notes on socketcall(2)
232 getpagesize(2) 2.0 Not on x86
233 getpgid(2) 1.0
234 getpgrp(2) 1.0
235 getpid(2) 1.0
236 getppid(2) 1.0
237 getpriority(2) 1.0
238 getrandom(2) 3.17
239 getresgid(2) 2.2
240 getresgid32(2) 2.4
241 getresuid(2) 2.2
242 getresuid32(2) 2.4
243 getrlimit(2) 1.0
244 getrusage(2) 1.0
245 getsid(2) 2.0
246 getsockname(2) 2.0 See notes on socketcall(2)
247 getsockopt(2) 2.0 See notes on socketcall(2)
248 gettid(2) 2.4.11
249 gettimeofday(2) 1.0
250 getuid(2) 1.0
251 getuid32(2) 2.4
252 getunwind(2) 2.4.8 IA-64 only; deprecated
253 getxattr(2) 2.6; 2.4.18
254 getxgid(2) 2.0 Alpha only; see NOTES
255 getxpid(2) 2.0 Alpha only; see NOTES
256 getxuid(2) 2.0 Alpha only; see NOTES
257 init_module(2) 1.0
258 inotify_add_watch(2) 2.6.13
259 inotify_init(2) 2.6.13
260 inotify_init1(2) 2.6.27
261 inotify_rm_watch(2) 2.6.13
262 io_cancel(2) 2.6
263 io_destroy(2) 2.6
264 io_getevents(2) 2.6
266 io_pgetevents(2) 4.18
267 io_setup(2) 2.6
268 io_submit(2) 2.6
269 ioctl(2) 1.0
270 ioperm(2) 1.0
271 iopl(2) 1.0
272 ioprio_get(2) 2.6.13
273 ioprio_set(2) 2.6.13
274 ipc(2) 1.0
275 kcmp(2) 3.5
276 kern_features(2) 3.7 SPARC64 only
277 kexec_file_load(2) 3.17
278 kexec_load(2) 2.6.13
279 keyctl(2) 2.6.10
280 kill(2) 1.0
281 lchown(2) 1.0 See chown(2) for
282 version details
283 lchown32(2) 2.4
284 lgetxattr(2) 2.6; 2.4.18
285 link(2) 1.0
286 linkat(2) 2.6.16
287 listen(2) 2.0 See notes on socketcall(2)
288 listxattr(2) 2.6; 2.4.18
289 llistxattr(2) 2.6; 2.4.18
290 lookup_dcookie(2) 2.6
291 lremovexattr(2) 2.6; 2.4.18
292 lseek(2) 1.0
293 lsetxattr(2) 2.6; 2.4.18
294 lstat(2) 1.0
295 lstat64(2) 2.4
296 madvise(2) 2.4
297 mbind(2) 2.6.6
298 memory_ordering(2) 2.2 SPARC64 only
299 metag_get_tls(2) 3.9 Metag only (port removed
300 in Linux 4.17)
301 metag_set_fpu_flags(2) 3.9 Metag only (port removed
302 in Linux 4.17)
303 metag_set_tls(2) 3.9 Metag only (port removed
304 in Linux 4.17)
305 metag_setglobalbit(2) 3.9 Metag only (port removed
306 in Linux 4.17)
307 membarrier(2) 3.17
308 memfd_create(2) 3.17
309 migrate_pages(2) 2.6.16
310 mincore(2) 2.4
311 mkdir(2) 1.0
312 mkdirat(2) 2.6.16
313 mknod(2) 1.0
314 mknodat(2) 2.6.16
315 mlock(2) 2.0
316 mlock2(2) 4.4
317 mlockall(2) 2.0
318 mmap(2) 1.0
319 mmap2(2) 2.4
320 modify_ldt(2) 1.0
321 mount(2) 1.0
322 move_pages(2) 2.6.18
323 mprotect(2) 1.0
324 mq_getsetattr(2) 2.6.6
325 mq_notify(2) 2.6.6
326 mq_open(2) 2.6.6
327 mq_timedreceive(2) 2.6.6
328 mq_timedsend(2) 2.6.6
329 mq_unlink(2) 2.6.6
330 mremap(2) 2.0
332 msgctl(2) 2.0 See notes on ipc(2)
333 msgget(2) 2.0 See notes on ipc(2)
334 msgrcv(2) 2.0 See notes on ipc(2)
335 msgsnd(2) 2.0 See notes on ipc(2)
336 msync(2) 2.0
337 munlock(2) 2.0
338 munlockall(2) 2.0
339 munmap(2) 1.0
340 name_to_handle_at(2) 2.6.39
341 nanosleep(2) 2.0
342 newfstatat(2) 2.6.16 See stat(2)
343 nfsservctl(2) 2.2 Removed in 3.1
344 nice(2) 1.0
345 old_adjtimex(2) 2.0 Alpha only; see NOTES
346 old_getrlimit(2) 2.4 Old variant of getrlimit(2)
347 that used a different value
348 for RLIM_INFINITY
349 oldfstat(2) 1.0
350 oldlstat(2) 1.0
351 oldolduname(2) 1.0
352 oldstat(2) 1.0
353 oldumount(2) 2.4.116 Name of the old umount(2)
354 syscall on Alpha
355 olduname(2) 1.0
356 open(2) 1.0
357 open_by_handle_at(2) 2.6.39
358 openat(2) 2.6.16
359 or1k_atomic(2) 3.1 OpenRISC 1000 only
360 pause(2) 1.0
361 pciconfig_iobase(2) 2.2.15; 2.4 Not on x86
362 pciconfig_read(2) 2.0.26; 2.2 Not on x86
363 pciconfig_write(2) 2.0.26; 2.2 Not on x86
364 perf_event_open(2) 2.6.31 Was perf_counter_open() in
365 2.6.31; renamed in 2.6.32
366 personality(2) 1.2
367 perfctr(2) 2.2 SPARC only; removed in 2.6.34
368 perfmonctl(2) 2.4 IA-64 only
369 pipe(2) 1.0
370 pipe2(2) 2.6.27
371 pivot_root(2) 2.4
372 pkey_alloc(2) 4.8
373 pkey_free(2) 4.8
374 pkey_mprotect(2) 4.8
375 poll(2) 2.0.36; 2.2
376 ppoll(2) 2.6.16
377 prctl(2) 2.2
378 pread(2) Used for pread64(2) on AVR32
379 (port removed in Linux 4.12)
380 and Blackfin (port removed
381 in Linux 4.17)
382 pread64(2) Added as "pread" in 2.2;
383 renamed "pread64" in 2.6
384 preadv(2) 2.6.30
385 preadv2(2) 4.6
386 prlimit64(2) 2.6.36
387 process_vm_readv(2) 3.2
388 process_vm_writev(2) 3.2
389 pselect6(2) 2.6.16
390 ptrace(2) 1.0
391 pwrite(2) Used for pwrite64(2) on AVR32
392 (port removed in Linux 4.12)
393 and Blackfin (port removed in
394 Linux 4.17)
395 pwrite64(2) Added as "pwrite" in 2.2;
398 renamed "pwrite64" in 2.6
399 pwritev(2) 2.6.30
400 pwritev2(2) 4.6
401 query_module(2) 2.2 Removed in 2.6
402 quotactl(2) 1.0
403 read(2) 1.0
404 readahead(2) 2.4.13
405 readdir(2) 1.0
406 readlink(2) 1.0
407 readlinkat(2) 2.6.16
408 readv(2) 2.0
409 reboot(2) 1.0
410 recv(2) 2.0 See notes on socketcall(2)
411 recvfrom(2) 2.0 See notes on socketcall(2)
412 recvmsg(2) 2.0 See notes on socketcall(2)
413 recvmmsg(2) 2.6.33
414 remap_file_pages(2) 2.6 Deprecated since 3.16
415 removexattr(2) 2.6; 2.4.18
416 rename(2) 1.0
417 renameat(2) 2.6.16
418 renameat2(2) 3.15
419 request_key(2) 2.6.10
420 restart_syscall(2) 2.6
421 riscv_flush_icache(2) 4.15 RISC-V only
422 rmdir(2) 1.0
423 rseq(2) 4.18
424 rt_sigaction(2) 2.2
425 rt_sigpending(2) 2.2
426 rt_sigprocmask(2) 2.2
427 rt_sigqueueinfo(2) 2.2
428 rt_sigreturn(2) 2.2
429 rt_sigsuspend(2) 2.2
430 rt_sigtimedwait(2) 2.2
431 rt_tgsigqueueinfo(2) 2.6.31
432 rtas(2) 2.6.2 PowerPC/PowerPC64 only
433 s390_runtime_instr(2) 3.7 s390 only
434 s390_pci_mmio_read(2) 3.19 s390 only
435 s390_pci_mmio_write(2) 3.19 s390 only
436 s390_sthyi(2) 4.15 s390 only
437 s390_guarded_storage(2) 4.12 s390 only
438 sched_get_affinity(2) 2.6 Name of sched_getaffinity(2)
439 on SPARC and SPARC64
440 sched_get_priority_max(2) 2.0
441 sched_get_priority_min(2) 2.0
442 sched_getaffinity(2) 2.6
443 sched_getattr(2) 3.14
444 sched_getparam(2) 2.0
445 sched_getscheduler(2) 2.0
446 sched_rr_get_interval(2) 2.0
447 sched_set_affinity(2) 2.6 Name of sched_setaffinity(2)
448 on SPARC and SPARC64
449 sched_setaffinity(2) 2.6
450 sched_setattr(2) 3.14
451 sched_setparam(2) 2.0
452 sched_setscheduler(2) 2.0
453 sched_yield(2) 2.0
454 seccomp(2) 3.17
455 select(2) 1.0
456 semctl(2) 2.0 See notes on ipc(2)
457 semget(2) 2.0 See notes on ipc(2)
458 semop(2) 2.0 See notes on ipc(2)
459 semtimedop(2) 2.6; 2.4.22
460 send(2) 2.0 See notes on socketcall(2)
461 sendfile(2) 2.2
462 sendfile64(2) 2.6; 2.4.19
464 sendmmsg(2) 3.0
465 sendmsg(2) 2.0 See notes on socketcall(2)
466 sendto(2) 2.0 See notes on socketcall(2)
467 set_mempolicy(2) 2.6.6
468 set_robust_list(2) 2.6.17
469 set_thread_area(2) 2.6
470 set_tid_address(2) 2.6
471 set_tls(2) 2.6.11 ARM OABI/EABI only (constant
472 has __ARM_NR prefix)
473 setdomainname(2) 1.0
474 setfsgid(2) 1.2
475 setfsgid32(2) 2.4
476 setfsuid(2) 1.2
477 setfsuid32(2) 2.4
478 setgid(2) 1.0
479 setgid32(2) 2.4
480 setgroups(2) 1.0
481 setgroups32(2) 2.4
482 sethae(2) 2.0 Alpha only; see NOTES
483 sethostname(2) 1.0
484 setitimer(2) 1.0
485 setns(2) 3.0
486 setpgid(2) 1.0
487 setpgrp(2) 2.0 Alternative name for
488 setpgid(2) on Alpha
489 setpriority(2) 1.0
490 setregid(2) 1.0
491 setregid32(2) 2.4
492 setresgid(2) 2.2
493 setresgid32(2) 2.4
494 setresuid(2) 2.2
495 setresuid32(2) 2.4
496 setreuid(2) 1.0
497 setreuid32(2) 2.4
498 setrlimit(2) 1.0
499 setsid(2) 1.0
500 setsockopt(2) 2.0 See notes on socketcall(2)
501 settimeofday(2) 1.0
502 setuid(2) 1.0
503 setuid32(2) 2.4
504 setup(2) 1.0 Removed in 2.2
505 setxattr(2) 2.6; 2.4.18
506 sgetmask(2) 1.0
507 shmat(2) 2.0 See notes on ipc(2)
508 shmctl(2) 2.0 See notes on ipc(2)
509 shmdt(2) 2.0 See notes on ipc(2)
510 shmget(2) 2.0 See notes on ipc(2)
511 shutdown(2) 2.0 See notes on socketcall(2)
512 sigaction(2) 1.0
513 sigaltstack(2) 2.2
514 signal(2) 1.0
515 signalfd(2) 2.6.22
516 signalfd4(2) 2.6.27
517 sigpending(2) 1.0
518 sigprocmask(2) 1.0
519 sigreturn(2) 1.0
520 sigsuspend(2) 1.0
521 socket(2) 2.0 See notes on socketcall(2)
522 socketcall(2) 1.0
523 socketpair(2) 2.0 See notes on socketcall(2)
524 spill(2) 2.6.13 Xtensa only
525 splice(2) 2.6.17
526 spu_create(2) 2.6.16 PowerPC/PowerPC64 only
527 spu_run(2) 2.6.16 PowerPC/PowerPC64 only
528 sram_alloc(2) 2.6.22 Blackfin (port removed
530 in Linux 4.17)
531 sram_free(2) 2.6.22 Blackfin (port removed
532 in Linux 4.17)
533 ssetmask(2) 1.0
534 stat(2) 1.0
535 stat64(2) 2.4
536 statfs(2) 1.0
537 statfs64(2) 2.6
538 statx(2) 4.11
539 stime(2) 1.0
540 subpage_prot(2) 2.6.25 PowerPC/PowerPC64 only
541 swapcontext(2) 2.6.3 PowerPC/PowerPC64 only
542 switch_endian(2) 4.1 PowerPC64 only
543 swapcontext(2) 2.6.3 PowerPC only
544 swapoff(2) 1.0
545 swapon(2) 1.0
546 symlink(2) 1.0
547 symlinkat(2) 2.6.16
548 sync(2) 1.0
549 sync_file_range(2) 2.6.17
550 sync_file_range2(2) 2.6.22
551 syncfs(2) 2.6.39
552 sys_debug_setcontext(2) 2.6.11 PowerPC only
553 syscall(2) 1.0 Still available on ARM OABI
554 and MIPS O32 ABI
555 sysfs(2) 1.2
556 sysinfo(2) 1.0
557 syslog(2) 1.0
558 sysmips(2) 2.6.0 MIPS only
559 tee(2) 2.6.17
560 tgkill(2) 2.6
561 time(2) 1.0
562 timer_create(2) 2.6
563 timer_delete(2) 2.6
564 timer_getoverrun(2) 2.6
565 timer_gettime(2) 2.6
566 timer_settime(2) 2.6
567 timerfd_create(2) 2.6.25
568 timerfd_gettime(2) 2.6.25
569 timerfd_settime(2) 2.6.25
570 times(2) 1.0
571 tkill(2) 2.6; 2.4.22
572 truncate(2) 1.0
573 truncate64(2) 2.4
574 ugetrlimit(2) 2.4
575 umask(2) 1.0
576 umount(2) 1.0
577 umount2(2) 2.2
578 uname(2) 1.0
579 unlink(2) 1.0
580 unlinkat(2) 2.6.16
581 unshare(2) 2.6.16
582 uselib(2) 1.0
583 ustat(2) 1.0
584 userfaultfd(2) 4.3
585 usr26(2) 2.4.8.1 ARM OABI only
586 usr32(2) 2.4.8.1 ARM OABI only
587 utime(2) 1.0
588 utimensat(2) 2.6.22
589 utimes(2) 2.2
590 utrap_install(2) 2.2 SPARC64 only
591 vfork(2) 2.2
592 vhangup(2) 1.0
593 vm86old(2) 1.0 Was "vm86"; renamed in
596 2.0.28/2.2
597 vm86(2) 2.0.28; 2.2
598 vmsplice(2) 2.6.17
599 wait4(2) 1.0
600 waitid(2) 2.6.10
601 waitpid(2) 1.0
602 write(2) 1.0
603 writev(2) 2.0
604 xtensa(2) 2.6.13 Xtensa only
605 On many platforms, including x86-32, socket calls are all multiplexed
607 (via glibc wrapper functions) through socketcall(2) and similarly Sys‐
608 tem V IPC calls are multiplexed through ipc(2).
609 Although slots are reserved for them in the system call table, the fol‐
611 lowing system calls are not implemented in the standard kernel:
612 afs_syscall(2), break(2), ftime(2), getpmsg(2), gtty(2), idle(2),
613 lock(2), madvise1(2), mpx(2), phys(2), prof(2), profil(2), putpmsg(2),
614 security(2), stty(2), tuxcall(2), ulimit(2), and vserver(2) (see also
615 unimplemented(2)). However, ftime(3), profil(3), and ulimit(3) exist
616 as library routines. The slot for phys(2) is in use since kernel
617 2.1.116 for umount(2); phys(2) will never be implemented. The
618 getpmsg(2) and putpmsg(2) calls are for kernels patched to support
619 STREAMS, and may never be in the standard kernel.
620 There was briefly set_zone_reclaim(2), added in Linux 2.6.13, and
622 removed in 2.6.16; this system call was never available to user space.
623
625 Roughly speaking, the code belonging to the system call with number
626 __NR_xxx defined in /usr/include/asm/unistd.h can be found in the Linux
627 kernel source in the routine sys_xxx(). There are many exceptions,
628 however, mostly because older system calls were superseded by newer
629 ones, and this has been treated somewhat unsystematically. On plat‐
630 forms with proprietary operating-system emulation, such as sparc,
631 sparc64, and alpha, there are many additional system calls; mips64 also
632 contains a full set of 32-bit system calls.
633 Over time, changes to the interfaces of some system calls have been
635 necessary. One reason for such changes was the need to increase the
636 size of structures or scalar values passed to the system call. Because
637 of these changes, certain architectures (notably, longstanding 32-bit
638 architectures such as i386) now have various groups of related system
639 calls (e.g., truncate(2) and truncate64(2)) which perform similar
640 tasks, but which vary in details such as the size of their arguments.
641 (As noted earlier, applications are generally unaware of this: the
642 glibc wrapper functions do some work to ensure that the right system
643 call is invoked, and that ABI compatibility is preserved for old bina‐
644 ries.) Examples of systems calls that exist in multiple versions are
645 the following:
646 * By now there are three different versions of stat(2): sys_stat()
648 (slot __NR_oldstat), sys_newstat() (slot __NR_stat), and
649 sys_stat64() (slot __NR_stat64), with the last being the most cur‐
650 rent. A similar story applies for lstat(2) and fstat(2).
651 * Similarly, the defines __NR_oldolduname, __NR_olduname, and
653 __NR_uname refer to the routines sys_olduname(), sys_uname() and
654 sys_newuname().
655 * In Linux 2.0, a new version of vm86(2) appeared, with the old and
657 the new kernel routines being named sys_vm86old() and sys_vm86().
658 * In Linux 2.4, a new version of getrlimit(2) appeared, with the old
660 and the new kernel routines being named sys_old_getrlimit() (slot
661 __NR_getrlimit) and sys_getrlimit() (slot __NR_ugetrlimit).
662 * Linux 2.4 increased the size of user and group IDs from 16 to 32
664 bits. To support this change, a range of system calls were added
665 (e.g., chown32(2), getuid32(2), getgroups32(2), setresuid32(2)),
666 superseding earlier calls of the same name without the "32" suffix.
667 * Linux 2.4 added support for applications on 32-bit architectures to
669 access large files (i.e., files for which the sizes and file offsets
670 can't be represented in 32 bits.) To support this change, replace‐
671 ments were required for system calls that deal with file offsets and
672 sizes. Thus the following system calls were added: fcntl64(2), get‐
673 dents64(2), stat64(2), statfs64(2), truncate64(2), and their analogs
674 that work with file descriptors or symbolic links. These system
675 calls supersede the older system calls which, except in the case of
676 the "stat" calls, have the same name without the "64" suffix.
677 On newer platforms that only have 64-bit file access and 32-bit
679 UIDs/GIDs (e.g., alpha, ia64, s390x, x86-64), there is just a single
680 version of the UID/GID and file access system calls. On platforms
681 (typically, 32-bit platforms) where the *64 and *32 calls exist, the
682 other versions are obsolete.
683 * The rt_sig* calls were added in kernel 2.2 to support the addition
685 of real-time signals (see signal(7)). These system calls supersede
686 the older system calls of the same name without the "rt_" prefix.
687 * The select(2) and mmap(2) system calls use five or more arguments,
689 which caused problems in the way argument passing on the i386 used
690 to be set up. Thus, while other architectures have sys_select() and
691 sys_mmap() corresponding to __NR_select and __NR_mmap, on i386 one
692 finds old_select() and old_mmap() (routines that use a pointer to an
693 argument block) instead. These days passing five arguments is not a
694 problem any more, and there is a __NR__newselect that corresponds
695 directly to sys_select() and similarly __NR_mmap2. s390x is the
696 only 64-bit architecture that has old_mmap().
697 Architecture-specific details: Alpha
699 * getxgid(2) returns a pair of GID and effective GID via registers r0
700 and r20; it is provided instead of getgid(2) and getegid(2).
701 * getxpid(2) returns a pair of PID and parent PID via registers r0 and
703 r20; it is provided instead of getpid(2) and getppid(2).
704 * old_adjtimex(2) is a variant of adjtimex(2) that uses struct
706 timeval32, for compatibility with OSF/1.
707 * getxuid(2) returns a pair of GID and effective GID via registers r0
709 and r20; it is provided instead of getuid(2) and geteuid(2).
710 * sethae(2) is used for configuring the Host Address Extension regis‐
712 ter on low-cost Alphas in order to access address space beyond first
713 27 bits.
714
716 intro(2), syscall(2), unimplemented(2), errno(3), libc(7), vdso(7)
717
719 This page is part of release 5.02 of the Linux man-pages project. A
720 description of the project, information about reporting bugs, and the
721 latest version of this page, can be found at
722 https://www.kernel.org/doc/man-pages/.
723Linux 2019-03-06 SYSCALLS(2)