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; and the 5.x kernel series, which followed on from
87 kernel 4.20.
88 * In some cases, a system call was added to a stable kernel series
90 after it branched from the previous stable kernel series, and then
91 backported into the earlier stable kernel series. For example some
92 system calls that appeared in 2.6.x were also backported into a
93 2.4.x release after 2.4.15. When this is so, the version where the
94 system call appeared in both of the major kernel series is listed.
95 The list of system calls that are available as at kernel 4.19 (or in a
97 few cases only on older kernels) is as follows:
98 System call Kernel Notes
100 ───────────────────────────────────────────────────────────────────────
101 _llseek(2) 1.2
103 _newselect(2) 2.0
104 _sysctl(2) 2.0
105 accept(2) 2.0 See notes on socketcall(2)
106 accept4(2) 2.6.28
107 access(2) 1.0
108 acct(2) 1.0
109 add_key(2) 2.6.10
110 adjtimex(2) 1.0
111 alarm(2) 1.0
112 alloc_hugepages(2) 2.5.36 Removed in 2.5.44
113 arc_gettls(2) 3.9 ARC only
114 arc_settls(2) 3.9 ARC only
115 arc_usr_cmpxchg(2) 4.9 ARC only
116 arch_prctl(2) 2.6 x86_64, x86 since 4.12
117 atomic_barrier(2) 2.6.34 m68k only
118 atomic_cmpxchg_32(2) 2.6.34 m68k only
119 bdflush(2) 1.2 Deprecated (does nothing)
120 since 2.6
121 bfin_spinlock(2) 2.6.22 Blackfin only (port removed
122 in Linux 4.17)
123 bind(2) 2.0 See notes on socketcall(2)
124 bpf(2) 3.18
125 brk(2) 1.0
126 breakpoint(2) 2.2 ARM OABI only, defined with
127 __ARM_NR prefix
128 cacheflush(2) 1.2 Not on x86
129 capget(2) 2.2
130 capset(2) 2.2
131 chdir(2) 1.0
132 chmod(2) 1.0
134 chown(2) 2.2 See chown(2) for
135 version details
136 chown32(2) 2.4
137 chroot(2) 1.0
138 clock_adjtime(2) 2.6.39
139 clock_getres(2) 2.6
140 clock_gettime(2) 2.6
141 clock_nanosleep(2) 2.6
142 clock_settime(2) 2.6
143 clone2(2) 2.4 IA-64 only
144 clone(2) 1.0
145 clone3(2) 5.3
146 close(2) 1.0
147 cmpxchg_badaddr(2) 2.6.36 Tile only (port removed
148 in Linux 4.17)
149 connect(2) 2.0 See notes on socketcall(2)
150 copy_file_range(2) 4.5
151 creat(2) 1.0
152 create_module(2) 1.0 Removed in 2.6
153 delete_module(2) 1.0
154 dma_memcpy(2) 2.6.22 Blackfin only (port removed
155 in Linux 4.17)
156 dup(2) 1.0
157 dup2(2) 1.0
158 dup3(2) 2.6.27
159 epoll_create(2) 2.6
160 epoll_create1(2) 2.6.27
161 epoll_ctl(2) 2.6
162 epoll_pwait(2) 2.6.19
163 epoll_wait(2) 2.6
164 eventfd(2) 2.6.22
165 eventfd2(2) 2.6.27
166 execv(2) 2.0 SPARC/SPARC64 only, for
167 compatibility with SunOS
168 execve(2) 1.0
169 execveat(2) 3.19
170 exit(2) 1.0
171 exit_group(2) 2.6
172 faccessat(2) 2.6.16
173 fadvise64(2) 2.6
174 fadvise64_64(2) 2.6
175 fallocate(2) 2.6.23
176 fanotify_init(2) 2.6.37
177 fanotify_mark(2) 2.6.37
178 fchdir(2) 1.0
179 fchmod(2) 1.0
180 fchmodat(2) 2.6.16
181 fchown(2) 1.0
182 fchown32(2) 2.4
183 fchownat(2) 2.6.16
184 fcntl(2) 1.0
185 fcntl64(2) 2.4
186 fdatasync(2) 2.0
187 fgetxattr(2) 2.6; 2.4.18
188 finit_module(2) 3.8
189 flistxattr(2) 2.6; 2.4.18
190 flock(2) 2.0
191 fork(2) 1.0
192 free_hugepages(2) 2.5.36 Removed in 2.5.44
193 fremovexattr(2) 2.6; 2.4.18
194 fsconfig(2) 5.2
195 fsetxattr(2) 2.6; 2.4.18
196 fsmount(2) 5.2
197 fsopen(2) 5.2
198 fspick(2) 5.2
200 fstat(2) 1.0
201 fstat64(2) 2.4
202 fstatat64(2) 2.6.16
203 fstatfs(2) 1.0
204 fstatfs64(2) 2.6
205 fsync(2) 1.0
206 ftruncate(2) 1.0
207 ftruncate64(2) 2.4
208 futex(2) 2.6
209 futimesat(2) 2.6.16
210 get_kernel_syms(2) 1.0 Removed in 2.6
211 get_mempolicy(2) 2.6.6
212 get_robust_list(2) 2.6.17
213 get_thread_area(2) 2.6
214 get_tls(2) 4.15 ARM OABI only, has
215 __ARM_NR prefix
216 getcpu(2) 2.6.19
217 getcwd(2) 2.2
218 getdents(2) 2.0
219 getdents64(2) 2.4
220 getdomainname(2) 2.2 SPARC, SPARC64; available
221 as osf_getdomainname(2)
222 on Alpha since Linux 2.0
223 getdtablesize(2) 2.0 SPARC (removed in 2.6.26),
224 available on Alpha as
225 osf_getdtablesize(2)
226 getegid(2) 1.0
227 getegid32(2) 2.4
228 geteuid(2) 1.0
229 geteuid32(2) 2.4
230 getgid(2) 1.0
231 getgid32(2) 2.4
232 getgroups(2) 1.0
233 getgroups32(2) 2.4
234 gethostname(2) 2.0 Alpha, was available on
235 SPARC up to Linux 2.6.26
236 getitimer(2) 1.0
237 getpeername(2) 2.0 See notes on socketcall(2)
238 getpagesize(2) 2.0 Not on x86
239 getpgid(2) 1.0
240 getpgrp(2) 1.0
241 getpid(2) 1.0
242 getppid(2) 1.0
243 getpriority(2) 1.0
244 getrandom(2) 3.17
245 getresgid(2) 2.2
246 getresgid32(2) 2.4
247 getresuid(2) 2.2
248 getresuid32(2) 2.4
249 getrlimit(2) 1.0
250 getrusage(2) 1.0
251 getsid(2) 2.0
252 getsockname(2) 2.0 See notes on socketcall(2)
253 getsockopt(2) 2.0 See notes on socketcall(2)
254 gettid(2) 2.4.11
255 gettimeofday(2) 1.0
256 getuid(2) 1.0
257 getuid32(2) 2.4
258 getunwind(2) 2.4.8 IA-64 only; deprecated
259 getxattr(2) 2.6; 2.4.18
260 getxgid(2) 2.0 Alpha only; see NOTES
261 getxpid(2) 2.0 Alpha only; see NOTES
262 getxuid(2) 2.0 Alpha only; see NOTES
263 init_module(2) 1.0
264 inotify_add_watch(2) 2.6.13
266 inotify_init(2) 2.6.13
267 inotify_init1(2) 2.6.27
268 inotify_rm_watch(2) 2.6.13
269 io_cancel(2) 2.6
270 io_destroy(2) 2.6
271 io_getevents(2) 2.6
272 io_pgetevents(2) 4.18
273 io_setup(2) 2.6
274 io_submit(2) 2.6
275 io_uring_enter(2) 5.1
276 io_uring_register(2) 5.1
277 io_uring_setup(2) 5.1
278 ioctl(2) 1.0
279 ioperm(2) 1.0
280 iopl(2) 1.0
281 ioprio_get(2) 2.6.13
282 ioprio_set(2) 2.6.13
283 ipc(2) 1.0
284 kcmp(2) 3.5
285 kern_features(2) 3.7 SPARC64 only
286 kexec_file_load(2) 3.17
287 kexec_load(2) 2.6.13
288 keyctl(2) 2.6.10
289 kill(2) 1.0
290 lchown(2) 1.0 See chown(2) for
291 version details
292 lchown32(2) 2.4
293 lgetxattr(2) 2.6; 2.4.18
294 link(2) 1.0
295 linkat(2) 2.6.16
296 listen(2) 2.0 See notes on socketcall(2)
297 listxattr(2) 2.6; 2.4.18
298 llistxattr(2) 2.6; 2.4.18
299 lookup_dcookie(2) 2.6
300 lremovexattr(2) 2.6; 2.4.18
301 lseek(2) 1.0
302 lsetxattr(2) 2.6; 2.4.18
303 lstat(2) 1.0
304 lstat64(2) 2.4
305 madvise(2) 2.4
306 mbind(2) 2.6.6
307 memory_ordering(2) 2.2 SPARC64 only
308 metag_get_tls(2) 3.9 Metag only (port removed
309 in Linux 4.17)
310 metag_set_fpu_flags(2) 3.9 Metag only (port removed
311 in Linux 4.17)
312 metag_set_tls(2) 3.9 Metag only (port removed
313 in Linux 4.17)
314 metag_setglobalbit(2) 3.9 Metag only (port removed
315 in Linux 4.17)
316 membarrier(2) 3.17
317 memfd_create(2) 3.17
318 migrate_pages(2) 2.6.16
319 mincore(2) 2.4
320 mkdir(2) 1.0
321 mkdirat(2) 2.6.16
322 mknod(2) 1.0
323 mknodat(2) 2.6.16
324 mlock(2) 2.0
325 mlock2(2) 4.4
326 mlockall(2) 2.0
327 mmap(2) 1.0
328 mmap2(2) 2.4
329 modify_ldt(2) 1.0
330 mount(2) 1.0
332 move_mount(2) 5.2
333 move_pages(2) 2.6.18
334 mprotect(2) 1.0
335 mq_getsetattr(2) 2.6.6
336 mq_notify(2) 2.6.6
337 mq_open(2) 2.6.6
338 mq_timedreceive(2) 2.6.6
339 mq_timedsend(2) 2.6.6
340 mq_unlink(2) 2.6.6
341 mremap(2) 2.0
342 msgctl(2) 2.0 See notes on ipc(2)
343 msgget(2) 2.0 See notes on ipc(2)
344 msgrcv(2) 2.0 See notes on ipc(2)
345 msgsnd(2) 2.0 See notes on ipc(2)
346 msync(2) 2.0
347 munlock(2) 2.0
348 munlockall(2) 2.0
349 munmap(2) 1.0
350 name_to_handle_at(2) 2.6.39
351 nanosleep(2) 2.0
352 newfstatat(2) 2.6.16 See stat(2)
353 nfsservctl(2) 2.2 Removed in 3.1
354 nice(2) 1.0
355 old_adjtimex(2) 2.0 Alpha only; see NOTES
356 old_getrlimit(2) 2.4 Old variant of getrlimit(2)
357 that used a different value
358 for RLIM_INFINITY
359 oldfstat(2) 1.0
360 oldlstat(2) 1.0
361 oldolduname(2) 1.0
362 oldstat(2) 1.0
363 oldumount(2) 2.4.116 Name of the old umount(2)
364 syscall on Alpha
365 olduname(2) 1.0
366 open(2) 1.0
367 open_by_handle_at(2) 2.6.39
368 open_tree(2) 5.2
369 openat(2) 2.6.16
370 openat2(2) 5.6
371 or1k_atomic(2) 3.1 OpenRISC 1000 only
372 pause(2) 1.0
373 pciconfig_iobase(2) 2.2.15; 2.4 Not on x86
374 pciconfig_read(2) 2.0.26; 2.2 Not on x86
375 pciconfig_write(2) 2.0.26; 2.2 Not on x86
376 perf_event_open(2) 2.6.31 Was perf_counter_open() in
377 2.6.31; renamed in 2.6.32
378 personality(2) 1.2
379 perfctr(2) 2.2 SPARC only; removed in 2.6.34
380 perfmonctl(2) 2.4 IA-64 only
381 pidfd_getfd(2) 5.6
382 pidfd_send_signal(2) 5.1
383 pidfd_open(2) 5.3
384 pipe(2) 1.0
385 pipe2(2) 2.6.27
386 pivot_root(2) 2.4
387 pkey_alloc(2) 4.8
388 pkey_free(2) 4.8
389 pkey_mprotect(2) 4.8
390 poll(2) 2.0.36; 2.2
391 ppoll(2) 2.6.16
392 prctl(2) 2.2
393 pread(2) Used for pread64(2) on AVR32
398 (port removed in Linux 4.12)
399 and Blackfin (port removed
400 in Linux 4.17)
401 pread64(2) Added as "pread" in 2.2;
402 renamed "pread64" in 2.6
403 preadv(2) 2.6.30
404 preadv2(2) 4.6
405 prlimit64(2) 2.6.36
406 process_vm_readv(2) 3.2
407 process_vm_writev(2) 3.2
408 pselect6(2) 2.6.16
409 ptrace(2) 1.0
410 pwrite(2) Used for pwrite64(2)
411 on AVR32 (port removed
412 in Linux 4.12) and Blackfin
413 (port removed in Linux 4.17)
414 pwrite64(2) Added as "pwrite" in 2.2;
415 renamed "pwrite64" in 2.6
416 pwritev(2) 2.6.30
417 pwritev2(2) 4.6
418 query_module(2) 2.2 Removed in 2.6
419 quotactl(2) 1.0
420 read(2) 1.0
421 readahead(2) 2.4.13
422 readdir(2) 1.0
423 readlink(2) 1.0
424 readlinkat(2) 2.6.16
425 readv(2) 2.0
426 reboot(2) 1.0
427 recv(2) 2.0 See notes on socketcall(2)
428 recvfrom(2) 2.0 See notes on socketcall(2)
429 recvmsg(2) 2.0 See notes on socketcall(2)
430 recvmmsg(2) 2.6.33
431 remap_file_pages(2) 2.6 Deprecated since 3.16
432 removexattr(2) 2.6; 2.4.18
433 rename(2) 1.0
434 renameat(2) 2.6.16
435 renameat2(2) 3.15
436 request_key(2) 2.6.10
437 restart_syscall(2) 2.6
438 riscv_flush_icache(2) 4.15 RISC-V only
439 rmdir(2) 1.0
440 rseq(2) 4.18
441 rt_sigaction(2) 2.2
442 rt_sigpending(2) 2.2
443 rt_sigprocmask(2) 2.2
444 rt_sigqueueinfo(2) 2.2
445 rt_sigreturn(2) 2.2
446 rt_sigsuspend(2) 2.2
447 rt_sigtimedwait(2) 2.2
448 rt_tgsigqueueinfo(2) 2.6.31
449 rtas(2) 2.6.2 PowerPC/PowerPC64 only
450 s390_runtime_instr(2) 3.7 s390 only
451 s390_pci_mmio_read(2) 3.19 s390 only
452 s390_pci_mmio_write(2) 3.19 s390 only
453 s390_sthyi(2) 4.15 s390 only
454 s390_guarded_storage(2) 4.12 s390 only
455 sched_get_affinity(2) 2.6 Name of sched_getaffinity(2)
456 on SPARC and SPARC64
457 sched_get_priority_max(2) 2.0
458 sched_get_priority_min(2) 2.0
459 sched_getaffinity(2) 2.6
460 sched_getattr(2) 3.14
461 sched_getparam(2) 2.0
462 sched_getscheduler(2) 2.0
464 sched_rr_get_interval(2) 2.0
465 sched_set_affinity(2) 2.6 Name of sched_setaffinity(2)
466 on SPARC and SPARC64
467 sched_setaffinity(2) 2.6
468 sched_setattr(2) 3.14
469 sched_setparam(2) 2.0
470 sched_setscheduler(2) 2.0
471 sched_yield(2) 2.0
472 seccomp(2) 3.17
473 select(2) 1.0
474 semctl(2) 2.0 See notes on ipc(2)
475 semget(2) 2.0 See notes on ipc(2)
476 semop(2) 2.0 See notes on ipc(2)
477 semtimedop(2) 2.6; 2.4.22
478 send(2) 2.0 See notes on socketcall(2)
479 sendfile(2) 2.2
480 sendfile64(2) 2.6; 2.4.19
481 sendmmsg(2) 3.0
482 sendmsg(2) 2.0 See notes on socketcall(2)
483 sendto(2) 2.0 See notes on socketcall(2)
484 set_mempolicy(2) 2.6.6
485 set_robust_list(2) 2.6.17
486 set_thread_area(2) 2.6
487 set_tid_address(2) 2.6
488 set_tls(2) 2.6.11 ARM OABI/EABI only (constant
489 has __ARM_NR prefix)
490 setdomainname(2) 1.0
491 setfsgid(2) 1.2
492 setfsgid32(2) 2.4
493 setfsuid(2) 1.2
494 setfsuid32(2) 2.4
495 setgid(2) 1.0
496 setgid32(2) 2.4
497 setgroups(2) 1.0
498 setgroups32(2) 2.4
499 sethae(2) 2.0 Alpha only; see NOTES
500 sethostname(2) 1.0
501 setitimer(2) 1.0
502 setns(2) 3.0
503 setpgid(2) 1.0
504 setpgrp(2) 2.0 Alternative name for
505 setpgid(2) on Alpha
506 setpriority(2) 1.0
507 setregid(2) 1.0
508 setregid32(2) 2.4
509 setresgid(2) 2.2
510 setresgid32(2) 2.4
511 setresuid(2) 2.2
512 setresuid32(2) 2.4
513 setreuid(2) 1.0
514 setreuid32(2) 2.4
515 setrlimit(2) 1.0
516 setsid(2) 1.0
517 setsockopt(2) 2.0 See notes on socketcall(2)
518 settimeofday(2) 1.0
519 setuid(2) 1.0
520 setuid32(2) 2.4
521 setup(2) 1.0 Removed in 2.2
522 setxattr(2) 2.6; 2.4.18
523 sgetmask(2) 1.0
524 shmat(2) 2.0 See notes on ipc(2)
525 shmctl(2) 2.0 See notes on ipc(2)
526 shmdt(2) 2.0 See notes on ipc(2)
527 shmget(2) 2.0 See notes on ipc(2)
528 shutdown(2) 2.0 See notes on socketcall(2)
530 sigaction(2) 1.0
531 sigaltstack(2) 2.2
532 signal(2) 1.0
533 signalfd(2) 2.6.22
534 signalfd4(2) 2.6.27
535 sigpending(2) 1.0
536 sigprocmask(2) 1.0
537 sigreturn(2) 1.0
538 sigsuspend(2) 1.0
539 socket(2) 2.0 See notes on socketcall(2)
540 socketcall(2) 1.0
541 socketpair(2) 2.0 See notes on socketcall(2)
542 spill(2) 2.6.13 Xtensa only
543 splice(2) 2.6.17
544 spu_create(2) 2.6.16 PowerPC/PowerPC64 only
545 spu_run(2) 2.6.16 PowerPC/PowerPC64 only
546 sram_alloc(2) 2.6.22 Blackfin (port removed
547 in Linux 4.17)
548 sram_free(2) 2.6.22 Blackfin (port removed
549 in Linux 4.17)
550 ssetmask(2) 1.0
551 stat(2) 1.0
552 stat64(2) 2.4
553 statfs(2) 1.0
554 statfs64(2) 2.6
555 statx(2) 4.11
556 stime(2) 1.0
557 subpage_prot(2) 2.6.25 PowerPC/PowerPC64 only
558 swapcontext(2) 2.6.3 PowerPC/PowerPC64 only
559 switch_endian(2) 4.1 PowerPC64 only
560 swapcontext(2) 2.6.3 PowerPC only
561 swapoff(2) 1.0
562 swapon(2) 1.0
563 symlink(2) 1.0
564 symlinkat(2) 2.6.16
565 sync(2) 1.0
566 sync_file_range(2) 2.6.17
567 sync_file_range2(2) 2.6.22
568 syncfs(2) 2.6.39
569 sys_debug_setcontext(2) 2.6.11 PowerPC only
570 syscall(2) 1.0 Still available on ARM OABI
571 and MIPS O32 ABI
572 sysfs(2) 1.2
573 sysinfo(2) 1.0
574 syslog(2) 1.0
575 sysmips(2) 2.6.0 MIPS only
576 tee(2) 2.6.17
577 tgkill(2) 2.6
578 time(2) 1.0
579 timer_create(2) 2.6
580 timer_delete(2) 2.6
581 timer_getoverrun(2) 2.6
582 timer_gettime(2) 2.6
583 timer_settime(2) 2.6
584 timerfd_create(2) 2.6.25
585 timerfd_gettime(2) 2.6.25
586 timerfd_settime(2) 2.6.25
587 times(2) 1.0
588 tkill(2) 2.6; 2.4.22
589 truncate(2) 1.0
590 truncate64(2) 2.4
591 ugetrlimit(2) 2.4
592 umask(2) 1.0
593 umount(2) 1.0
594 umount2(2) 2.2
596 uname(2) 1.0
597 unlink(2) 1.0
598 unlinkat(2) 2.6.16
599 unshare(2) 2.6.16
600 uselib(2) 1.0
601 ustat(2) 1.0
602 userfaultfd(2) 4.3
603 usr26(2) 2.4.8.1 ARM OABI only
604 usr32(2) 2.4.8.1 ARM OABI only
605 utime(2) 1.0
606 utimensat(2) 2.6.22
607 utimes(2) 2.2
608 utrap_install(2) 2.2 SPARC64 only
609 vfork(2) 2.2
610 vhangup(2) 1.0
611 vm86old(2) 1.0 Was "vm86"; renamed in
612 2.0.28/2.2
613 vm86(2) 2.0.28; 2.2
614 vmsplice(2) 2.6.17
615 wait4(2) 1.0
616 waitid(2) 2.6.10
617 waitpid(2) 1.0
618 write(2) 1.0
619 writev(2) 2.0
620 xtensa(2) 2.6.13 Xtensa only
621 On many platforms, including x86-32, socket calls are all multiplexed
623 (via glibc wrapper functions) through socketcall(2) and similarly Sys‐
624 tem V IPC calls are multiplexed through ipc(2).
625 Although slots are reserved for them in the system call table, the fol‐
627 lowing system calls are not implemented in the standard kernel:
628 afs_syscall(2), break(2), ftime(2), getpmsg(2), gtty(2), idle(2),
629 lock(2), madvise1(2), mpx(2), phys(2), prof(2), profil(2), putpmsg(2),
630 security(2), stty(2), tuxcall(2), ulimit(2), and vserver(2) (see also
631 unimplemented(2)). However, ftime(3), profil(3), and ulimit(3) exist
632 as library routines. The slot for phys(2) is in use since kernel
633 2.1.116 for umount(2); phys(2) will never be implemented. The
634 getpmsg(2) and putpmsg(2) calls are for kernels patched to support
635 STREAMS, and may never be in the standard kernel.
636 There was briefly set_zone_reclaim(2), added in Linux 2.6.13, and
638 removed in 2.6.16; this system call was never available to user space.
639
641 Roughly speaking, the code belonging to the system call with number
642 __NR_xxx defined in /usr/include/asm/unistd.h can be found in the Linux
643 kernel source in the routine sys_xxx(). There are many exceptions,
644 however, mostly because older system calls were superseded by newer
645 ones, and this has been treated somewhat unsystematically. On plat‐
646 forms with proprietary operating-system emulation, such as sparc,
647 sparc64, and alpha, there are many additional system calls; mips64 also
648 contains a full set of 32-bit system calls.
649 Over time, changes to the interfaces of some system calls have been
651 necessary. One reason for such changes was the need to increase the
652 size of structures or scalar values passed to the system call. Because
653 of these changes, certain architectures (notably, longstanding 32-bit
654 architectures such as i386) now have various groups of related system
655 calls (e.g., truncate(2) and truncate64(2)) which perform similar
656 tasks, but which vary in details such as the size of their arguments.
657 (As noted earlier, applications are generally unaware of this: the
658 glibc wrapper functions do some work to ensure that the right system
659 call is invoked, and that ABI compatibility is preserved for old bina‐
660 ries.) Examples of systems calls that exist in multiple versions are
661 the following:
662 * By now there are three different versions of stat(2): sys_stat()
664 (slot __NR_oldstat), sys_newstat() (slot __NR_stat), and
665 sys_stat64() (slot __NR_stat64), with the last being the most cur‐
666 rent. A similar story applies for lstat(2) and fstat(2).
667 * Similarly, the defines __NR_oldolduname, __NR_olduname, and
669 __NR_uname refer to the routines sys_olduname(), sys_uname() and
670 sys_newuname().
671 * In Linux 2.0, a new version of vm86(2) appeared, with the old and
673 the new kernel routines being named sys_vm86old() and sys_vm86().
674 * In Linux 2.4, a new version of getrlimit(2) appeared, with the old
676 and the new kernel routines being named sys_old_getrlimit() (slot
677 __NR_getrlimit) and sys_getrlimit() (slot __NR_ugetrlimit).
678 * Linux 2.4 increased the size of user and group IDs from 16 to 32
680 bits. To support this change, a range of system calls were added
681 (e.g., chown32(2), getuid32(2), getgroups32(2), setresuid32(2)),
682 superseding earlier calls of the same name without the "32" suffix.
683 * Linux 2.4 added support for applications on 32-bit architectures to
685 access large files (i.e., files for which the sizes and file offsets
686 can't be represented in 32 bits.) To support this change, replace‐
687 ments were required for system calls that deal with file offsets and
688 sizes. Thus the following system calls were added: fcntl64(2), get‐
689 dents64(2), stat64(2), statfs64(2), truncate64(2), and their analogs
690 that work with file descriptors or symbolic links. These system
691 calls supersede the older system calls which, except in the case of
692 the "stat" calls, have the same name without the "64" suffix.
693 On newer platforms that only have 64-bit file access and 32-bit
695 UIDs/GIDs (e.g., alpha, ia64, s390x, x86-64), there is just a single
696 version of the UID/GID and file access system calls. On platforms
697 (typically, 32-bit platforms) where the *64 and *32 calls exist, the
698 other versions are obsolete.
699 * The rt_sig* calls were added in kernel 2.2 to support the addition
701 of real-time signals (see signal(7)). These system calls supersede
702 the older system calls of the same name without the "rt_" prefix.
703 * The select(2) and mmap(2) system calls use five or more arguments,
705 which caused problems in the way argument passing on the i386 used
706 to be set up. Thus, while other architectures have sys_select() and
707 sys_mmap() corresponding to __NR_select and __NR_mmap, on i386 one
708 finds old_select() and old_mmap() (routines that use a pointer to an
709 argument block) instead. These days passing five arguments is not a
710 problem any more, and there is a __NR__newselect that corresponds
711 directly to sys_select() and similarly __NR_mmap2. s390x is the
712 only 64-bit architecture that has old_mmap().
713 Architecture-specific details: Alpha
715 * getxgid(2) returns a pair of GID and effective GID via registers r0
716 and r20; it is provided instead of getgid(2) and getegid(2).
717 * getxpid(2) returns a pair of PID and parent PID via registers r0 and
719 r20; it is provided instead of getpid(2) and getppid(2).
720 * old_adjtimex(2) is a variant of adjtimex(2) that uses struct
722 timeval32, for compatibility with OSF/1.
723 * getxuid(2) returns a pair of GID and effective GID via registers r0
725 and r20; it is provided instead of getuid(2) and geteuid(2).
726 * sethae(2) is used for configuring the Host Address Extension regis‐
728 ter on low-cost Alphas in order to access address space beyond first
729 27 bits.
730
732 intro(2), syscall(2), unimplemented(2), errno(3), libc(7), vdso(7)
733
735 This page is part of release 5.07 of the Linux man-pages project. A
736 description of the project, information about reporting bugs, and the
737 latest version of this page, can be found at
738 https://www.kernel.org/doc/man-pages/.
739Linux 2020-04-11 SYSCALLS(2)