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SYSCALLS(2)		   Linux Programmer's Manual		   SYSCALLS(2)

NAME
       syscalls - Linux system calls

SYNOPSIS
       Linux system calls.

DESCRIPTION
       The system call is the fundamental interface between an application and
       the Linux kernel.

   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  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
       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  sys‐
       tem  call,  and	then setting errno appropriately after the system call
       has returned.   (These  are  the	 same  steps  that  are	 performed  by
       syscall(2), which can be used to invoke system calls for which no wrap‐
       per 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	 posi‐
       tive), copies it to 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,	truncate(2)  and trun‐
       cate64(2), and the glibc truncate() wrapper function  checks  which  of
       those  system  calls  are  provided  by the kernel and determines which
       should be employed.

   System call list
       Below is a list of those system calls that are  common  to  most	 plat‐
       forms.  In the list, the 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:

       *  Where	 no  kernel  version is indicated, the system call appeared in
	  kernel 1.0 or earlier.

       *  Where a system call is marked "1.2" this means the system call prob‐
	  ably	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	initi‐
	  ated	from  a	 branch	 of kernel 1.0.6 via the 1.1.x unstable kernel
	  series.)

       *  Where a system call is marked "2.0" this means the system call prob‐
	  ably	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	initi‐
	  ated from a branch of kernel 1.2.x, somewhere around 1.2.10, via the
	  1.3.x unstable kernel series.)

       *  Where a system call is marked "2.2" this means the system call prob‐
	  ably	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 initi‐
	  ated	from  a	 branch of kernel 2.0.21 via the 2.1.x unstable kernel
	  series.)

       *  Where a system call is marked "2.4" this means the system call prob‐
	  ably	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 initi‐
	  ated	from  a	 branch	 of kernel 2.2.8 via the 2.3.x unstable kernel
	  series.)

       *  Where a system call is marked "2.6" this means the system call prob‐
	  ably	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.)

       *  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.

       *  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.

       The  list of system calls that are available as at kernel 2.6.28 (or in
       a few cases only on older kernels) is as follows:

       System call		   Kernel	 Notes
       ───────────────────────────────────────────────────────────────────────

       _llseek(2)		   1.2
       _newselect(2)
       _sysctl(2)
       accept(2)
       accept4(2)		   2.6.28
       access(2)
       acct(2)
       add_key(2)		   2.6.11
       adjtimex(2)
       afs_syscall(2)				 Not implemented
       alarm(2)
       alloc_hugepages(2)	   2.5.36	 Removed in 2.5.44
       bdflush(2)				 Deprecated  (does   nothing)
						 since 2.6
       bind(2)
       break(2)					 Not implemented
       brk(2)
       cacheflush(2)		   1.2		 Not on i386
       capget(2)		   2.2
       capset(2)		   2.2
       chdir(2)
       chmod(2)
       chown(2)
       chown32(2)		   2.4
       chroot(2)
       clock_getres(2)		   2.6
       clock_gettime(2)		   2.6
       clock_nanosleep(2)	   2.6
       clock_settime(2)		   2.6
       clone(2)
       close(2)
       connect(2)
       creat(2)
       create_module(2)
       delete_module(2)
       dup(2)

       dup2(2)
       dup3(2)			   2.6.27
       epoll_create(2)		   2.6
       epoll_create1(2)		   2.6.27
       epoll_ctl(2)		   2.6
       epoll_pwait(2)		   2.6.19
       epoll_wait(2)		   2.6
       eventfd(2)		   2.6.22
       eventfd2(2)		   2.6.27
       execve(2)
       exit(2)
       exit_group(2)		   2.6
       faccessat(2)		   2.6.16
       fadvise64(2)		   2.6
       fadvise64_64(2)		   2.6
       fallocate(2)		   2.6.23
       fchdir(2)
       fchmod(2)
       fchmodat(2)		   2.6.16
       fchown(2)
       fchown32(2)		   2.4
       fchownat(2)		   2.6.16
       fcntl(2)
       fcntl64(2)		   2.4
       fdatasync(2)
       fgetxattr(2)		   2.6; 2.4.18
       flistxattr(2)		   2.6; 2.4.18
       flock(2)			   2.0
       fork(2)
       free_hugepages(2)	   2.5.36	 Removed in 2.5.44
       fremovexattr(2)		   2.6; 2.4.18
       fsetxattr(2)		   2.6; 2.4.18
       fstat(2)
       fstat64(2)		   2.4
       fstatat64(2)		   2.6.16
       fstatfs(2)
       fstatfs64(2)		   2.6
       fsync(2)
       ftime(2)					 Not implemented
       ftruncate(2)
       ftruncate64(2)		   2.4
       futex(2)			   2.6
       futimesat(2)		   2.6.16
       get_kernel_syms(2)
       get_mempolicy(2)		   2.6.6
       get_robust_list(2)	   2.6.17
       get_thread_area(2)	   2.6
       getcpu(2)		   2.6.19
       getcwd(2)		   2.2
       getdents(2)		   2.0
       getdents64(2)		   2.4
       getegid(2)
       getegid32(2)		   2.4
       geteuid(2)
       geteuid32(2)		   2.4
       getgid(2)
       getgid32(2)		   2.4
       getgroups(2)
       getgroups32(2)		   2.4
       getitimer(2)
       getpeername(2)
       getpagesize(2)		   2.0		 Not on i386
       getpgid(2)
       getpgrp(2)
       getpid(2)

       getpmsg(2)				 Not implemented
       getppid(2)
       getpriority(2)
       getresgid(2)		   2.2
       getresgid32(2)		   2.4
       getresuid(2)		   2.2
       getresuid32(2)		   2.4
       getrlimit(2)
       getrusage(2)
       getsid(2)		   2.0
       getsockname(2)
       getsockopt(2)
       gettid(2)		   2.4.11
       gettimeofday(2)
       getuid(2)
       getuid32(2)		   2.4
       getxattr(2)		   2.6; 2.4.18
       gtty(2)					 Not implemented
       idle(2)					 Not implemented
       init_module(2)
       inotify_add_watch(2)	   2.6.13
       inotify_init(2)		   2.6.13
       inotify_init1(2)		   2.6.27
       inotify_rm_watch(2)	   2.6.13
       io_cancel(2)		   2.6
       io_destroy(2)		   2.6
       io_getevents(2)		   2.6
       io_setup(2)		   2.6
       io_submit(2)		   2.6
       ioctl(2)
       ioperm(2)
       iopl(2)
       ioprio_get(2)		   2.6.13
       ioprio_set(2)		   2.6.13
       ipc(2)
       kexec_load(2)		   2.6.7
       keyctl(2)		   2.6.11
       kill(2)
       lchown(2)		   2.2
       lchown32(2)		   2.4
       lgetxattr(2)		   2.6; 2.4.18
       link(2)
       linkat(2)		   2.6.16
       listen(2)
       listxattr(2)		   2.6; 2.4.18
       llistxattr(2)		   2.6; 2.4.18
       lock(2)					 Not implemented
       lookup_dcookie(2)	   2.6
       lremovexattr(2)		   2.6; 2.4.18
       lseek(2)
       lsetxattr(2)		   2.6; 2.4.18
       lstat(2)
       lstat64(2)		   2.4
       madvise(2)		   2.4
       madvise1(2)		   2.4
       mbind(2)			   2.6.6
       migrate_pages(2)		   2.6.16
       mincore(2)		   2.4
       mkdir(2)
       mkdirat(2)		   2.6.16
       mknod(2)
       mknodat(2)		   2.6.16
       mlock(2)
       mlockall(2)
       mmap(2)

       mmap2(2)			   2.4
       modify_ldt(2)
       mount(2)
       move_pages(2)		   2.6.18
       mprotect(2)
       mpx(2)					 Not implemented
       mq_getsetattr(2)		   2.6.6
       mq_notify(2)		   2.6.6
       mq_open(2)		   2.6.6
       mq_timedreceive(2)	   2.6.6
       mq_timedsend(2)		   2.6.6
       mq_unlink(2)
       mremap(2)		   2.0
       msgctl(2)
       msgget(2)
       msgrcv(2)
       msgsnd(2)
       msync(2)			   2.0
       munlock(2)
       munlockall(2)
       munmap(2)
       nanosleep(2)		   2.0
       nfsservctl(2)		   2.2
       nice(2)
       oldfstat(2)
       oldlstat(2)
       oldolduname(2)
       oldstat(2)
       olduname(2)
       open(2)
       openat(2)		   2.6.16
       pause(2)
       pciconfig_iobase(2)	   2.2.15; 2.4	 Not on i386
       pciconfig_read(2)	   2.0.26; 2.2	 Not on i386
       pciconfig_write(2)	   2.0.26; 2.2	 Not on i386
       personality(2)		   1.2
       phys(2)					 Not implemented
       pipe(2)
       pipe2(2)			   2.6.27
       pivot_root(2)		   2.4
       poll(2)			   2.2
       ppoll(2)			   2.6.16
       prctl(2)			   2.2
       pread64(2)				 Added as "pread" in 2.2;
						 renamed "pread64" in 2.6
       preadv(2)		   2.6.30
       prof(2)					 Not implemented
       profil(2)				 Not implemented
       pselect6(2)		   2.6.16
       ptrace(2)
       putpmsg(2)				 Not implemented
       pwrite64(2)				 Added as "pwrite" in 2.2;
						 renamed "pwrite64" in 2.6
       pwritev(2)		   2.6.30
       query_module(2)		   2.2
       quotactl(2)
       read(2)
       readahead(2)		   2.4.13
       readdir(2)
       readlink(2)
       readlinkat(2)		   2.6.16
       readv(2)			   2.0
       reboot(2)
       recv(2)
       recvfrom(2)

       recvmsg(2)
       remap_file_pages(2)	   2.6
       removexattr(2)		   2.6; 2.4.18
       rename(2)
       renameat(2)		   2.6.16
       request_key(2)		   2.6.11
       restart_syscall(2)	   2.6
       rmdir(2)
       rt_sigaction(2)		   2.2
       rt_sigpending(2)		   2.2
       rt_sigprocmask(2)	   2.2
       rt_sigqueueinfo(2)	   2.2
       rt_sigreturn(2)		   2.2
       rt_sigsuspend(2)		   2.2
       rt_sigtimedwait(2)	   2.2
       sched_get_priority_max(2)   2.0
       sched_get_priority_min(2)   2.0
       sched_getaffinity(2)	   2.6
       sched_getparam(2)	   2.0
       sched_getscheduler(2)	   2.0
       sched_rr_get_interval(2)	   2.0
       sched_setaffinity(2)	   2.6
       sched_setparam(2)	   2.0
       sched_setscheduler(2)	   2.0
       sched_yield(2)		   2.0
       security(2)				 Not implemented
       select(2)
       semctl(2)
       semget(2)
       semop(2)
       semtimedop(2)		   2.6; 2.4.22
       send(2)
       sendfile(2)		   2.2
       sendfile64(2)		   2.6; 2.4.19
       sendmsg(2)
       sendto(2)
       set_mempolicy(2)		   2.6.6
       set_robust_list(2)	   2.6.17
       set_thread_area(2)	   2.6
       set_tid_address(2)	   2.6
       set_zone_reclaim(2)	   2.6.13	 Removed in 2.6.16 (was never
						 available to userspace)
       setdomainname(2)
       setfsgid(2)		   1.2
       setfsgid32(2)		   2.4
       setfsuid(2)		   1.2
       setfsuid32(2)		   2.4
       setgid(2)
       setgid32(2)		   2.4
       setgroups(2)
       setgroups32(2)		   2.4
       sethostname(2)
       setitimer(2)
       setpgid(2)
       setpriority(2)
       setregid(2)
       setregid32(2)		   2.4
       setresgid(2)		   2.2
       setresgid32(2)		   2.4
       setresuid(2)		   2.2
       setresuid32(2)		   2.4
       setreuid(2)
       setreuid32(2)		   2.4
       setrlimit(2)
       setsid(2)

       setsockopt(2)
       settimeofday(2)
       setuid(2)
       setuid32(2)		   2.4
       setup(2)					 Removed in 2.2
       setxattr(2)		   2.6; 2.4.18
       sgetmask(2)
       shmat(2)
       shmctl(2)
       shmdt(2)
       shmget(2)
       shutdown(2)
       sigaction(2)
       sigaltstack(2)		   2.2
       signal(2)
       signalfd(2)		   2.6.22
       signalfd4(2)		   2.6.27
       sigpending(2)
       sigprocmask(2)
       sigreturn(2)
       sigsuspend(2)
       socket(2)
       socketcall(2)
       socketpair(2)
       splice(2)		   2.6.17
       spu_create(2)		   2.6.16	 PowerPC only
       spu_run(2)		   2.6.16	 PowerPC only
       ssetmask(2)
       stat(2)
       stat64(2)		   2.4
       statfs(2)
       statfs64(2)		   2.6
       stime(2)
       stty(2)					 Not implemented
       swapoff(2)
       swapon(2)
       symlink(2)
       symlinkat(2)		   2.6.16
       sync(2)
       sync_file_range(2)	   2.6.17
       sysfs(2)			   1.2
       sysinfo(2)
       syslog(2)
       tee(2)			   2.6.17
       tgkill(2)		   2.6
       time(2)
       timer_create(2)		   2.6
       timer_delete(2)		   2.6
       timer_getoverrun(2)	   2.6
       timer_gettime(2)		   2.6
       timer_settime(2)		   2.6
       timerfd_create(2)	   2.6.25
       timerfd_gettime(2)	   2.6.25
       timerfd_settime(2)	   2.6.25
       times(2)
       tkill(2)			   2.6; 2.4.22
       truncate(2)
       truncate64(2)		   2.4
       tuxcall(2)				 Not implemented
       ugetrlimit(2)		   2.4
       ulimit(2)				 Not implemented
       umask(2)
       umount(2)
       umount2(2)		   2.2
       uname(2)

       unlink(2)
       unlinkat(2)		   2.6.16
       unshare(2)		   2.6.16
       uselib(2)
       ustat(2)
       utime(2)
       utimensat(2)		   2.6.22
       utimes(2)		   2.6
       vfork(2)
       vhangup(2)
       vm86old(2)
       vmsplice(2)		   2.6.17
       vserver(2)				 Not implemented
       wait4(2)
       waitid(2)		   2.6.10
       waitpid(2)
       write(2)
       writev(2)		   2.0

       On  many	 platforms,  including	i386, socket calls are all multiplexed
       (via glibc wrapper functions) through socketcall(2) and similarly  Sys‐
       tem V IPC calls are multiplexed through ipc(2).

NOTES
       Note the following points:

       *  Although  slots  are reserved for them in the system call table, the
	  following system calls are not implemented in the  standard  kernel:
	  afs_syscall(2),  break(2),  ftime(2),	 getpmsg(2), gtty(2), idle(2),
	  lock(2),   madvise1(2),   mpx(2),   phys(2),	 prof(2),   profil(2),
	  putpmsg(2),	security(2),   stty(2),	  tuxcall(2),  ulimit(2),  and
	  vserver(2) (see also	unimplemented(2)).   However,  ftime(3),  pro‐
	  fil(3)  and  ulimit(3)  exist	 as  library  routines.	  The slot for
	  phys(2) is in use since kernel 2.1.116 for umount(2);	 phys(2)  will
	  never be implemented.

       *  The  getpmsg(2) and putpmsg(2) calls are for kernels patched to sup‐
	  port STREAMS, and may never be in the standard kernel.

       Roughly speaking, the code belonging to the  system  call  with	number
       __NR_xxx	 defined in /usr/include/asm/unistd.h can be found in the ker‐
       nel source in the routine sys_xxx().  (The dispatch table for i386  can
       be  found  in /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., truncate(2) and 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:

       *  By  now  there  are  three different versions of stat(2): sys_stat()
	  (slot	  __NR_oldstat),   sys_newstat()   (slot    __NR_stat),	   and
	  sys_stat64()	(slot  __NR_stat64), with the last being the most cur‐
	  rent.	 A similar story applies for lstat(2) and fstat(2).

       *  Similarly,  the   defines   __NR_oldolduname,	  __NR_olduname,   and
	  __NR_uname  refer  to	 the  routines sys_olduname(), sys_uname() and
	  sys_newuname().

       *  In Linux 2.0, a new version of vm86(2) appeared, with	 the  old  and
	  the new kernel routines being named sys_vm86old() and sys_vm86().

       *  In  Linux  2.4, a new version of getrlimit(2) appeared, with the old
	  and the new kernel routines being  named  sys_old_getrlimit()	 (slot
	  __NR_getrlimit) and sys_getrlimit() (slot __NR_ugetrlimit).

       *  Linux	 2.4  increased	 the  size of user and group IDs from 16 to 32
	  bits.	 To support this change, a range of system  calls  were	 added
	  (e.g.,  chown32(2),  getuid32(2),  getgroups32(2),  setresuid32(2)),
	  superseding earlier calls of the same name without the "32" suffix.

       *  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,  replace‐
	  ments were required for system calls that deal with file offsets and
	  sizes.  Thus the following  system  calls  were  added:  fcntl64(2),
	  ftruncate64(2),  getdents64(2),  stat64(2),  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"  suf‐
	  fix.

	  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.

       *  The  rt_sig*	calls were added in kernel 2.2 to support the addition
	  of real-time signals (see signal(7)).	 These system calls  supersede
	  the older system calls of the same name without the "rt_" prefix.

       *  The  select(2)  and 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 sys_select() and
	  sys_mmap() corresponding to __NR_select and __NR_mmap, on  i386  one
	  finds	 old_select() and 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 __NR__newselect that corresponds
	  directly to sys_select() and similarly __NR_mmap2.

SEE ALSO
       syscall(2), unimplemented(2), libc(7)

COLOPHON
       This page is part of release 3.22 of the Linux  man-pages  project.   A
       description  of	the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.

Linux				  2009-05-06			   SYSCALLS(2)
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