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SYSCALLS(2)		   Linux Programmers 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
       before invoking the system call.

       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 2.6.25 (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)
       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)
       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)
       epoll_create(2)		   2.6
       epoll_ctl(2)		   2.6
       epoll_pwait(2)		   2.6.19
       epoll_wait(2)		   2.6
       eventfd(2)		   2.6.22
       execve(2)
       exit(2)
       exit_group(2)		   2.6; 2.4.20
       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; 2.4.19
       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; 2.4.20
       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)
       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_rm_watch(2)	   2.6.13
       io_cancel(2)		   2.6; 2.4.20
       io_destroy(2)		   2.6; 2.4.20
       io_getevents(2)		   2.6; 2.4.20
       io_setup(2)		   2.6; 2.4.20
       io_submit(2)		   2.6; 2.4.20
       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)
       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
       prof(2)					 Not implemented
       profil(2)				 Not implemented
       pselect6(2)		   2.6.16
       ptrace(2)
       putpmsg(2)
       pwrite64(2)				 Added as "pwrite" in 2.2;
						 renamed "pwrite64" in 2.6
       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; 2.4.19
       sched_getparam(2)	   2.0
       sched_getscheduler(2)	   2.0
       sched_rr_get_interval(2)    2.0

       sched_setaffinity(2)	   2.6; 2.4.19
       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; 2.4.20
       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
       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
	  cant	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)

COLOPHON
       This  page  is  part of release 3.05 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				  2008-06-19			   SYSCALLS(2)




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