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

       syscalls - Linux system calls

       Linux system calls.

       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

       *  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

       *  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

       *  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

       *  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:

       l l l --- l l l.  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_get-
       time(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 fad-
       vise64(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  fchow-
       nat(2)    2.6.16  fcntl(2)   fcntl64(2)     2.4   fdatasync(2)   fgetx-
       attr(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      fremovex-
       attr(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_mem-
       policy(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    get-
       dents64(2)  2.4      getegid(2)      getegid32(2)   2.4      geteuid(2)
       geteuid32(2)   2.4  getgid(2)  getgid32(2)    2.4   getgroups(2)   get-
       groups32(2) 2.4  getitimer(2) getpeername(2) getpagesize(2) 2.0  Not on
       i386 getpgid(2) getpgrp(2) getpid(2)  getpmsg(2)  getppid(2)  getprior-
       ity(2)  getresgid(2)   2.2 getresgid32(2) 2.4 getresuid(2)   2.2 getre-
       suid32(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 imple-
       mented     idle(2)        Not     implemented    init_module(2)    ino-
       tify_add_watch(2)     2.6.13      inotify_init(2)     2.6.13       ino-
       tify_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  lgetx-
       attr(2)   2.6;  2.4.18  link(2)   linkat(2) 2.6.16   listen(2)   listx-
       attr(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 mad-
       vise(2)     2.4           madvise1(2)    2.4            mbind(2)  2.6.6
       migrate_pages(2)    2.6.16     mincore(2)     2.4     mkdir(2)    mkdi-
       rat(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)  ope-
       nat(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     pcicon-
       fig_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)    read-
       linkat(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_sigproc-
       mask(2)   2.2 rt_sigqueueinfo(2)  2.2  rt_sigreturn(2)     2.2  rt_sig-
       suspend(2)    2.2        rt_sigtimedwait(2)  2.2       sched_get_prior-
       ity_max(2)     2.0  sched_get_priority_min(2)     2.0   sched_getaffin-
       ity(2)     2.6;    2.4.19    sched_getparam(2)   2.0    sched_getsched-
       uler(2)    2.0       sched_rr_get_interval(2) 2.0       sched_setaffin-
       ity(2)     2.6;    2.4.19    sched_setparam(2)   2.0    sched_setsched-
       uler(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) set-
       gid32(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    setre-
       suid32(2) 2.4  setreuid(2)  setreuid32(2)  2.4  setrlimit(2)  setsid(2)
       setsockopt(2)   settimeofday(2)   setuid(2)   setuid32(2)    2.4   set-
       up(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)  sigalt-
       stack(2) 2.2  signal(2)  signalfd(2)    2.6.22  sigpending(2)  sigproc-
       mask(2)  sigreturn(2)  sigsuspend(2)  socket(2)  socketcall(2)  socket-
       pair(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_get-
       time(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  imple-
       mented   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  wait-
       pid(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).

       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

       *  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-

          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.

       syscall(2), unimplemented(2)

       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)