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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
       truncate64(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
       platforms.  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 2.0 or earlier.

       *  Where  a  system  call  is  marked  "2.2" this means the system call
          probably 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
          initiated 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
          probably 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
          initiated 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
          probably 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 2.6.22 (or  in
       a few cases only on older kernels) is as follows:

       System call                 Kernel        Notes
       -----------------------------------------------------------------------

       _llseek(2)
       _newselect(2)
       _sysctl(2)
       accept(2)
       access(2)
       acct(2)
       add_key(2)                  2.6.11
       adjtimex(2)
       afs_syscall(2)
       alarm(2)
       alloc_hugepages(2)          2.5.36        Removed in 2.5.44
       bdflush(2)
       bind(2)
       break(2)
       brk(2)
       cacheflush(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)
       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)
       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)
       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)                            Not on i386
       getpgid(2)
       getpgrp(2)
       getpid(2)
       getpmsg(2)                  2.2
       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)
       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)
       idle(2)
       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)
       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)
       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)
       msgctl(2)
       msgget(2)
       msgrcv(2)
       msgsnd(2)
       msync(2)
       munlock(2)
       munlockall(2)
       munmap(2)
       nanosleep(2)
       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)
       phys(2)
       pipe(2)
       pivot_root(2)               2.5
       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)
       profil(2)
       pselect6(2)                 2.6.16
       ptrace(2)
       putpmsg(2)                  2.2
       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)
       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)
       sched_get_priority_min(2)
       sched_getaffinity(2)        2.6; 2.4.19
       sched_getparam(2)
       sched_getscheduler(2)
       sched_rr_get_interval(2)
       sched_setaffinity(2)        2.6; 2.4.19
       sched_setparam(2)
       sched_setscheduler(2)
       sched_yield(2)
       security(2)                 2.4.11
       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)
       setfsgid32(2)               2.4
       setfsuid(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)
       swapoff(2)
       swapon(2)
       symlink(2)
       symlinkat(2)                2.6.16
       sync(2)
       sync_file_range(2)          2.6.17
       sysfs(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
       times(2)
       tkill(2)                    2.6; 2.4.22
       truncate(2)
       truncate64(2)               2.4
       tuxcall(2)
       ugetrlimit(2)               2.4
       ulimit(2)
       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)                  2.6
       wait4(2)
       waitid(2)                   2.6.10
       waitpid(2)
       write(2)
       writev(2)

       On  many  platforms,  including  i386, socket calls are all multiplexed
       (via glibc  wrapper  functions)  through  socketcall(2)  and  similarly
       System 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),
          profil(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
          support 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
       kernel 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 ftruncate64(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
          current.  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,
          replacements 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"
          suffix.

          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  parameters,
          which  caused problems the way parameter 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
          parameter block) instead.  These days passing five parameters 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 2.77 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/.