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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 copy-
       ing arguments to the right registers before invoking the system call, and then set-
       ting  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 wrapper 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 positive), 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 truncate64(2), and the glibc truncate() wrap-
       per  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  fol-
       lowing 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 probably 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 initiated 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 probably 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 initiated 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 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 2.6.28 (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 System V IPC calls are mul-
       tiplexed 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 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  rou-
       tine    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 func-
       tions 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_old-
          stat), 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 sup-
          port 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 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()  (rou-
          tines  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  corre-
          sponds 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.ker-
       nel.org/doc/man-pages/.



Linux                             2009-05-06                       SYSCALLS(2)

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