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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 other than copying
       arguments to the right registers before invoking the system 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  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()  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  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.  This convention continues with the 3.x  kernel  series,  which
          followed on from kernel 2.6.39.

       *  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 3.1 (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)
       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_adjtime(2)            2.6.39
       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
       fanotify_init(2)            2.6.37
       fanotify_mark(2)            2.6.37
       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)               2.6.13
       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)
       name_to_handle_at(2)        2.6.39
       nanosleep(2)                2.0
       nfsservctl(2)               2.2
       nice(2)
       oldfstat(2)
       oldlstat(2)
       oldolduname(2)
       oldstat(2)
       olduname(2)
       open(2)
       open_by_handle_at(2)        2.6.39
       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
       perf_event_open(2)          2.6.31        Was called perf_counter_open()
                                                 in 2.6.31; renamed in 2.6.32
       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
       prlimit(2)                  2.6.36
       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)
       recvmmsg(2)                 2.6.33
       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
       rt_tgsigqueueinfo(2)        2.6.31
       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
       sendmmsg(2)                 3.0
       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)
       setns(2)                    3.0
       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
       subpage_prot(2)             2.6.25        PowerPC if CONFIG_PPC_64K_PAGES
       swapoff(2)
       swapon(2)
       symlink(2)
       symlinkat(2)                2.6.16
       sync(2)
       sync_file_range(2)          2.6.17
       sync_file_range2(2)         2.6.22        Architecture-specific variant
       syncfs(2)                   2.6.39
                                                 of sync_file_range(2)
       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)                   2.2
       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 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 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 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  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 3.35 of the Linux man-pages project.  A  description  of  the
       project,  and information about reporting bugs, can be found at http://man7.org/linux/man-
       pages/.