syscalls(2)



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 di-
       rect 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  chdir()
       which invokes the underlying "chdir" system call.

       Often the glibc wrapper function is quite thin, doing little work other
       than copying arguments to the right registers before invoking the  sys-
       tem  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 wrap-
       per function is provided.)  Note: system calls indicate  a  failure  by
       returning  a negative error number to the caller on architectures with-
       out a separate error register/flag, as noted in syscall(2);  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 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 the Linux system calls.  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 se-
          ries.)

       *  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 se-
          ries.)

       *  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 se-
          ries.)

       *  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; and the 4.x kernel  series,  which  followed  on
          from  kernel 3.19; and the 5.x kernel series, which followed on from
          kernel 4.20.

       *  In some cases, a system call was added to a stable kernel series af-
          ter  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 4.19 (or in a
       few cases only on older kernels) is as follows:

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

       _llseek(2)                 1.2
       _newselect(2)              2.0
       _sysctl(2)                 2.0
       accept(2)                  2.0           See notes on socketcall(2)
       accept4(2)                 2.6.28
       access(2)                  1.0
       acct(2)                    1.0
       add_key(2)                 2.6.10
       adjtimex(2)                1.0
       alarm(2)                   1.0
       alloc_hugepages(2)         2.5.36        Removed in 2.5.44
       arc_gettls(2)              3.9           ARC only
       arc_settls(2)              3.9           ARC only
       arc_usr_cmpxchg(2)         4.9           ARC only
       arch_prctl(2)              2.6           x86_64, x86 since 4.12
       atomic_barrier(2)          2.6.34        m68k only
       atomic_cmpxchg_32(2)       2.6.34        m68k only
       bdflush(2)                 1.2           Deprecated (does nothing)
                                                since 2.6
       bfin_spinlock(2)           2.6.22        Blackfin only (port removed
                                                in Linux 4.17)
       bind(2)                    2.0           See notes on socketcall(2)
       bpf(2)                     3.18
       brk(2)                     1.0
       breakpoint(2)              2.2           ARM OABI only, defined with
                                                __ARM_NR prefix
       cacheflush(2)              1.2           Not on x86
       capget(2)                  2.2
       capset(2)                  2.2
       chdir(2)                   1.0

       chmod(2)                   1.0
       chown(2)                   2.2           See chown(2) for
                                                version details
       chown32(2)                 2.4
       chroot(2)                  1.0
       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
       clone2(2)                  2.4           IA-64 only
       clone(2)                   1.0
       clone3(2)                  5.3
       close(2)                   1.0
       cmpxchg_badaddr(2)         2.6.36        Tile only (port removed
                                                in Linux 4.17)
       connect(2)                 2.0           See notes on socketcall(2)
       copy_file_range(2)         4.5
       creat(2)                   1.0
       create_module(2)           1.0           Removed in 2.6
       delete_module(2)           1.0
       dma_memcpy(2)              2.6.22        Blackfin only (port removed
                                                in Linux 4.17)
       dup(2)                     1.0
       dup2(2)                    1.0
       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
       execv(2)                   2.0           SPARC/SPARC64 only, for
                                                compatibility with SunOS
       execve(2)                  1.0
       execveat(2)                3.19
       exit(2)                    1.0
       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)                  1.0
       fchmod(2)                  1.0
       fchmodat(2)                2.6.16
       fchown(2)                  1.0
       fchown32(2)                2.4
       fchownat(2)                2.6.16
       fcntl(2)                   1.0
       fcntl64(2)                 2.4
       fdatasync(2)               2.0
       fgetxattr(2)               2.6; 2.4.18
       finit_module(2)            3.8
       flistxattr(2)              2.6; 2.4.18
       flock(2)                   2.0
       fork(2)                    1.0
       free_hugepages(2)          2.5.36        Removed in 2.5.44
       fremovexattr(2)            2.6; 2.4.18
       fsconfig(2)                5.2
       fsetxattr(2)               2.6; 2.4.18
       fsmount(2)                 5.2
       fsopen(2)                  5.2

       fspick(2)                  5.2
       fstat(2)                   1.0
       fstat64(2)                 2.4
       fstatat64(2)               2.6.16
       fstatfs(2)                 1.0
       fstatfs64(2)               2.6
       fsync(2)                   1.0
       ftruncate(2)               1.0
       ftruncate64(2)             2.4
       futex(2)                   2.6
       futimesat(2)               2.6.16
       get_kernel_syms(2)         1.0           Removed in 2.6
       get_mempolicy(2)           2.6.6
       get_robust_list(2)         2.6.17
       get_thread_area(2)         2.6
       get_tls(2)                 4.15          ARM OABI only, has
                                                __ARM_NR prefix
       getcpu(2)                  2.6.19
       getcwd(2)                  2.2
       getdents(2)                2.0
       getdents64(2)              2.4
       getdomainname(2)           2.2           SPARC, SPARC64; available
                                                as osf_getdomainname(2)
                                                on Alpha since Linux 2.0
       getdtablesize(2)           2.0           SPARC (removed in 2.6.26),
                                                available on Alpha as
                                                osf_getdtablesize(2)
       getegid(2)                 1.0
       getegid32(2)               2.4
       geteuid(2)                 1.0
       geteuid32(2)               2.4
       getgid(2)                  1.0
       getgid32(2)                2.4
       getgroups(2)               1.0
       getgroups32(2)             2.4
       gethostname(2)             2.0           Alpha, was available on
                                                SPARC up to Linux 2.6.26
       getitimer(2)               1.0
       getpeername(2)             2.0           See notes on socketcall(2)
       getpagesize(2)             2.0           Not on x86
       getpgid(2)                 1.0
       getpgrp(2)                 1.0
       getpid(2)                  1.0
       getppid(2)                 1.0
       getpriority(2)             1.0
       getrandom(2)               3.17
       getresgid(2)               2.2
       getresgid32(2)             2.4
       getresuid(2)               2.2
       getresuid32(2)             2.4
       getrlimit(2)               1.0
       getrusage(2)               1.0
       getsid(2)                  2.0
       getsockname(2)             2.0           See notes on socketcall(2)
       getsockopt(2)              2.0           See notes on socketcall(2)
       gettid(2)                  2.4.11
       gettimeofday(2)            1.0
       getuid(2)                  1.0
       getuid32(2)                2.4
       getunwind(2)               2.4.8         IA-64 only; deprecated
       getxattr(2)                2.6; 2.4.18
       getxgid(2)                 2.0           Alpha only; see NOTES
       getxpid(2)                 2.0           Alpha only; see NOTES
       getxuid(2)                 2.0           Alpha only; see NOTES
       init_module(2)             1.0

       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_pgetevents(2)           4.18
       io_setup(2)                2.6
       io_submit(2)               2.6
       io_uring_enter(2)          5.1
       io_uring_register(2)       5.1
       io_uring_setup(2)          5.1
       ioctl(2)                   1.0
       ioperm(2)                  1.0
       iopl(2)                    1.0
       ioprio_get(2)              2.6.13
       ioprio_set(2)              2.6.13
       ipc(2)                     1.0
       kcmp(2)                    3.5
       kern_features(2)           3.7           SPARC64 only
       kexec_file_load(2)         3.17
       kexec_load(2)              2.6.13
       keyctl(2)                  2.6.10
       kill(2)                    1.0
       lchown(2)                  1.0           See chown(2) for
                                                version details
       lchown32(2)                2.4
       lgetxattr(2)               2.6; 2.4.18
       link(2)                    1.0
       linkat(2)                  2.6.16
       listen(2)                  2.0           See notes on socketcall(2)
       listxattr(2)               2.6; 2.4.18
       llistxattr(2)              2.6; 2.4.18
       lookup_dcookie(2)          2.6
       lremovexattr(2)            2.6; 2.4.18
       lseek(2)                   1.0
       lsetxattr(2)               2.6; 2.4.18
       lstat(2)                   1.0
       lstat64(2)                 2.4
       madvise(2)                 2.4
       mbind(2)                   2.6.6
       memory_ordering(2)         2.2           SPARC64 only
       metag_get_tls(2)           3.9           Metag only (port removed
                                                in Linux 4.17)
       metag_set_fpu_flags(2)     3.9           Metag only (port removed
                                                in Linux 4.17)
       metag_set_tls(2)           3.9           Metag only (port removed
                                                in Linux 4.17)
       metag_setglobalbit(2)      3.9           Metag only (port removed
                                                in Linux 4.17)
       membarrier(2)              3.17
       memfd_create(2)            3.17
       migrate_pages(2)           2.6.16
       mincore(2)                 2.4
       mkdir(2)                   1.0
       mkdirat(2)                 2.6.16
       mknod(2)                   1.0
       mknodat(2)                 2.6.16
       mlock(2)                   2.0
       mlock2(2)                  4.4
       mlockall(2)                2.0
       mmap(2)                    1.0
       mmap2(2)                   2.4
       modify_ldt(2)              1.0

       mount(2)                   1.0
       move_mount(2)              5.2
       move_pages(2)              2.6.18
       mprotect(2)                1.0
       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)               2.6.6
       mremap(2)                  2.0
       msgctl(2)                  2.0           See notes on ipc(2)
       msgget(2)                  2.0           See notes on ipc(2)
       msgrcv(2)                  2.0           See notes on ipc(2)
       msgsnd(2)                  2.0           See notes on ipc(2)
       msync(2)                   2.0
       munlock(2)                 2.0
       munlockall(2)              2.0
       munmap(2)                  1.0
       name_to_handle_at(2)       2.6.39
       nanosleep(2)               2.0
       newfstatat(2)              2.6.16        See stat(2)
       nfsservctl(2)              2.2           Removed in 3.1
       nice(2)                    1.0
       old_adjtimex(2)            2.0           Alpha only; see NOTES
       old_getrlimit(2)           2.4           Old variant of getrlimit(2)
                                                that used a different value
                                                for RLIM_INFINITY
       oldfstat(2)                1.0
       oldlstat(2)                1.0
       oldolduname(2)             1.0
       oldstat(2)                 1.0
       oldumount(2)               2.4.116       Name of the old umount(2)
                                                syscall on Alpha
       olduname(2)                1.0
       open(2)                    1.0
       open_by_handle_at(2)       2.6.39
       open_tree(2)               5.2
       openat(2)                  2.6.16
       openat2(2)                 5.6
       or1k_atomic(2)             3.1           OpenRISC 1000 only
       pause(2)                   1.0
       pciconfig_iobase(2)        2.2.15; 2.4   Not on x86
       pciconfig_read(2)          2.0.26; 2.2   Not on x86
       pciconfig_write(2)         2.0.26; 2.2   Not on x86
       perf_event_open(2)         2.6.31        Was perf_counter_open() in
                                                2.6.31; renamed in 2.6.32
       personality(2)             1.2
       perfctr(2)                 2.2           SPARC only; removed in 2.6.34
       perfmonctl(2)              2.4           IA-64 only
       pidfd_getfd(2)             5.6
       pidfd_send_signal(2)       5.1
       pidfd_open(2)              5.3
       pipe(2)                    1.0
       pipe2(2)                   2.6.27
       pivot_root(2)              2.4
       pkey_alloc(2)              4.8
       pkey_free(2)               4.8
       pkey_mprotect(2)           4.8
       poll(2)                    2.0.36; 2.2
       ppoll(2)                   2.6.16
       prctl(2)                   2.2

       pread(2)                                 Used for pread64(2) on AVR32
                                                (port removed in Linux 4.12)
                                                and Blackfin (port removed
                                                in Linux 4.17)
       pread64(2)                               Added as "pread" in 2.2;
                                                renamed "pread64" in 2.6
       preadv(2)                  2.6.30
       preadv2(2)                 4.6
       prlimit64(2)               2.6.36
       process_vm_readv(2)        3.2
       process_vm_writev(2)       3.2
       pselect6(2)                2.6.16
       ptrace(2)                  1.0
       pwrite(2)                                Used for pwrite64(2)
                                                on AVR32 (port removed
                                                in Linux 4.12) and Blackfin
                                                (port removed in Linux 4.17)
       pwrite64(2)                              Added as "pwrite" in 2.2;
                                                renamed "pwrite64" in 2.6
       pwritev(2)                 2.6.30
       pwritev2(2)                4.6
       query_module(2)            2.2           Removed in 2.6
       quotactl(2)                1.0
       read(2)                    1.0
       readahead(2)               2.4.13
       readdir(2)                 1.0
       readlink(2)                1.0
       readlinkat(2)              2.6.16
       readv(2)                   2.0
       reboot(2)                  1.0
       recv(2)                    2.0           See notes on socketcall(2)
       recvfrom(2)                2.0           See notes on socketcall(2)
       recvmsg(2)                 2.0           See notes on socketcall(2)
       recvmmsg(2)                2.6.33
       remap_file_pages(2)        2.6           Deprecated since 3.16
       removexattr(2)             2.6; 2.4.18
       rename(2)                  1.0
       renameat(2)                2.6.16
       renameat2(2)               3.15
       request_key(2)             2.6.10
       restart_syscall(2)         2.6
       riscv_flush_icache(2)      4.15          RISC-V only
       rmdir(2)                   1.0
       rseq(2)                    4.18
       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
       rtas(2)                    2.6.2         PowerPC/PowerPC64 only
       s390_runtime_instr(2)      3.7           s390 only
       s390_pci_mmio_read(2)      3.19          s390 only
       s390_pci_mmio_write(2)     3.19          s390 only
       s390_sthyi(2)              4.15          s390 only
       s390_guarded_storage(2)    4.12          s390 only
       sched_get_affinity(2)      2.6           Name of sched_getaffinity(2)
                                                on SPARC and SPARC64
       sched_get_priority_max(2)  2.0
       sched_get_priority_min(2)  2.0
       sched_getaffinity(2)       2.6
       sched_getattr(2)           3.14
       sched_getparam(2)          2.0

       sched_getscheduler(2)      2.0
       sched_rr_get_interval(2)   2.0
       sched_set_affinity(2)      2.6           Name of sched_setaffinity(2)
                                                on SPARC and SPARC64
       sched_setaffinity(2)       2.6
       sched_setattr(2)           3.14
       sched_setparam(2)          2.0
       sched_setscheduler(2)      2.0
       sched_yield(2)             2.0
       seccomp(2)                 3.17
       select(2)                  1.0
       semctl(2)                  2.0           See notes on ipc(2)
       semget(2)                  2.0           See notes on ipc(2)
       semop(2)                   2.0           See notes on ipc(2)
       semtimedop(2)              2.6; 2.4.22
       send(2)                    2.0           See notes on socketcall(2)
       sendfile(2)                2.2
       sendfile64(2)              2.6; 2.4.19
       sendmmsg(2)                3.0
       sendmsg(2)                 2.0           See notes on socketcall(2)
       sendto(2)                  2.0           See notes on socketcall(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_tls(2)                 2.6.11        ARM OABI/EABI only (constant
                                                has __ARM_NR prefix)
       setdomainname(2)           1.0
       setfsgid(2)                1.2
       setfsgid32(2)              2.4
       setfsuid(2)                1.2
       setfsuid32(2)              2.4
       setgid(2)                  1.0
       setgid32(2)                2.4
       setgroups(2)               1.0
       setgroups32(2)             2.4
       sethae(2)                  2.0           Alpha only; see NOTES
       sethostname(2)             1.0
       setitimer(2)               1.0
       setns(2)                   3.0
       setpgid(2)                 1.0
       setpgrp(2)                 2.0           Alternative name for
                                                setpgid(2) on Alpha
       setpriority(2)             1.0
       setregid(2)                1.0
       setregid32(2)              2.4
       setresgid(2)               2.2
       setresgid32(2)             2.4
       setresuid(2)               2.2
       setresuid32(2)             2.4
       setreuid(2)                1.0
       setreuid32(2)              2.4
       setrlimit(2)               1.0
       setsid(2)                  1.0
       setsockopt(2)              2.0           See notes on socketcall(2)
       settimeofday(2)            1.0
       setuid(2)                  1.0
       setuid32(2)                2.4
       setup(2)                   1.0           Removed in 2.2
       setxattr(2)                2.6; 2.4.18
       sgetmask(2)                1.0
       shmat(2)                   2.0           See notes on ipc(2)
       shmctl(2)                  2.0           See notes on ipc(2)
       shmdt(2)                   2.0           See notes on ipc(2)
       shmget(2)                  2.0           See notes on ipc(2)

       shutdown(2)                2.0           See notes on socketcall(2)
       sigaction(2)               1.0
       sigaltstack(2)             2.2
       signal(2)                  1.0
       signalfd(2)                2.6.22
       signalfd4(2)               2.6.27
       sigpending(2)              1.0
       sigprocmask(2)             1.0
       sigreturn(2)               1.0
       sigsuspend(2)              1.0
       socket(2)                  2.0           See notes on socketcall(2)
       socketcall(2)              1.0
       socketpair(2)              2.0           See notes on socketcall(2)
       spill(2)                   2.6.13        Xtensa only
       splice(2)                  2.6.17
       spu_create(2)              2.6.16        PowerPC/PowerPC64 only
       spu_run(2)                 2.6.16        PowerPC/PowerPC64 only
       sram_alloc(2)              2.6.22        Blackfin (port removed
                                                in Linux 4.17)
       sram_free(2)               2.6.22        Blackfin (port removed
                                                in Linux 4.17)
       ssetmask(2)                1.0
       stat(2)                    1.0
       stat64(2)                  2.4
       statfs(2)                  1.0
       statfs64(2)                2.6
       statx(2)                   4.11
       stime(2)                   1.0
       subpage_prot(2)            2.6.25        PowerPC/PowerPC64 only
       swapcontext(2)             2.6.3         PowerPC/PowerPC64 only
       switch_endian(2)           4.1           PowerPC64 only
       swapcontext(2)             2.6.3         PowerPC only
       swapoff(2)                 1.0
       swapon(2)                  1.0
       symlink(2)                 1.0
       symlinkat(2)               2.6.16
       sync(2)                    1.0
       sync_file_range(2)         2.6.17
       sync_file_range2(2)        2.6.22
       syncfs(2)                  2.6.39
       sys_debug_setcontext(2)    2.6.11        PowerPC only
       syscall(2)                 1.0           Still available on ARM OABI
                                                and MIPS O32 ABI
       sysfs(2)                   1.2
       sysinfo(2)                 1.0
       syslog(2)                  1.0
       sysmips(2)                 2.6.0         MIPS only
       tee(2)                     2.6.17
       tgkill(2)                  2.6
       time(2)                    1.0
       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)                   1.0
       tkill(2)                   2.6; 2.4.22
       truncate(2)                1.0
       truncate64(2)              2.4
       ugetrlimit(2)              2.4
       umask(2)                   1.0
       umount(2)                  1.0

       umount2(2)                 2.2
       uname(2)                   1.0
       unlink(2)                  1.0
       unlinkat(2)                2.6.16
       unshare(2)                 2.6.16
       uselib(2)                  1.0
       ustat(2)                   1.0
       userfaultfd(2)             4.3
       usr26(2)                   2.4.8.1       ARM OABI only
       usr32(2)                   2.4.8.1       ARM OABI only
       utime(2)                   1.0
       utimensat(2)               2.6.22
       utimes(2)                  2.2
       utrap_install(2)           2.2           SPARC64 only
       vfork(2)                   2.2
       vhangup(2)                 1.0
       vm86old(2)                 1.0           Was "vm86"; renamed in
                                                2.0.28/2.2
       vm86(2)                    2.0.28; 2.2
       vmsplice(2)                2.6.17
       wait4(2)                   1.0
       waitid(2)                  2.6.10
       waitpid(2)                 1.0
       write(2)                   1.0
       writev(2)                  2.0
       xtensa(2)                  2.6.13        Xtensa only

       On many platforms, including x86-32, socket calls are  all  multiplexed
       (via  glibc wrapper functions) through socketcall(2) and similarly Sys-
       tem V IPC calls are multiplexed through ipc(2).

       Although slots are reserved for them in the system call table, the fol-
       lowing  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.

       There  was  briefly set_zone_reclaim(2), added in Linux 2.6.13, and re-
       moved in 2.6.16; this system call was never available to user space.

NOTES
       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 Linux
       kernel source in the routine sys_xxx().   There  are  many  exceptions,
       however,  mostly  because  older  system calls were superseded by newer
       ones, and this has been treated somewhat  unsystematically.   On  plat-
       forms  with  proprietary  operating-system  emulation,  such  as 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, certain architectures (notably,  longstanding  32-bit
       architectures  such  as i386) now have 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  bina-
       ries.)   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_un-
          ame refer to the routines sys_olduname(), sys_uname() and  sys_newu-
          name().

       *  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)), su-
          perseding 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), get-
          dents64(2), stat64(2), statfs64(2), truncate64(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/GIDs (e.g., alpha, ia64, s390x, x86-64), there is just a single
          version  of  the UID/GID and file access system calls.  On platforms
          (typically, 32-bit platforms) 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 in 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 an
          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.   s390x  is  the
          only 64-bit architecture that has old_mmap().

   Architecture-specific details: Alpha
       *  getxgid(2)  returns a pair of GID and effective GID via registers r0
          and r20; it is provided instead of getgid(2) and getegid(2).

       *  getxpid(2) returns a pair of PID and parent PID via registers r0 and
          r20; it is provided instead of getpid(2) and getppid(2).

       *  old_adjtimex(2)  is  a  variant  of  adjtimex(2)  that  uses  struct
          timeval32, for compatibility with OSF/1.

       *  getxuid(2) returns a pair of GID and effective GID via registers  r0
          and r20; it is provided instead of getuid(2) and geteuid(2).

       *  sethae(2)  is used for configuring the Host Address Extension regis-
          ter on low-cost Alphas in order to access address space beyond first
          27 bits.

SEE ALSO
       intro(2), syscall(2), unimplemented(2), errno(3), libc(7), vdso(7)

COLOPHON
       This  page  is  part of release 5.07 of the Linux man-pages project.  A
       description of the project, information about reporting bugs,  and  the
       latest     version     of     this    page,    can    be    found    at
       https://www.kernel.org/doc/man-pages/.

Linux                             2020-04-11                       SYSCALLS(2)

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