SYSCALLS(2)               (2020-12-21)                SYSCALLS(2)

          syscalls - Linux system calls

          Linux system calls.

          The system call is the fundamental interface between an
          application and the Linux kernel.

        System calls and library wrapper functions
          System calls are generally not invoked directly, but rather
          via wrapper functions in glibc (or perhaps some other
          library).  For details of direct invocation of a system
          call, see intro(2).  Often, but not always, the name of the
          wrapper function is the same as the name of the system call
          that it invokes.  For example, glibc contains a function
          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 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 fail-
          ure by returning a negative error number to the caller on
          architectures without 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

          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 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.

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          *  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.  (Develop-
             ment 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.  (Develop-
             ment 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.  (Develop-
             ment 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 con-
             tinues 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 after it branched from the previous stable kernel
             series, and then backported into the earlier stable ker-
             nel 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

          The list of system calls that are available as at kernel
          5.10 (or in a few cases only on older kernels) is as fol-
          lows: l2 le l --- l l l.  System call    Kernel    Notes

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          _llseek(2)     1.2 _newselect(2)  2.0
          _sysctl(2)     2.0  Removed in 5.5 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  T{ Deprecated (does nothing)
          since 2.6 T} bind(2)   2.0  See notes on socketcall(2)
          bpf(2)    3.18 brk(2)    1.0 breakpoint(2)  2.2  T{ ARM OABI
          only, defined with
          __ARM_NR prefix T} cacheflush(2)  1.2  Not on x86 cap-
          get(2) 2.2 capset(2) 2.2 chdir(2)  1.0 chmod(2)  1.0
          chown(2)  2.2  T{ See chown(2) for
          version details T} 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 close_range(2) 5.9
          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 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  T{ SPARC/SPARC64 only, for
          compatibility with SunOS T} execve(2) 1.0
          execveat(2)    3.19 exit(2)   1.0 exit_group(2)  2.6 facces-
          sat(2)   2.6.16 faccessat2(2)  5.8 fadvise64(2)   2.6 fad-
          vise64_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 fgetx-
          attr(2)   2.6; 2.4.18 finit_module(2)     3.8 flistx-
          attr(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 fremovex-
          attr(2)     2.6; 2.4.18 fsconfig(2)    5.2 fsetx-
          attr(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 T{ ARM OABI
          only, has

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          __ARM_NR prefix T} getcpu(2) 2.6.19 getcwd(2) 2.2 get-
          dents(2)    2.0 getdents64(2)  2.4
          getdomainname(2)    2.2  T{ SPARC, SPARC64; available
          as osf_getdomainname(2)
          on Alpha since Linux 2.0 T} getdtablesize(2)    2.0  T{
          SPARC (removed in 2.6.26),
          available on Alpha as
          osf_getdtablesize(2) T} getegid(2)     1.0 gete-
          gid32(2)   2.4 geteuid(2)     1.0 geteuid32(2)   2.4 get-
          gid(2) 1.0 getgid32(2)    2.4 getgroups(2)   1.0 get-
          groups32(2) 2.4 gethostname(2) 2.0  T{ Alpha, was available
          SPARC up to Linux 2.6.26 T} getitimer(2)   1.0
          getpeername(2) 2.0  See notes on socketcall(2)
          getpagesize(2) 2.0  Not on x86 getpgid(2)     1.0 getp-
          grp(2)     1.0 getpid(2) 1.0 getppid(2)     1.0 getprior-
          ity(2) 1.0 getrandom(2)   3.17 getresgid(2)   2.2 getres-
          gid32(2) 2.4 getresuid(2)   2.2 getresuid32(2) 2.4 getr-
          limit(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) get-
          tid(2) 2.4.11 gettimeofday(2)     1.0 getuid(2) 1.0
          getuid32(2)    2.4 getunwind(2)   2.4.8     IA-64 only; dep-
          recated 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  T{ See
          chown(2) for
          version details T} 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 llistx-
          attr(2)  2.6; 2.4.18 lookup_dcookie(2)   2.6 lremovex-
          attr(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 mem-
          barrier(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

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          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 mun-
          lock(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  T{ Old variant of getrlimit(2)
          that used a different value
          for RLIM_INFINITY T} oldfstat(2)    1.0 oldlstat(2)    1.0
          oldolduname(2) 1.0 oldstat(2)     1.0
          oldumount(2)   2.4.116   T{ Name of the old umount(2)
          syscall on Alpha T} olduname(2)    1.0 open(2)   1.0
          open_by_handle_at(2)     2.6.39 open_tree(2)   5.2 ope-
          nat(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    T{ Was perf_counter_open() in
          2.6.31; renamed in 2.6.32 T} 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 pread64(2)          T{ Added
          as "pread" in 2.2;
          renamed "pread64" in 2.6 T} preadv(2) 2.6.30
          preadv2(2)     4.6 prlimit64(2)   2.6.36
          process_madvise(2)  5.10 process_vm_readv(2) 3.2
          process_vm_writev(2)     3.2 pselect6(2)    2.6.16
          ptrace(2) 1.0 pwrite64(2)         T{ Added as "pwrite" in
          renamed "pwrite64" in 2.6 T} pwritev(2)     2.6.30 pwri-
          tev2(2)    4.6 query_module(2)     2.2  Removed in 2.6 quo-
          tactl(2)    1.0 read(2)   1.0 readahead(2)   2.4.13 read-
          dir(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

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          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  T{ Name of
          on SPARC and SPARC64 T} 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  T{ Name of
          on SPARC and SPARC64 T} 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 sec-
          comp(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    T{ ARM OABI/EABI only (constant
          has __ARM_NR prefix) T} setdomainname(2)    1.0 setfs-
          gid(2)    1.2 setfsgid32(2)  2.4 setfsuid(2)    1.2 setf-
          suid32(2)  2.4 setgid(2) 1.0 setgid32(2)    2.4 set-
          groups(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  T{
          Alternative name for
          setpgid(2) on Alpha T} 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) settimeof-
          day(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) sigac-
          tion(2)   1.0 sigaltstack(2) 2.2 signal(2) 1.0 sig-
          nalfd(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

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          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 sset-
          mask(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 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  T{ Still available on ARM OABI
          and MIPS O32 ABI T} sysfs(2)  1.2 sysinfo(2)     1.0 sys-
          log(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 trun-
          cate64(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)   ARM
          OABI only usr32(2)   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  T{ Was "vm86";
          renamed in
          2.0.28/2.2 T} 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 System V IPC  calls  are  multi-
          plexed through ipc(2).

          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

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          in the standard kernel.

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

        System calls on removed ports
          Some system calls only ever existed on  Linux  architectures
          that have since been removed from the kernel:

          AVR32 (port removed in Linux 4.12)
               * pread(2)
               * pwrite(2)

          Blackfin (port removed in Linux 4.17)
               * bfin_spinlock(2) (added in Linux 2.6.22)
               * dma_memcpy(2) (added in Linux 2.6.22)
               * pread(2) (added in Linux 2.6.22)
               * pwrite(2) (added in Linux 2.6.22)
               * sram_alloc(2) (added in Linux 2.6.22)
               * sram_free(2) (added in Linux 2.6.22)

          Metag (port removed in Linux 4.17)
               * metag_get_tls(2) (add in Linux 3.9)
               * metag_set_fpu_flags(2) (add in Linux 3.9)
               * metag_set_tls(2) (add in Linux 3.9)
               * metag_setglobalbit(2) (add in Linux 3.9)

          Tile (port removed in Linux 4.17)
               * cmpxchg_badaddr(2) (added in Linux 2.6.36)

          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 platforms 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, cer-
          tain architectures (notably, longstanding  32-bit  architec-
          tures  such as i386) now have various groups of related sys-
          tem calls (e.g., truncate(2) and truncate64(2))  which  per-
          form  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

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          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 archi-
             tectures 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),
             getdents64(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

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     SYSCALLS(2)               (2020-12-21)                SYSCALLS(2)

             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() corre-
             sponding 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 archi-
             tecture 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  reg-
             isters  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 Exten-
             sion  register  on  low-cost  Alphas  in  order to access
             address space beyond first 27 bits.

          intro(2), syscall(2), unimplemented(2),  errno(3),  libc(7),

          This page is part of release 5.10  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

     Page 10                       Linux             (printed 5/22/22)