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       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 failure 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

   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 Linux 1.0 or earlier.

       •  Where  a  system call is marked "1.2" this means the system call probably appeared in a
          Linux  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
          Linux  1.3.x  kernel  version,  and  first  appeared in a stable kernel with Linux 2.0.
          (Development of the Linux 2.0 kernel was  initiated  from  a  branch  of  Linux  1.2.x,
          somewhere around Linux 1.2.10, via the Linux 1.3.x unstable kernel series.)

       •  Where  a  system call is marked "2.2" this means the system call probably appeared in a
          Linux 2.1.x kernel version, and first appeared in a stable  kernel  with  Linux  2.2.0.
          (Development of the Linux 2.2 kernel was initiated from a branch of kernel Linux 2.0.21
          via the Linux 2.1.x unstable kernel series.)

       •  Where a system call is marked "2.4" this means the system call probably appeared  in  a
          Linux  2.3.x  kernel  version,  and first appeared in a stable kernel with Linux 2.4.0.
          (Development of the Linux 2.4 kernel was initiated from a branch of Linux 2.2.8 via the
          Linux 2.3.x unstable kernel series.)

       •  Where  a  system call is marked "2.6" this means the system call probably appeared in a
          Linux 2.5.x kernel version, and first appeared in a stable  kernel  with  Linux  2.6.0.
          (Development  of  Linux  2.6  was initiated from a branch of Linux 2.4.15 via the Linux
          2.5.x unstable kernel series.)

       •  Starting with Linux 2.6.0, the development model changed,  and  new  system  calls  may
          appear  in  each Linux 2.6.x release.  In this case, the exact version number where the
          system call appeared is shown.  This convention continues with  the  Linux  3.x  kernel
          series,  which  followed  on  from Linux 2.6.39; and the Linux 4.x kernel series, which
          followed on from Linux 3.19; and the Linux 5.x kernel series, which  followed  on  from
          Linux 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  kernel
          series.   For  example  some  system  calls  that  appeared  in  Linux  2.6.x were also
          backported into a Linux 2.4.x release after Linux 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 Linux 5.14 (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           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           Deprecated (does nothing)
                                                 since 2.6
       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
       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_pwait2(2)             5.11
       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
       faccessat2(2)               5.8
       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

       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
       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
       landlock_add_rule(2)        5.13
       landlock_create_ruleset(2)  5.13
       landlock_restrict_self(2)   5.13
       lchown(2)                   1.0           See chown(2) for version
       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
       membarrier(2)               3.17
       memfd_create(2)             3.17
       memfd_secret(2)             5.14
       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
       perfmonctl(2)               2.4           IA-64 only; removed in 5.10
       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)                                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_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)                               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
       quotactl_fd(2)              5.14
       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
       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
       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
       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)                 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           Was "vm86"; renamed in
       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 multiplexed  through

       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 Linux 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 removed in Linux 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

       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 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),
          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 Linux 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
              returns  a  pair  of GID and effective GID via registers r0 and r20; it is provided
              instead of getgid(2) and getegid(2).

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

              is  a  variant  of  adjtimex(2)  that uses struct timeval32, for compatibility with

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

              is  used  for configuring the Host Address Extension register on low-cost Alphas in
              order to access address space beyond first 27 bits.


       ausyscall(1), intro(2), syscall(2), unimplemented(2), errno(3), libc(7), vdso(7)