syscalls

SYSCALLS(2)                Linux Programmer's Manual               SYSCALLS(2)



NAME
       syscalls - Linux system calls

SYNOPSIS
       Linux system calls.

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

   System calls and library wrapper functions
       System calls are generally not invoked directly, but rather via wrapper
       functions in glibc (or perhaps some other library).  For details of
       direct invocation of a system call, see intro(2).  Often, but not
       always, the name of the wrapper function is the same as the name of the
       system call that it invokes.  For example, glibc contains a function
       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 wrapper.

       Sometimes, however, the wrapper function does some extra work before
       invoking the system call.  For example, nowadays there are (for reasons
       described below) two related system calls, truncate(2) and
       truncate64(2), and the glibc truncate() wrapper function checks which
       of those system calls are provided by the kernel and determines which
       should be employed.

   System call list
       Below is a list of 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
          probably appeared in a 1.1.x kernel version, and first appeared in a
          stable kernel with 1.2.  (Development of the 1.2 kernel was
          initiated from a branch of kernel 1.0.6 via the 1.1.x unstable
          kernel series.)

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

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

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

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

       *  Starting with kernel 2.6.0, the development model changed, and new
          system calls may appear in each 2.6.x release.  In this case, the
          exact version number where the system call appeared is shown.  This
          convention continues with the 3.x kernel series, which followed on
          from kernel 2.6.39, and the 4.x kernel series, which followed on
          from kernel 3.19.

       *  In some cases, a system call was added to a stable kernel series
          after it branched from the previous stable kernel series, and then
          backported into the earlier stable kernel series.  For example some
          system calls that appeared in 2.6.x were also backported into a
          2.4.x release after 2.4.15.  When this is so, the version where the
          system call appeared in both of the major kernel series is listed.

       The list of system calls that are available as at kernel 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 since Linux 2.0 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
       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_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
       System V IPC calls are multiplexed 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 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.

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
       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, 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 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
          register 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 5.04 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                             2019-10-10                       SYSCALLS(2)