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syscalls(2) System Calls Manualsyscalls(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, seeintro(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 functionchdir() 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 settingerrno appropriately after the system call has returned. (These are the same steps that are performed bysyscall(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 insyscall(2); when this happens, the wrapper function negates the returned error number (to make it positive), copies it toerrno, 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) andtruncate64(2), and the glibctruncate() 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, theKernel 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 Linux 1.2 kernel was initiated from a branch of Linux 1.0.6 via the Linux 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 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; and the Linux 6.x kernel series, which followed on from Linux 5.19. • 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 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 5.5accept(2) 2.0 See notes onsocketcall(2)accept4(2) 2.6.28access(2) 1.0acct(2) 1.0add_key(2) 2.6.10adjtimex(2) 1.0alarm(2) 1.0alloc_hugepages(2) 2.5.36 Removed in 2.5.44arc_gettls(2) 3.9 ARC onlyarc_settls(2) 3.9 ARC onlyarc_usr_cmpxchg(2) 4.9 ARC onlyarch_prctl(2) 2.6 x86_64, x86 since 4.12atomic_barrier(2) 2.6.34 m68k onlyatomic_cmpxchg_32(2) 2.6.34 m68k onlybdflush(2) 1.2 Deprecated (does nothing) since 2.6, removed in 5.15bind(2) 2.0 See notes onsocketcall(2)bpf(2) 3.18brk(2) 1.0breakpoint(2) 2.2 ARM OABI only, defined with__ARM_NRprefixcacheflush(2) 1.2 Not on x86capget(2) 2.2capset(2) 2.2chdir(2) 1.0chmod(2) 1.0chown(2) 2.2 Seechown(2) for version detailschown32(2) 2.4chroot(2) 1.0clock_adjtime(2) 2.6.39clock_getres(2) 2.6clock_gettime(2) 2.6clock_nanosleep(2) 2.6clock_settime(2) 2.6clone2(2) 2.4 IA-64 onlyclone(2) 1.0clone3(2) 5.3close(2) 1.0close_range(2) 5.9connect(2) 2.0 See notes onsocketcall(2)copy_file_range(2) 4.5creat(2) 1.0create_module(2) 1.0 Removed in 2.6delete_module(2) 1.0dup(2) 1.0dup2(2) 1.0dup3(2) 2.6.27epoll_create(2) 2.6epoll_create1(2) 2.6.27epoll_ctl(2) 2.6epoll_pwait(2) 2.6.19epoll_pwait2(2) 5.11epoll_wait(2) 2.6eventfd(2) 2.6.22eventfd2(2) 2.6.27execv(2) 2.0 SPARC/SPARC64 only, for compatibility with SunOSexecve(2) 1.0execveat(2) 3.19exit(2) 1.0exit_group(2) 2.6faccessat(2) 2.6.16faccessat2(2) 5.8fadvise64(2) 2.6fadvise64_64(2) 2.6fallocate(2) 2.6.23fanotify_init(2) 2.6.37fanotify_mark(2) 2.6.37fchdir(2) 1.0fchmod(2) 1.0fchmodat(2) 2.6.16fchown(2) 1.0fchown32(2) 2.4fchownat(2) 2.6.16fcntl(2) 1.0fcntl64(2) 2.4fdatasync(2) 2.0fgetxattr(2) 2.6; 2.4.18finit_module(2) 3.8flistxattr(2) 2.6; 2.4.18flock(2) 2.0fork(2) 1.0free_hugepages(2) 2.5.36 Removed in 2.5.44fremovexattr(2) 2.6; 2.4.18fsconfig(2) 5.2fsetxattr(2) 2.6; 2.4.18fsmount(2) 5.2fsopen(2) 5.2fspick(2) 5.2fstat(2) 1.0fstat64(2) 2.4fstatat64(2) 2.6.16fstatfs(2) 1.0fstatfs64(2) 2.6fsync(2) 1.0ftruncate(2) 1.0ftruncate64(2) 2.4futex(2) 2.6futimesat(2) 2.6.16get_kernel_syms(2) 1.0 Removed in 2.6get_mempolicy(2) 2.6.6get_robust_list(2) 2.6.17get_thread_area(2) 2.6get_tls(2) 4.15 ARM OABI only, has__ARM_NR prefixgetcpu(2) 2.6.19getcwd(2) 2.2getdents(2) 2.0getdents64(2) 2.4getdomainname(2) 2.2 SPARC, SPARC64; available asosf_getdomainname(2) on Alpha since Linux 2.0getdtablesize(2) 2.0 SPARC (removed in 2.6.26), available on Alpha asosf_getdtablesize(2)getegid(2) 1.0getegid32(2) 2.4geteuid(2) 1.0geteuid32(2) 2.4getgid(2) 1.0getgid32(2) 2.4getgroups(2) 1.0getgroups32(2) 2.4gethostname(2) 2.0 Alpha, was available on SPARC up to Linux 2.6.26getitimer(2) 1.0getpeername(2) 2.0 See notes onsocketcall(2)getpagesize(2) 2.0 Alpha, SPARC/SPARC64 onlygetpgid(2) 1.0getpgrp(2) 1.0getpid(2) 1.0getppid(2) 1.0getpriority(2) 1.0getrandom(2) 3.17getresgid(2) 2.2getresgid32(2) 2.4getresuid(2) 2.2getresuid32(2) 2.4getrlimit(2) 1.0getrusage(2) 1.0getsid(2) 2.0getsockname(2) 2.0 See notes onsocketcall(2)getsockopt(2) 2.0 See notes onsocketcall(2)gettid(2) 2.4.11gettimeofday(2) 1.0getuid(2) 1.0getuid32(2) 2.4getunwind(2) 2.4.8 IA-64 only; deprecatedgetxattr(2) 2.6; 2.4.18getxgid(2) 2.0 Alpha only; see NOTESgetxpid(2) 2.0 Alpha only; see NOTESgetxuid(2) 2.0 Alpha only; see NOTESinit_module(2) 1.0inotify_add_watch(2) 2.6.13inotify_init(2) 2.6.13inotify_init1(2) 2.6.27inotify_rm_watch(2) 2.6.13io_cancel(2) 2.6io_destroy(2) 2.6io_getevents(2) 2.6io_pgetevents(2) 4.18io_setup(2) 2.6io_submit(2) 2.6io_uring_enter(2) 5.1io_uring_register(2) 5.1io_uring_setup(2) 5.1ioctl(2) 1.0ioperm(2) 1.0iopl(2) 1.0ioprio_get(2) 2.6.13ioprio_set(2) 2.6.13ipc(2) 1.0kcmp(2) 3.5kern_features(2) 3.7 SPARC64 onlykexec_file_load(2) 3.17kexec_load(2) 2.6.13keyctl(2) 2.6.10kill(2) 1.0landlock_add_rule(2) 5.13landlock_create_ruleset(2) 5.13landlock_restrict_self(2) 5.13lchown(2) 1.0 Seechown(2) for version detailslchown32(2) 2.4lgetxattr(2) 2.6; 2.4.18link(2) 1.0linkat(2) 2.6.16listen(2) 2.0 See notes onsocketcall(2)listxattr(2) 2.6; 2.4.18llistxattr(2) 2.6; 2.4.18lookup_dcookie(2) 2.6lremovexattr(2) 2.6; 2.4.18lseek(2) 1.0lsetxattr(2) 2.6; 2.4.18lstat(2) 1.0lstat64(2) 2.4madvise(2) 2.4mbind(2) 2.6.6memory_ordering(2) 2.2 SPARC64 onlymembarrier(2) 3.17memfd_create(2) 3.17memfd_secret(2) 5.14migrate_pages(2) 2.6.16mincore(2) 2.4mkdir(2) 1.0mkdirat(2) 2.6.16mknod(2) 1.0mknodat(2) 2.6.16mlock(2) 2.0mlock2(2) 4.4mlockall(2) 2.0mmap(2) 1.0mmap2(2) 2.4modify_ldt(2) 1.0mount(2) 1.0move_mount(2) 5.2move_pages(2) 2.6.18mprotect(2) 1.0mq_getsetattr(2) 2.6.6mq_notify(2) 2.6.6mq_open(2) 2.6.6mq_timedreceive(2) 2.6.6mq_timedsend(2) 2.6.6mq_unlink(2) 2.6.6mremap(2) 2.0msgctl(2) 2.0 See notes onipc(2)msgget(2) 2.0 See notes onipc(2)msgrcv(2) 2.0 See notes onipc(2)msgsnd(2) 2.0 See notes onipc(2)msync(2) 2.0munlock(2) 2.0munlockall(2) 2.0munmap(2) 1.0name_to_handle_at(2) 2.6.39nanosleep(2) 2.0newfstatat(2) 2.6.16 Seestat(2)nfsservctl(2) 2.2 Removed in 3.1nice(2) 1.0old_adjtimex(2) 2.0 Alpha only; see NOTESold_getrlimit(2) 2.4 Old variant ofgetrlimit(2) that used a different value forRLIM_INFINITYoldfstat(2) 1.0oldlstat(2) 1.0oldolduname(2) 1.0oldstat(2) 1.0oldumount(2) 2.4.116 Name of the oldumount(2) syscall on Alphaolduname(2) 1.0open(2) 1.0open_by_handle_at(2) 2.6.39open_tree(2) 5.2openat(2) 2.6.16openat2(2) 5.6or1k_atomic(2) 3.1 OpenRISC 1000 onlypause(2) 1.0pciconfig_iobase(2) 2.2.15; 2.4 Not on x86pciconfig_read(2) 2.0.26; 2.2 Not on x86pciconfig_write(2) 2.0.26; 2.2 Not on x86perf_event_open(2) 2.6.31 Was perf_counter_open() in 2.6.31; renamed in 2.6.32personality(2) 1.2perfctr(2) 2.2 SPARC only; removed in 2.6.34perfmonctl(2) 2.4 IA-64 only; removed in 5.10pidfd_getfd(2) 5.6pidfd_send_signal(2) 5.1pidfd_open(2) 5.3pipe(2) 1.0pipe2(2) 2.6.27pivot_root(2) 2.4pkey_alloc(2) 4.8pkey_free(2) 4.8pkey_mprotect(2) 4.8poll(2) 2.0.36; 2.2ppoll(2) 2.6.16prctl(2) 2.2pread64(2) Added as "pread" in 2.2; renamed "pread64" in 2.6preadv(2) 2.6.30preadv2(2) 4.6prlimit64(2) 2.6.36process_madvise(2) 5.10process_vm_readv(2) 3.2process_vm_writev(2) 3.2pselect6(2) 2.6.16ptrace(2) 1.0pwrite64(2) Added as "pwrite" in 2.2; renamed "pwrite64" in 2.6pwritev(2) 2.6.30pwritev2(2) 4.6query_module(2) 2.2 Removed in 2.6quotactl(2) 1.0quotactl_fd(2) 5.14read(2) 1.0readahead(2) 2.4.13readdir(2) 1.0readlink(2) 1.0readlinkat(2) 2.6.16readv(2) 2.0reboot(2) 1.0recv(2) 2.0 See notes onsocketcall(2)recvfrom(2) 2.0 See notes onsocketcall(2)recvmsg(2) 2.0 See notes onsocketcall(2)recvmmsg(2) 2.6.33remap_file_pages(2) 2.6 Deprecated since 3.16removexattr(2) 2.6; 2.4.18rename(2) 1.0renameat(2) 2.6.16renameat2(2) 3.15request_key(2) 2.6.10restart_syscall(2) 2.6riscv_flush_icache(2) 4.15 RISC-V onlyrmdir(2) 1.0rseq(2) 4.18rt_sigaction(2) 2.2rt_sigpending(2) 2.2rt_sigprocmask(2) 2.2rt_sigqueueinfo(2) 2.2rt_sigreturn(2) 2.2rt_sigsuspend(2) 2.2rt_sigtimedwait(2) 2.2rt_tgsigqueueinfo(2) 2.6.31rtas(2) 2.6.2 PowerPC/PowerPC64 onlys390_runtime_instr(2) 3.7 s390 onlys390_pci_mmio_read(2) 3.19 s390 onlys390_pci_mmio_write(2) 3.19 s390 onlys390_sthyi(2) 4.15 s390 onlys390_guarded_storage(2) 4.12 s390 onlysched_get_affinity(2) 2.6 Name ofsched_getaffinity(2) on SPARC and SPARC64sched_get_priority_max(2) 2.0sched_get_priority_min(2) 2.0sched_getaffinity(2) 2.6sched_getattr(2) 3.14sched_getparam(2) 2.0sched_getscheduler(2) 2.0sched_rr_get_interval(2) 2.0sched_set_affinity(2) 2.6 Name ofsched_setaffinity(2) on SPARC and SPARC64sched_setaffinity(2) 2.6sched_setattr(2) 3.14sched_setparam(2) 2.0sched_setscheduler(2) 2.0sched_yield(2) 2.0seccomp(2) 3.17select(2) 1.0semctl(2) 2.0 See notes onipc(2)semget(2) 2.0 See notes onipc(2)semop(2) 2.0 See notes onipc(2)semtimedop(2) 2.6; 2.4.22send(2) 2.0 See notes onsocketcall(2)sendfile(2) 2.2sendfile64(2) 2.6; 2.4.19sendmmsg(2) 3.0sendmsg(2) 2.0 See notes onsocketcall(2)sendto(2) 2.0 See notes onsocketcall(2)set_mempolicy(2) 2.6.6set_robust_list(2) 2.6.17set_thread_area(2) 2.6set_tid_address(2) 2.6set_tls(2) 2.6.11 ARM OABI/EABI only (constant has__ARM_NR prefix)setdomainname(2) 1.0setfsgid(2) 1.2setfsgid32(2) 2.4setfsuid(2) 1.2setfsuid32(2) 2.4setgid(2) 1.0setgid32(2) 2.4setgroups(2) 1.0setgroups32(2) 2.4sethae(2) 2.0 Alpha only; see NOTESsethostname(2) 1.0setitimer(2) 1.0setns(2) 3.0setpgid(2) 1.0setpgrp(2) 2.0 Alternative name forsetpgid(2) on Alphasetpriority(2) 1.0setregid(2) 1.0setregid32(2) 2.4setresgid(2) 2.2setresgid32(2) 2.4setresuid(2) 2.2setresuid32(2) 2.4setreuid(2) 1.0setreuid32(2) 2.4setrlimit(2) 1.0setsid(2) 1.0setsockopt(2) 2.0 See notes onsocketcall(2)settimeofday(2) 1.0setuid(2) 1.0setuid32(2) 2.4setup(2) 1.0 Removed in 2.2setxattr(2) 2.6; 2.4.18sgetmask(2) 1.0shmat(2) 2.0 See notes onipc(2)shmctl(2) 2.0 See notes onipc(2)shmdt(2) 2.0 See notes onipc(2)shmget(2) 2.0 See notes onipc(2)shutdown(2) 2.0 See notes onsocketcall(2)sigaction(2) 1.0sigaltstack(2) 2.2signal(2) 1.0signalfd(2) 2.6.22signalfd4(2) 2.6.27sigpending(2) 1.0sigprocmask(2) 1.0sigreturn(2) 1.0sigsuspend(2) 1.0socket(2) 2.0 See notes onsocketcall(2)socketcall(2) 1.0socketpair(2) 2.0 See notes onsocketcall(2)spill(2) 2.6.13 Xtensa onlysplice(2) 2.6.17spu_create(2) 2.6.16 PowerPC/PowerPC64 onlyspu_run(2) 2.6.16 PowerPC/PowerPC64 onlyssetmask(2) 1.0stat(2) 1.0stat64(2) 2.4statfs(2) 1.0statfs64(2) 2.6statx(2) 4.11stime(2) 1.0subpage_prot(2) 2.6.25 PowerPC/PowerPC64 onlyswapcontext(2) 2.6.3 PowerPC/PowerPC64 onlyswitch_endian(2) 4.1 PowerPC64 onlyswapoff(2) 1.0swapon(2) 1.0symlink(2) 1.0symlinkat(2) 2.6.16sync(2) 1.0sync_file_range(2) 2.6.17sync_file_range2(2) 2.6.22syncfs(2) 2.6.39sys_debug_setcontext(2) 2.6.11 PowerPC onlysyscall(2) 1.0 Still available on ARM OABI and MIPS O32 ABIsysfs(2) 1.2sysinfo(2) 1.0syslog(2) 1.0sysmips(2) 2.6.0 MIPS onlytee(2) 2.6.17tgkill(2) 2.6time(2) 1.0timer_create(2) 2.6timer_delete(2) 2.6timer_getoverrun(2) 2.6timer_gettime(2) 2.6timer_settime(2) 2.6timerfd_create(2) 2.6.25timerfd_gettime(2) 2.6.25timerfd_settime(2) 2.6.25times(2) 1.0tkill(2) 2.6; 2.4.22truncate(2) 1.0truncate64(2) 2.4ugetrlimit(2) 2.4umask(2) 1.0umount(2) 1.0umount2(2) 2.2uname(2) 1.0unlink(2) 1.0unlinkat(2) 2.6.16unshare(2) 2.6.16uselib(2) 1.0ustat(2) 1.0userfaultfd(2) 4.3usr26(2) 2.4.8.1 ARM OABI onlyusr32(2) 2.4.8.1 ARM OABI onlyutime(2) 1.0utimensat(2) 2.6.22utimes(2) 2.2utrap_install(2) 2.2 SPARC64 onlyvfork(2) 2.2vhangup(2) 1.0vm86old(2) 1.0 Was "vm86"; renamed in 2.0.28/2.2vm86(2) 2.0.28; 2.2vmsplice(2) 2.6.17wait4(2) 1.0waitid(2) 2.6.10waitpid(2) 1.0write(2) 1.0writev(2) 2.0xtensa(2) 2.6.13 Xtensa only On many platforms, including x86-32, socket calls are all multiplexed (via glibc wrapper functions) throughsocketcall(2) and similarly System V IPC calls are multiplexed throughipc(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), andvserver(2) (see alsounimplemented(2)). However,ftime(3),profil(3), andulimit(3) exist as library routines. The slot forphys(2) is in use since Linux 2.1.116 forumount(2);phys(2) will never be implemented. Thegetpmsg(2) andputpmsg(2) calls are for kernels patched to support STREAMS, and may never be in the standard kernel. There was brieflyset_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 routinesys_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) andtruncate64(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 system calls that exist in multiple versions are the following: • By now there are three different versions ofstat(2):sys_stat() (slot__NR_oldstat),sys_newstat() (slot__NR_stat), andsys_stat64() (slot__NR_stat64), with the last being the most current. A similar story applies forlstat(2) andfstat(2). • Similarly, the defines__NR_oldolduname,__NR_olduname, and__NR_uname refer to the routinessys_olduname(),sys_uname(), andsys_newuname(). • In Linux 2.0, a new version ofvm86(2) appeared, with the old and the new kernel routines being namedsys_vm86old() andsys_vm86(). • In Linux 2.4, a new version ofgetrlimit(2) appeared, with the old and the new kernel routines being namedsys_old_getrlimit() (slot__NR_getrlimit) andsys_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. • Thert_sig* calls were added in Linux 2.2 to support the addition of real-time signals (seesignal(7)). These system calls supersede the older system calls of the same name without the "rt_" prefix. • Theselect(2) andmmap(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 havesys_select() andsys_mmap() corresponding to__NR_select and__NR_mmap, on i386 one findsold_select() andold_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 tosys_select() and similarly__NR_mmap2. s390x is the only 64-bit architecture that hasold_mmap().Architecture-specific details: Alphagetxgid(2) returns a pair of GID and effective GID via registersr0 andr20; it is provided instead ofgetgid(2) andgetegid(2).getxpid(2) returns a pair of PID and parent PID via registersr0andr20; it is provided instead ofgetpid(2) andgetppid(2).old_adjtimex(2) is a variant ofadjtimex(2) that usesstruct timeval32, for compatibility with OSF/1.getxuid(2) returns a pair of GID and effective GID via registersr0 andr20; it is provided instead ofgetuid(2) andgeteuid(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.
intro(2),syscall(2),unimplemented(2),errno(3),libc(7),vdso(7),ausyscall(8)
This page is part of theman-pages (Linux kernel and C library user-space interface documentation) project. Information about the project can be found at ⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report for this manual page, see ⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩. This page was obtained from the tarball man-pages-6.15.tar.gz fetched from ⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on 2025-08-11. If you discover any rendering problems in this HTML version of the page, or you believe there is a better or more up- to-date source for the page, or you have corrections or improvements to the information in this COLOPHON (which isnot part of the original manual page), send a mail to man-pages@man7.orgLinux man-pages 6.15 2025-05-17syscalls(2)Pages that refer to this page:strace(1), intro(2), syscall(2), unimplemented(2), stapprobes(3stap), libc(7), man-pages(7), vdso(7)
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