syscalls(2)

okay so bestie, you've stumbled into syscalls(2) from the System Calls Manual and honestly? this is the blueprint. the origin story. the one that explains why literally every other syscall manpage exists. 🦋

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💖 NAME 💖

syscalls — Linux system calls

that's it. that's the name. short, sweet, iconic. 💅

✨ SYNOPSIS ✨

Linux system calls.

like… yes. the synopsis is the thing itself. minimalist queen behavior, no notes. 👑

🌸 DESCRIPTION 🌸

bestie. listen. the system call is the fundamental interface between an application and the Linux kernel. that's not me being dramatic, that's literally the words. it's the doorway. the connection. the way your little program gets to whisper to the kernel and have the kernel actually do something about it. 🫶

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🎀 System calls and library wrapper functions 🎀

okay so here's the tea: syscalls are generally not invoked directly — you go through wrapper functions in glibc (or maybe some other library, we don't gatekeep). wanna know about direct invocation? that's a whole other vibe, go read intro(2). 📖

often — but not always, ok don't @ me — the wrapper function's name is exactly the same as the name of the system call it invokes. example: glibc has a function chdir() which invokes the underlying "chdir" system call. same name, different layer, so cute. ✨

and often the glibc wrapper is thin — like, it does barely any 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. (fun fact: these are the exact same steps performed by syscall(2), which you can use to invoke system calls that have no wrapper function at all. icon behavior.) 🎀

okay this part matters so pay attention bestie: 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 that 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. that's the failure pipeline. that's the lore. 😭

sometimes though, the wrapper function does extra work before invoking the system call. example: nowadays there are (for reasons described below, we'll get there) 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. it's a whole matchmaking situation. 💅

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🌈 System call list 🌈

below is a list of the Linux system calls. in that list, the Kernel column tells you 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, bestie, because the version-column lore is REAL:

• where no kernel version is indicated, the system call appeared in Linux 1.0 or earlier. ancient. vintage. the elders. 🧚
• 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. so many series. so many follow-ons. the lineage is unbroken. 👑
• 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. double-dipping, but make it versioning. 💅

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and now for the main event, 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: 🌟

okay so the big list continues and it's giving encyclopedia energy 💅 every syscall, every kernel debut, every little footnote — no cap, it's all here.

• _llseek(2) — kernel 1.2
• _newselect(2) — kernel 2.0
• _sysctl(2) — kernel 2.0 — Removed in 5.5 💀
• accept(2) — kernel 2.0 — See notes on socketcall(2)
• accept4(2) — kernel 2.6.28
• access(2) — kernel 1.0
• acct(2) — kernel 1.0
• add_key(2) — kernel 2.6.10
• adjtimex(2) — kernel 1.0
• alarm(2) — kernel 1.0
• alloc_hugepages(2) — kernel 2.5.36 — Removed in 2.5.44 😭
• arc_gettls(2) — kernel 3.9 — ARC only
• arc_settls(2) — kernel 3.9 — ARC only
• arc_usr_cmpxchg(2) — kernel 4.9 — ARC only
• arch_prctl(2) — kernel 2.6 — x86_64, x86 since 4.12
• atomic_barrier(2) — kernel 2.6.34 — m68k only
• atomic_cmpxchg_32(2) — kernel 2.6.34 — m68k only
• bdflush(2) — kernel 1.2 — Deprecated (does nothing) since 2.6, removed in 5.15
• bind(2) — kernel 2.0 — See notes on socketcall(2)
• bpf(2) — kernel 3.18
• brk(2) — kernel 1.0
• breakpoint(2) — kernel 2.2 — ARM OABI only, defined with __ARM_NR prefix
• cacheflush(2) — kernel 1.2 — Not on x86
• capget(2) — kernel 2.2
• capset(2) — kernel 2.2
• chdir(2) — kernel 1.0
• chmod(2) — kernel 1.0
• chown(2) — kernel 2.2 — See chown(2) for version details
• chown32(2) — kernel 2.4
• chroot(2) — kernel 1.0
• clock_adjtime(2) — kernel 2.6.39
• clock_getres(2) — kernel 2.6
• clock_gettime(2) — kernel 2.6
• clock_nanosleep(2) — kernel 2.6
• clock_settime(2) — kernel 2.6
• clone2(2) — kernel 2.4 — IA-64 only
• clone(2) — kernel 1.0
• clone3(2) — kernel 5.3
• close(2) — kernel 1.0
• close_range(2) — kernel 5.9
• connect(2) — kernel 2.0 — See notes on socketcall(2)
• copy_file_range(2) — kernel 4.5
• creat(2) — kernel 1.0
• create_module(2) — kernel 1.0 — Removed in 2.6
• delete_module(2) — kernel 1.0
• dup(2) — kernel 1.0
• dup2(2) — kernel 1.0
• dup3(2) — kernel 2.6.27
• epoll_create(2) — kernel 2.6
• epoll_create1(2) — kernel 2.6.27
• epoll_ctl(2) — kernel 2.6
• epoll_pwait(2) — kernel 2.6.19
• epoll_pwait2(2) — kernel 5.11
• epoll_wait(2) — kernel 2.6
• eventfd(2) — kernel 2.6.22
• eventfd2(2) — kernel 2.6.27
• execv(2) — kernel 2.0 — SPARC/SPARC64 only, for compatibility with SunOS
• execve(2) — kernel 1.0
• execveat(2) — kernel 3.19
• exit(2) — kernel 1.0
• exit_group(2) — kernel 2.6
• faccessat(2) — kernel 2.6.16
• faccessat2(2) — kernel 5.8
• fadvise64(2) — kernel 2.6
• fadvise64_64(2) — kernel 2.6
• fallocate(2) — kernel 2.6.23
• fanotify_init(2) — kernel 2.6.37
• fanotify_mark(2) — kernel 2.6.37
• fchdir(2) — kernel 1.0
• fchmod(2) — kernel 1.0
• fchmodat(2) — kernel 2.6.16
• fchown(2) — kernel 1.0
• fchown32(2) — kernel 2.4
• fchownat(2) — kernel 2.6.16
• fcntl(2) — kernel 1.0
• fcntl64(2) — kernel 2.4
• fdatasync(2) — kernel 2.0
• fgetxattr(2) — kernel 2.6; 2.4.18
• finit_module(2) — kernel 3.8
• flistxattr(2) — kernel 2.6; 2.4.18
• flock(2) — kernel 2.0
• fork(2) — kernel 1.0
• free_hugepages(2) — kernel 2.5.36 — Removed in 2.5.44
• fremovexattr(2) — kernel 2.6; 2.4.18
• fsconfig(2) — kernel 5.2
• fsetxattr(2) — kernel 2.6; 2.4.18
• fsmount(2) — kernel 5.2
• fsopen(2) — kernel 5.2
• fspick(2) — kernel 5.2
• fstat(2) — kernel 1.0
• fstat64(2) — kernel 2.4
• fstatat64(2) — kernel 2.6.16
• fstatfs(2) — kernel 1.0
• fstatfs64(2) — kernel 2.6
• fsync(2) — kernel 1.0
• ftruncate(2) — kernel 1.0
• ftruncate64(2) — kernel 2.4
• futex(2) — kernel 2.6
• futimesat(2) — kernel 2.6.16
• get_kernel_syms(2) — kernel 1.0 — Removed in 2.6
• get_mempolicy(2) — kernel 2.6.6
• get_robust_list(2) — kernel 2.6.17
• get_thread_area(2) — kernel 2.6
• get_tls(2) — kernel 4.15 — ARM OABI only, has __ARM_NR prefix
• getcpu(2) — kernel 2.6.19
• getcwd(2) — kernel 2.2
• getdents(2) — kernel 2.0
• getdents64(2) — kernel 2.4
• getdomainname(2) — kernel 2.2 — SPARC, SPARC64; available as osf_getdomainname(2) on Alpha since Linux 2.0
• getdtablesize(2) — kernel 2.0 — SPARC (removed in 2.6.26), available on Alpha as osf_getdtablesize(2)
• getegid(2) — kernel 1.0
• getegid32(2) — kernel 2.4
• geteuid(2) — kernel 1.0
• geteuid32(2) — kernel 2.4
• getgid(2) — kernel 1.0
• getgid32(2) — kernel 2.4
• getgroups(2) — kernel 1.0
• getgroups32(2) — kernel 2.4
• gethostname(2) — kernel 2.0 — Alpha, was available on SPARC up to Linux 2.6.26
• getitimer(2) — kernel 1.0
• getpeername(2) — kernel 2.0 — See notes on socketcall(2)
• getpagesize(2) — kernel 2.0 — Alpha, SPARC/SPARC64 only
• getpgid(2) — kernel 1.0
• getpgrp(2) — kernel 1.0
• getpid(2) — kernel 1.0
• getppid(2) — kernel 1.0
• getpriority(2) — kernel 1.0
• getrandom(2) — kernel 3.17
• getresgid(2) — kernel 2.2
• getresgid32(2) — kernel 2.4
• getresuid(2) — kernel 2.2
• getresuid32(2) — kernel 2.4
• getrlimit(2) — kernel 1.0
• getrusage(2) — kernel 1.0
• getsid(2) — kernel 2.0
• getsockname(2) — kernel 2.0 — See notes on socketcall(2)
• getsockopt(2) — kernel 2.0 — See notes on socketcall(2)
• gettid(2) — kernel 2.4.11
• gettimeofday(2) — kernel 1.0
• getuid(2) — kernel 1.0
• getuid32(2) — kernel 2.4
• getunwind(2) — kernel 2.4.8 — IA-64 only; deprecated
• getxattr(2) — kernel 2.6; 2.4.18
• getxgid(2) — kernel 2.0 — Alpha only; see NOTES
• getxpid(2) — kernel 2.0 — Alpha only; see NOTES
• getxuid(2) — kernel 2.0 — Alpha only; see NOTES
• init_module(2) — kernel 1.0
• inotify_add_watch(2) — kernel 2.6.13
• inotify_init(2) — kernel 2.6.13
• inotify_init1(2) — kernel 2.6.27
• inotify_rm_watch(2) — kernel 2.6.13
• io_cancel(2) — kernel 2.6
• io_destroy(2) — kernel 2.6
• io_getevents(2) — kernel 2.6
• io_pgetevents(2) — kernel 4.18
• io_setup(2) — kernel 2.6
• io_submit(2) — kernel 2.6
• io_uring_enter(2) — kernel 5.1
• io_uring_register(2) — kernel 5.1
• io_uring_setup(2) — kernel 5.1
• ioctl(2) — kernel 1.0
• ioperm(2) — kernel 1.0
• iopl(2) — kernel 1.0
• ioprio_get(2) — kernel 2.6.13
• ioprio_set(2) — kernel 2.6.13
• ipc(2) — kernel 1.0
• kcmp(2) — kernel 3.5
• kern_features(2) — kernel 3.7 — SPARC64 only
• kexec_file_load(2) — kernel 3.17
• kexec_load(2) — kernel 2.6.13
• keyctl(2) — kernel 2.6.10
• kill(2) — kernel 1.0
• landlock_add_rule(2) — kernel 5.13
• landlock_create_ruleset(2) — kernel 5.13
• landlock_restrict_self(2) — kernel 5.13
• lchown(2) — kernel 1.0 — See chown(2) for version details
• lchown32(2) — kernel 2.4
• lgetxattr(2) — kernel 2.6; 2.4.18
• link(2) — kernel 1.0
• linkat(2) — kernel 2.6.16
• listen(2) — kernel 2.0 — See notes on socketcall(2)
• listxattr(2) — kernel 2.6; 2.4.18
• llistxattr(2) — kernel 2.6; 2.4.18
• lookup_dcookie(2) — kernel 2.6
• lremovexattr(2) — kernel 2.6; 2.4.18
• lseek(2) — kernel 1.0
• lsetxattr(2) — kernel 2.6; 2.4.18
• lstat(2) — kernel 1.0
• lstat64(2) — kernel 2.4
• madvise(2) — kernel 2.4
• mbind(2) — kernel 2.6.6
• memory_ordering(2) — kernel 2.2 — SPARC64 only
• membarrier(2) — kernel 3.17
• memfd_create(2) — kernel 3.17
• memfd_secret(2) — kernel 5.14
• migrate_pages(2) — kernel 2.6.16
• mincore(2) — kernel 2.4
• mkdir(2) — kernel 1.0
• mkdirat(2) — kernel 2.6.16
• mknod(2) — kernel 1.0
• mknodat(2) — kernel 2.6.16
• mlock(2) — kernel 2.0
• mlock2(2) — kernel 4.4
• mlockall(2) — kernel 2.0
• mmap(2) — kernel 1.0
• mmap2(2) — kernel 2.4
• modify_ldt(2) — kernel 1.0
• mount(2) — kernel 1.0
• move_mount(2) — kernel 5.2
• move_pages(2) — kernel 2.6.18
• mprotect(2) — kernel 1.0
• mq_getsetattr(2) — kernel 2.6.6
• mq_notify(2) — kernel 2.6.6
• mq_open(2) — kernel 2.6.6
• mq_timedreceive(2) — kernel 2.6.6
• mq_timedsend(2) — kernel 2.6.6
• mq_unlink(2) — kernel 2.6.6
• mremap(2) — kernel 2.0
• msgctl(2) — kernel 2.0 — See notes on ipc(2)
• msgget(2) — kernel 2.0 — See notes on ipc(2)
• msgrcv(2) — kernel 2.0 — See notes on ipc(2)
• msgsnd(2) — kernel 2.0 — See notes on ipc(2)
• msync(2) — kernel 2.0
• munlock(2) — kernel 2.0
• munlockall(2) — kernel 2.0
• munmap(2) — kernel 1.0
• name_to_handle_at(2) — kernel 2.6.39
• nanosleep(2) — kernel 2.0
• newfstatat(2) — kernel 2.6.16 — See stat(2)
• nfsservctl(2) — kernel 2.2 — Removed in 3.1
• nice(2) — kernel 1.0
• old_adjtimex(2) — kernel 2.0 — Alpha only; see NOTES
• old_getrlimit(2) — kernel 2.4 — Old variant of getrlimit(2) that used a different value for RLIM_INFINITY
• oldfstat(2) — kernel 1.0
• oldlstat(2) — kernel 1.0
• oldolduname(2) — kernel 1.0
• oldstat(2) — kernel 1.0
• oldumount(2) — 2.4.116 · this is just the name the old umount(2) syscall goes by 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, bestie 🌸
• pause(2) — 1.0
• pciconfig_iobase(2) — 2.2.15; 2.4 · literally not on x86
• pciconfig_read(2) — 2.0.26; 2.2 · also not on x86
• pciconfig_write(2) — 2.0.26; 2.2 · yeah, not on x86 either 🫠
• perf_event_open(2) — 2.6.31 · it was called perf_counter_open() back in 2.6.31, then got renamed in 2.6.32
• personality(2) — 1.2
• perfctr(2) — 2.2 · SPARC only, and it got removed in 2.6.34 💀
• 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) — no version column for this one · it was added as pread in 2.2 and got 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) — no version column here either · 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, rip 🙈
• 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 the notes on socketcall(2)
• recvfrom(2) — 2.0 · see the notes on socketcall(2)
• recvmsg(2) — 2.0 · see the notes on socketcall(2)
• recvmmsg(2) — 2.6.33
• remap_file_pages(2) — 2.6 · deprecated since 3.16, so maybe don't ✨
• 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 · this is the name sched_getaffinity(2) goes by 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 · and this is the name sched_setaffinity(2) goes by 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 the notes on ipc(2)
• semget(2) — 2.0 · see the notes on ipc(2)
• semop(2) — 2.0 · see the notes on ipc(2)
• semtimedop(2) — 2.6; 2.4.22
• send(2) — 2.0 · see the notes on socketcall(2)
• sendfile(2) — 2.2
• sendfile64(2) — 2.6; 2.4.19
• sendmmsg(2) — 3.0
• sendmsg(2) — 2.0 · see the notes on socketcall(2)
• sendto(2) — 2.0 · see the 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 (the constant has the __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, peep the NOTES for this one
• sethostname(2) — 1.0
• setitimer(2) — 1.0
• setns(2) — 3.0
• setpgid(2) — 1.0
• setpgrp(2) — 2.0 · an 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 the 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 the notes on ipc(2)
• shmctl(2) — 2.0 · see the notes on ipc(2)
• shmdt(2) — 2.0 · see the notes on ipc(2)
• shmget(2) — 2.0 · see the notes on ipc(2)
• shutdown(2) — 2.0 · see the 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 the notes on socketcall(2)
• socketcall(2) — 1.0
• socketpair(2) — 2.0 · see the 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, iconic behavior ✨
• 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 · this one was just vm86 and got 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

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okay so one last thing before we move on, bestie, because it's important and it's giving "plot twist" 💅

On a bunch of platforms — x86-32 included — all the socket calls are multiplexed (through glibc wrapper functions, no less) via socketcall(2). And in the same way, the System V IPC calls are multiplexed through ipc(2). So when you see "see the notes on socketcall(2)" or "see the notes on ipc(2)" up there, that's the whole tea 🫖✨

okay so real talk: the kernel's system call table has slots reserved for a whole bunch of calls that just... never showed up. They're in the table, bestie, but they 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)
• vserver(2)

(also see unimplemented(2) — it's giving "the graveyard, but make it documentation" 🪦)

BUT plot twist: ftime(3), profil(3), and ulimit(3) do exist as library routines, so you're not fully abandoned. 🫶

The slot for phys(2) is in use since Linux 2.1.116 — it got taken over by umount(2), and phys(2) will never be implemented. Periodt. The getpmsg(2) and putpmsg(2) calls are for kernels patched to support STREAMS, and they may never be in the standard kernel either. 🙈

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. It was a whole main character for like five minutes. 💀

✨ System calls on removed ports ✨

Some system calls only ever existed on Linux architectures that have since been removed from the kernel. Like, gone gone. 🦋

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)
• 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) (added in Linux 3.9)
• metag_set_fpu_flags(2) (added in Linux 3.9)
• metag_set_tls(2) (added in Linux 3.9)
• metag_setglobalbit(2) (added in Linux 3.9)

Tile (port removed in Linux 4.17)

• cmpxchg_badaddr(2) (added in Linux 2.6.36)

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📝 NOTES 📝

Roughly speaking (roughly, babes, don't come for me), 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. ikr. 😭 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 system 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(). the way that history lingers... iconic honestly 👑

🦋 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). two for one, we love efficiency ✨
• 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 UID and effective UID 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.

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🌈 SEE ALSO 🌈

• intro(2)
• syscall(2)
• unimplemented(2)
• errno(3)
• libc(7)
• vdso(7)
• ausyscall(8)

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and that's a wrap on the whole page, bestie!! 🎀 This one's from Linux man-pages 6.20, dated 2026-02-08 — go forth and syscall responsibly, mwah 💖🌸🫶