syscalls - Linux system calls
Linux system calls.The system call is the fundamental interface between an application and the Linux kernel.
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.
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 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 5.5 |
| 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 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 | |
| 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 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 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 | |
| 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 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 |
| 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 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) | 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 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 |
| 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) | 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 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.
Some system calls only ever existed on Linux architectures that have since been removed from the kernel:
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_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)
cmpxchg_badaddr(2) (added in Linux 2.6.36)
Roughly speaking, the code belonging to the system call with number
__NR_xxx defined in /usr/include/asm/unistd.h can be found in
the Linux kernel source in the routine sys_xxx(). There are
many exceptions, however, mostly because older system calls were
superseded by newer ones, and this has been treated somewhat
unsystematically. On platforms with proprietary operating-system
emulation, such as sparc, sparc64, and alpha, there are many additional
system calls; mips64 also contains a full set of 32-bit system
calls.
Over time, changes to the interfaces of some system calls have been necessary. One reason for such changes was the need to increase the size of structures or scalar values passed to the system call. Because of these changes, 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().
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 OSF/1.
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.