syscalls(2) — Linux manual page


syscalls(2)                System Calls Manual               syscalls(2)

NAME         top

       syscalls - Linux system calls

SYNOPSIS         top

       Linux system calls.

DESCRIPTION         top

       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 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
       chown32(2)                  2.4
       chroot(2)                   1.0
       clock_adjtime(2)            2.6.39
       clock_getres(2)             2.6
       clock_gettime(2)            2.6
       clock_nanosleep(2)          2.6
       clock_settime(2)            2.6
       clone2(2)                   2.4           IA-64 only
       clone(2)                    1.0
       clone3(2)                   5.3
       close(2)                    1.0
       close_range(2)              5.9
       connect(2)                  2.0           See notes on socketcall(2)
       copy_file_range(2)          4.5
       creat(2)                    1.0
       create_module(2)            1.0           Removed in 2.6
       delete_module(2)            1.0
       dup(2)                      1.0
       dup2(2)                     1.0
       dup3(2)                     2.6.27
       epoll_create(2)             2.6
       epoll_create1(2)            2.6.27
       epoll_ctl(2)                2.6
       epoll_pwait(2)              2.6.19
       epoll_pwait2(2)             5.11
       epoll_wait(2)               2.6
       eventfd(2)                  2.6.22
       eventfd2(2)                 2.6.27
       execv(2)                    2.0           SPARC/SPARC64 only, for
                                                 compatibility with SunOS
       execve(2)                   1.0
       execveat(2)                 3.19
       exit(2)                     1.0
       exit_group(2)               2.6
       faccessat(2)                2.6.16
       faccessat2(2)               5.8
       fadvise64(2)                2.6
       fadvise64_64(2)             2.6
       fallocate(2)                2.6.23
       fanotify_init(2)            2.6.37
       fanotify_mark(2)            2.6.37
       fchdir(2)                   1.0
       fchmod(2)                   1.0
       fchmodat(2)                 2.6.16
       fchown(2)                   1.0
       fchown32(2)                 2.4
       fchownat(2)                 2.6.16
       fcntl(2)                    1.0
       fcntl64(2)                  2.4
       fdatasync(2)                2.0
       fgetxattr(2)                2.6; 2.4.18
       finit_module(2)             3.8
       flistxattr(2)               2.6; 2.4.18
       flock(2)                    2.0
       fork(2)                     1.0
       free_hugepages(2)           2.5.36        Removed in 2.5.44
       fremovexattr(2)             2.6; 2.4.18
       fsconfig(2)                 5.2
       fsetxattr(2)                2.6; 2.4.18
       fsmount(2)                  5.2
       fsopen(2)                   5.2
       fspick(2)                   5.2
       fstat(2)                    1.0
       fstat64(2)                  2.4
       fstatat64(2)                2.6.16
       fstatfs(2)                  1.0
       fstatfs64(2)                2.6
       fsync(2)                    1.0
       ftruncate(2)                1.0
       ftruncate64(2)              2.4
       futex(2)                    2.6
       futimesat(2)                2.6.16
       get_kernel_syms(2)          1.0           Removed in 2.6
       get_mempolicy(2)            2.6.6
       get_robust_list(2)          2.6.17
       get_thread_area(2)          2.6
       get_tls(2)                  4.15          ARM OABI only, has __ARM_NR
       getcpu(2)                   2.6.19
       getcwd(2)                   2.2
       getdents(2)                 2.0
       getdents64(2)               2.4
       getdomainname(2)            2.2           SPARC, SPARC64; available
                                                 as osf_getdomainname(2) on
                                                 Alpha since Linux 2.0
       getdtablesize(2)            2.0           SPARC (removed in 2.6.26),
                                                 available on Alpha as
       getegid(2)                  1.0
       getegid32(2)                2.4
       geteuid(2)                  1.0
       geteuid32(2)                2.4
       getgid(2)                   1.0
       getgid32(2)                 2.4
       getgroups(2)                1.0
       getgroups32(2)              2.4
       gethostname(2)              2.0           Alpha, was available on
                                                 SPARC up to Linux 2.6.26
       getitimer(2)                1.0
       getpeername(2)              2.0           See notes on socketcall(2)
       getpagesize(2)              2.0           Alpha, SPARC/SPARC64 only
       getpgid(2)                  1.0
       getpgrp(2)                  1.0
       getpid(2)                   1.0
       getppid(2)                  1.0
       getpriority(2)              1.0
       getrandom(2)                3.17
       getresgid(2)                2.2
       getresgid32(2)              2.4
       getresuid(2)                2.2
       getresuid32(2)              2.4
       getrlimit(2)                1.0
       getrusage(2)                1.0
       getsid(2)                   2.0
       getsockname(2)              2.0           See notes on socketcall(2)
       getsockopt(2)               2.0           See notes on socketcall(2)
       gettid(2)                   2.4.11
       gettimeofday(2)             1.0
       getuid(2)                   1.0
       getuid32(2)                 2.4
       getunwind(2)                2.4.8         IA-64 only; deprecated
       getxattr(2)                 2.6; 2.4.18
       getxgid(2)                  2.0           Alpha only; see NOTES
       getxpid(2)                  2.0           Alpha only; see NOTES
       getxuid(2)                  2.0           Alpha only; see NOTES
       init_module(2)              1.0
       inotify_add_watch(2)        2.6.13
       inotify_init(2)             2.6.13
       inotify_init1(2)            2.6.27
       inotify_rm_watch(2)         2.6.13
       io_cancel(2)                2.6
       io_destroy(2)               2.6
       io_getevents(2)             2.6
       io_pgetevents(2)            4.18
       io_setup(2)                 2.6
       io_submit(2)                2.6
       io_uring_enter(2)           5.1
       io_uring_register(2)        5.1
       io_uring_setup(2)           5.1
       ioctl(2)                    1.0
       ioperm(2)                   1.0
       iopl(2)                     1.0
       ioprio_get(2)               2.6.13
       ioprio_set(2)               2.6.13
       ipc(2)                      1.0
       kcmp(2)                     3.5
       kern_features(2)            3.7           SPARC64 only
       kexec_file_load(2)          3.17
       kexec_load(2)               2.6.13
       keyctl(2)                   2.6.10
       kill(2)                     1.0
       landlock_add_rule(2)        5.13
       landlock_create_ruleset(2)  5.13
       landlock_restrict_self(2)   5.13
       lchown(2)                   1.0           See chown(2) for version
       lchown32(2)                 2.4
       lgetxattr(2)                2.6; 2.4.18
       link(2)                     1.0
       linkat(2)                   2.6.16
       listen(2)                   2.0           See notes on socketcall(2)
       listxattr(2)                2.6; 2.4.18
       llistxattr(2)               2.6; 2.4.18
       lookup_dcookie(2)           2.6
       lremovexattr(2)             2.6; 2.4.18
       lseek(2)                    1.0
       lsetxattr(2)                2.6; 2.4.18
       lstat(2)                    1.0
       lstat64(2)                  2.4
       madvise(2)                  2.4
       mbind(2)                    2.6.6
       memory_ordering(2)          2.2           SPARC64 only
       membarrier(2)               3.17
       memfd_create(2)             3.17
       memfd_secret(2)             5.14
       migrate_pages(2)            2.6.16
       mincore(2)                  2.4
       mkdir(2)                    1.0
       mkdirat(2)                  2.6.16
       mknod(2)                    1.0
       mknodat(2)                  2.6.16
       mlock(2)                    2.0
       mlock2(2)                   4.4
       mlockall(2)                 2.0
       mmap(2)                     1.0
       mmap2(2)                    2.4
       modify_ldt(2)               1.0
       mount(2)                    1.0
       move_mount(2)               5.2
       move_pages(2)               2.6.18
       mprotect(2)                 1.0
       mq_getsetattr(2)            2.6.6
       mq_notify(2)                2.6.6
       mq_open(2)                  2.6.6
       mq_timedreceive(2)          2.6.6
       mq_timedsend(2)             2.6.6
       mq_unlink(2)                2.6.6
       mremap(2)                   2.0
       msgctl(2)                   2.0           See notes on ipc(2)
       msgget(2)                   2.0           See notes on ipc(2)
       msgrcv(2)                   2.0           See notes on ipc(2)
       msgsnd(2)                   2.0           See notes on ipc(2)
       msync(2)                    2.0
       munlock(2)                  2.0
       munlockall(2)               2.0
       munmap(2)                   1.0
       name_to_handle_at(2)        2.6.39
       nanosleep(2)                2.0
       newfstatat(2)               2.6.16        See stat(2)
       nfsservctl(2)               2.2           Removed in 3.1
       nice(2)                     1.0
       old_adjtimex(2)             2.0           Alpha only; see NOTES
       old_getrlimit(2)            2.4           Old variant of getrlimit(2)
                                                 that used a different value
                                                 for RLIM_INFINITY
       oldfstat(2)                 1.0
       oldlstat(2)                 1.0
       oldolduname(2)              1.0
       oldstat(2)                  1.0
       oldumount(2)                2.4.116       Name of the old umount(2)
                                                 syscall on Alpha
       olduname(2)                 1.0
       open(2)                     1.0
       open_by_handle_at(2)        2.6.39
       open_tree(2)                5.2
       openat(2)                   2.6.16
       openat2(2)                  5.6
       or1k_atomic(2)              3.1           OpenRISC 1000 only
       pause(2)                    1.0
       pciconfig_iobase(2)         2.2.15; 2.4   Not on x86
       pciconfig_read(2)           2.0.26; 2.2   Not on x86
       pciconfig_write(2)          2.0.26; 2.2   Not on x86
       perf_event_open(2)          2.6.31        Was perf_counter_open() in
                                                 2.6.31; renamed in 2.6.32
       personality(2)              1.2
       perfctr(2)                  2.2           SPARC only; removed in
       perfmonctl(2)               2.4           IA-64 only; removed in 5.10
       pidfd_getfd(2)              5.6
       pidfd_send_signal(2)        5.1
       pidfd_open(2)               5.3
       pipe(2)                     1.0
       pipe2(2)                    2.6.27
       pivot_root(2)               2.4
       pkey_alloc(2)               4.8
       pkey_free(2)                4.8
       pkey_mprotect(2)            4.8
       poll(2)                     2.0.36; 2.2
       ppoll(2)                    2.6.16
       prctl(2)                    2.2
       pread64(2)                                Added as "pread" in 2.2;
                                                 renamed "pread64" in 2.6
       preadv(2)                   2.6.30
       preadv2(2)                  4.6
       prlimit64(2)                2.6.36
       process_madvise(2)          5.10
       process_vm_readv(2)         3.2
       process_vm_writev(2)        3.2
       pselect6(2)                 2.6.16
       ptrace(2)                   1.0
       pwrite64(2)                               Added as "pwrite" in 2.2;
                                                 renamed "pwrite64" in 2.6
       pwritev(2)                  2.6.30
       pwritev2(2)                 4.6
       query_module(2)             2.2           Removed in 2.6
       quotactl(2)                 1.0
       quotactl_fd(2)              5.14
       read(2)                     1.0
       readahead(2)                2.4.13
       readdir(2)                  1.0
       readlink(2)                 1.0
       readlinkat(2)               2.6.16
       readv(2)                    2.0
       reboot(2)                   1.0
       recv(2)                     2.0           See notes on socketcall(2)
       recvfrom(2)                 2.0           See notes on socketcall(2)
       recvmsg(2)                  2.0           See notes on socketcall(2)
       recvmmsg(2)                 2.6.33
       remap_file_pages(2)         2.6           Deprecated since 3.16
       removexattr(2)              2.6; 2.4.18
       rename(2)                   1.0
       renameat(2)                 2.6.16
       renameat2(2)                3.15
       request_key(2)              2.6.10
       restart_syscall(2)          2.6
       riscv_flush_icache(2)       4.15          RISC-V only
       rmdir(2)                    1.0
       rseq(2)                     4.18
       rt_sigaction(2)             2.2
       rt_sigpending(2)            2.2
       rt_sigprocmask(2)           2.2
       rt_sigqueueinfo(2)          2.2
       rt_sigreturn(2)             2.2
       rt_sigsuspend(2)            2.2
       rt_sigtimedwait(2)          2.2
       rt_tgsigqueueinfo(2)        2.6.31
       rtas(2)                     2.6.2         PowerPC/PowerPC64 only
       s390_runtime_instr(2)       3.7           s390 only
       s390_pci_mmio_read(2)       3.19          s390 only
       s390_pci_mmio_write(2)      3.19          s390 only
       s390_sthyi(2)               4.15          s390 only
       s390_guarded_storage(2)     4.12          s390 only
       sched_get_affinity(2)       2.6           Name of
                                                 sched_getaffinity(2) on
                                                 SPARC and SPARC64
       sched_get_priority_max(2)   2.0
       sched_get_priority_min(2)   2.0
       sched_getaffinity(2)        2.6
       sched_getattr(2)            3.14
       sched_getparam(2)           2.0
       sched_getscheduler(2)       2.0
       sched_rr_get_interval(2)    2.0
       sched_set_affinity(2)       2.6           Name of
                                                 sched_setaffinity(2) on
                                                 SPARC and SPARC64
       sched_setaffinity(2)        2.6
       sched_setattr(2)            3.14
       sched_setparam(2)           2.0
       sched_setscheduler(2)       2.0
       sched_yield(2)              2.0
       seccomp(2)                  3.17
       select(2)                   1.0
       semctl(2)                   2.0           See notes on ipc(2)
       semget(2)                   2.0           See notes on ipc(2)
       semop(2)                    2.0           See notes on ipc(2)
       semtimedop(2)               2.6; 2.4.22
       send(2)                     2.0           See notes on socketcall(2)
       sendfile(2)                 2.2
       sendfile64(2)               2.6; 2.4.19
       sendmmsg(2)                 3.0
       sendmsg(2)                  2.0           See notes on socketcall(2)
       sendto(2)                   2.0           See notes on socketcall(2)
       set_mempolicy(2)            2.6.6
       set_robust_list(2)          2.6.17
       set_thread_area(2)          2.6
       set_tid_address(2)          2.6
       set_tls(2)                  2.6.11        ARM OABI/EABI only
                                                 (constant has __ARM_NR
       setdomainname(2)            1.0
       setfsgid(2)                 1.2
       setfsgid32(2)               2.4
       setfsuid(2)                 1.2
       setfsuid32(2)               2.4
       setgid(2)                   1.0
       setgid32(2)                 2.4
       setgroups(2)                1.0
       setgroups32(2)              2.4
       sethae(2)                   2.0           Alpha only; see NOTES
       sethostname(2)              1.0
       setitimer(2)                1.0
       setns(2)                    3.0
       setpgid(2)                  1.0
       setpgrp(2)                  2.0           Alternative name for
                                                 setpgid(2) on Alpha
       setpriority(2)              1.0
       setregid(2)                 1.0
       setregid32(2)               2.4
       setresgid(2)                2.2
       setresgid32(2)              2.4
       setresuid(2)                2.2
       setresuid32(2)              2.4
       setreuid(2)                 1.0
       setreuid32(2)               2.4
       setrlimit(2)                1.0
       setsid(2)                   1.0
       setsockopt(2)               2.0           See notes on socketcall(2)
       settimeofday(2)             1.0
       setuid(2)                   1.0
       setuid32(2)                 2.4
       setup(2)                    1.0           Removed in 2.2
       setxattr(2)                 2.6; 2.4.18
       sgetmask(2)                 1.0
       shmat(2)                    2.0           See notes on ipc(2)
       shmctl(2)                   2.0           See notes on ipc(2)
       shmdt(2)                    2.0           See notes on ipc(2)
       shmget(2)                   2.0           See notes on ipc(2)
       shutdown(2)                 2.0           See notes on socketcall(2)
       sigaction(2)                1.0
       sigaltstack(2)              2.2
       signal(2)                   1.0
       signalfd(2)                 2.6.22
       signalfd4(2)                2.6.27
       sigpending(2)               1.0
       sigprocmask(2)              1.0
       sigreturn(2)                1.0
       sigsuspend(2)               1.0
       socket(2)                   2.0           See notes on socketcall(2)
       socketcall(2)               1.0
       socketpair(2)               2.0           See notes on socketcall(2)
       spill(2)                    2.6.13        Xtensa only
       splice(2)                   2.6.17
       spu_create(2)               2.6.16        PowerPC/PowerPC64 only
       spu_run(2)                  2.6.16        PowerPC/PowerPC64 only
       ssetmask(2)                 1.0
       stat(2)                     1.0
       stat64(2)                   2.4
       statfs(2)                   1.0
       statfs64(2)                 2.6
       statx(2)                    4.11
       stime(2)                    1.0
       subpage_prot(2)             2.6.25        PowerPC/PowerPC64 only
       swapcontext(2)              2.6.3         PowerPC/PowerPC64 only
       switch_endian(2)            4.1           PowerPC64 only
       swapoff(2)                  1.0
       swapon(2)                   1.0
       symlink(2)                  1.0
       symlinkat(2)                2.6.16
       sync(2)                     1.0
       sync_file_range(2)          2.6.17
       sync_file_range2(2)         2.6.22
       syncfs(2)                   2.6.39
       sys_debug_setcontext(2)     2.6.11        PowerPC only
       syscall(2)                  1.0           Still available on ARM OABI
                                                 and MIPS O32 ABI
       sysfs(2)                    1.2
       sysinfo(2)                  1.0
       syslog(2)                   1.0
       sysmips(2)                  2.6.0         MIPS only
       tee(2)                      2.6.17
       tgkill(2)                   2.6
       time(2)                     1.0
       timer_create(2)             2.6
       timer_delete(2)             2.6
       timer_getoverrun(2)         2.6
       timer_gettime(2)            2.6
       timer_settime(2)            2.6
       timerfd_create(2)           2.6.25
       timerfd_gettime(2)          2.6.25
       timerfd_settime(2)          2.6.25
       times(2)                    1.0
       tkill(2)                    2.6; 2.4.22
       truncate(2)                 1.0
       truncate64(2)               2.4
       ugetrlimit(2)               2.4
       umask(2)                    1.0
       umount(2)                   1.0
       umount2(2)                  2.2
       uname(2)                    1.0
       unlink(2)                   1.0
       unlinkat(2)                 2.6.16
       unshare(2)                  2.6.16
       uselib(2)                   1.0
       ustat(2)                    1.0
       userfaultfd(2)              4.3
       usr26(2)                 ARM OABI only
       usr32(2)                 ARM OABI only
       utime(2)                    1.0
       utimensat(2)                2.6.22
       utimes(2)                   2.2
       utrap_install(2)            2.2           SPARC64 only
       vfork(2)                    2.2
       vhangup(2)                  1.0
       vm86old(2)                  1.0           Was "vm86"; renamed in
       vm86(2)                     2.0.28; 2.2
       vmsplice(2)                 2.6.17
       wait4(2)                    1.0
       waitid(2)                   2.6.10
       waitpid(2)                  1.0
       write(2)                    1.0
       writev(2)                   2.0
       xtensa(2)                   2.6.13        Xtensa only

       On many platforms, including x86-32, socket calls are all
       multiplexed (via glibc wrapper functions) through socketcall(2)
       and similarly System V IPC calls are multiplexed through 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.

   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)

NOTES         top

       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

       •  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"

          On newer platforms that only have 64-bit file access and
          32-bit UIDs/GIDs (e.g., alpha, ia64, s390x, x86-64), there is
          just a single version of the UID/GID and file access system
          calls.  On platforms (typically, 32-bit platforms) where the
          *64 and *32 calls exist, the other versions are obsolete.

       •  The rt_sig* calls were added in Linux 2.2 to support the
          addition of real-time signals (see signal(7)).  These system
          calls supersede the older system calls of the same name
          without the "rt_" prefix.

       •  The select(2) and mmap(2) system calls use five or more
          arguments, which caused problems in the way argument passing
          on the i386 used to be set up.  Thus, while other
          architectures have sys_select() and sys_mmap() corresponding
          to __NR_select and __NR_mmap, on i386 one finds old_select()
          and old_mmap() (routines that use a pointer to an argument
          block) instead.  These days passing five arguments is not a
          problem any more, and there is a __NR__newselect that
          corresponds directly to sys_select() and similarly __NR_mmap2.
          s390x is the only 64-bit architecture that has old_mmap().

   Architecture-specific details: Alpha
              returns a pair of GID and effective GID via registers r0
              and r20; it is provided instead of getgid(2) and

              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

              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         top

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

COLOPHON         top

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       user-space interface documentation) project.  Information about
       the project can be found at 
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       for this manual page, see
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Linux man-pages 6.9.1          2024-05-02                    syscalls(2)

Pages that refer to this page: strace(1)intro(2)syscall(2)unimplemented(2)stapprobes(3stap)libc(7)man-pages(7)vdso(7)