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,  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
       truncate() which invokes the underlying "truncate" system call.

       Often the glibc wrapper function is quite thin, doing little work other
       than copying arguments to the right registers before invoking the  sys-
       tem  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 wrap-
       per function is provided.)  Note: system calls indicate  a  failure  by
       returning a negative error number to the caller; when this happens, the
       wrapper function negates the returned error number (to  make  it  posi-
       tive), 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 trun-
       cate64(2), and the glibc truncate() wrapper function  checks  which  of
       those  system  calls  are  provided  by the kernel and determines which
       should be employed.

   System call list
       Below is a list of the Linux system calls.  In  the  list,  the  Kernel
       column  indicates  the  kernel version for those system calls that were
       new in Linux 2.2, or have appeared since that kernel version.  Note the
       following points:

       *  Where  no  kernel  version is indicated, the system call appeared in
          kernel 1.0 or earlier.

       *  Where a system call is marked "1.2" this means the system call prob-
          ably  appeared  in  a  1.1.x kernel version, and first appeared in a
          stable kernel with 1.2.  (Development of the 1.2 kernel  was  initi-
          ated  from  a  branch  of kernel 1.0.6 via the 1.1.x unstable kernel

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

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

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

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

       The  list  of system calls that are available as at kernel 3.9 (or in a
       few cases only on older kernels) is as follows:

       System call                 Kernel        Notes

       _llseek(2)                  1.2
       _newselect(2)               2.0
       _sysctl(2)                  2.0
       accept(2)                   2.0           See notes on socketcall(2)
       accept4(2)                  2.6.28
       access(2)                   1.0
       acct(2)                     1.0
       add_key(2)                  2.6.11
       adjtimex(2)                 1.0
       alarm(2)                    1.0
       alloc_hugepages(2)          2.5.36        Removed in 2.5.44
       bdflush(2)                  1.2           Deprecated (does nothing)
                                                 since 2.6
       bind(2)                     2.0           See notes on socketcall(2)
       brk(2)                      1.0
       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
       epoll_ctl(2)                2.6
       epoll_pwait(2)              2.6.19
       epoll_wait(2)               2.6
       eventfd(2)                  2.6.22
       eventfd2(2)                 2.6.27
       execve(2)                   1.0
       exit(2)                     1.0
       exit_group(2)               2.6
       faccessat(2)                2.6.16
       fadvise64(2)                2.6
       fadvise64_64(2)             2.6
       fallocate(2)                2.6.23
       fanotify_init(2)            2.6.37
       fanotify_mark(2)            2.6.37
       fchdir(2)                   1.0
       fchmod(2)                   1.0
       fchmodat(2)                 2.6.16
       fchown(2)                   1.0
       fchown32(2)                 2.4
       fchownat(2)                 2.6.16
       fcntl(2)                    1.0
       fcntl64(2)                  2.4
       fdatasync(2)                2.0
       fgetxattr(2)                2.6; 2.4.18
       finit_module(2)             3.8
       flistxattr(2)               2.6; 2.4.18
       flock(2)                    2.0
       fork(2)                     1.0
       free_hugepages(2)           2.5.36        Removed in 2.5.44
       fremovexattr(2)             2.6; 2.4.18
       fsetxattr(2)                2.6; 2.4.18
       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           1.0
       ftruncate(2)                1.0
       ftruncate64(2)              2.4
       futex(2)                    2.6
       futimesat(2)                2.6.16
       get_kernel_syms(2)                        Removed in 2.6
       get_mempolicy(2)            2.6.6
       get_robust_list(2)          2.6.17
       get_thread_area(2)          2.6
       getcpu(2)                   2.6.19
       getcwd(2)                   2.2
       getdents(2)                 2.0
       getdents64(2)               2.4
       getegid(2)                  1.0
       getegid32(2)                2.4
       geteuid(2)                  1.0
       geteuid32(2)                2.4
       getgid(2)                   1.0
       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
       getxattr(2)                 2.6; 2.4.18
       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_setup(2)                 2.6
       io_submit(2)                2.6
       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
       kexec_load(2)               2.6.13
       keyctl(2)                   2.6.11
       kill(2)                     1.0
       lchown(2)                   1.0           See chown(2) for
                                                 version details
       lchown32(2)                 2.4
       lgetxattr(2)                2.6; 2.4.18
       link(2)                     1.0
       linkat(2)                   2.6.16
       listen(2)                   2.0           See notes on socketcall(2)
       listxattr(2)                2.6; 2.4.18
       llistxattr(2)               2.6; 2.4.18
       lookup_dcookie(2)           2.6
       lremovexattr(2)             2.6; 2.4.18
       lseek(2)                    1.0
       lsetxattr(2)                2.6; 2.4.18
       lstat(2)                    1.0
       lstat64(2)                  2.4
       madvise(2)                  2.4
       madvise1(2)                 2.4
       mbind(2)                    2.6.6
       migrate_pages(2)            2.6.16
       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
       nfsservctl(2)               2.2           Removed in 3.1
       nice(2)                     1.0
       oldfstat(2)                 1.0
       oldlstat(2)                 1.0
       oldolduname(2)              1.0
       oldstat(2)                  1.0
       olduname(2)                 1.0
       open(2)                     1.0
       open_by_handle_at(2)        2.6.39
       openat(2)                   2.6.16
       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 called
                                                 in 2.6.31; renamed in
       personality(2)              1.2
       perfctr(2)                  2.2           Sparc; removed in 2.6.34
       perfmonctl(2)               2.4           ia64
       pipe(2)                     1.0
       pipe2(2)                    2.6.27
       pivot_root(2)               2.4
       poll(2)                     2.0.36; 2.2
       ppc_rtas(2)                               PowerPC only
       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
       prlimit(2)                  2.6.36
       process_vm_readv(2)         3.2
       process_vm_writev(2)        3.2
       pselect6(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
       removexattr(2)              2.6; 2.4.18
       rename(2)                   1.0
       renameat(2)                 2.6.16
       request_key(2)              2.6.11
       restart_syscall(2)          2.6
       rmdir(2)                    1.0
       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
       s390_runtime_instr(2)       3.7           s390 only
       sched_get_priority_max(2)   2.0
       sched_get_priority_min(2)   2.0
       sched_getaffinity(2)        2.6
       sched_getparam(2)           2.0
       sched_getscheduler(2)       2.0
       sched_rr_get_interval(2)    2.0
       sched_setaffinity(2)        2.6
       sched_setparam(2)           2.0
       sched_setscheduler(2)       2.0
       sched_yield(2)              2.0
       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
       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
       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)                                  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)
       splice(2)                   2.6.17
       spu_create(2)               2.6.16        PowerPC only
       spu_run(2)                  2.6.16        PowerPC only
       ssetmask(2)                 1.0
       stat(2)                     1.0
       stat64(2)                   2.4
       statfs(2)                   1.0
       statfs64(2)                 2.6
       stime(2)                    1.0
       subpage_prot(2)             2.6.25        PowerPC if
       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        Architecture-specific
                                                 variant of
       syncfs(2)                   2.6.39
       sysfs(2)                    1.2
       sysinfo(2)                  1.0
       syslog(2)                   1.0
       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
       utime(2)                    1.0
       utimensat(2)                2.6.22
       utimes(2)                   2.2
       utrap_install(2)            2.2           Sparc
       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

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

       Although slots are reserved for them in the system call table, the fol-
       lowing system  calls  are  not  implemented  in  the  standard  kernel:
       afs_syscall(2),   break(2),  ftime(2),  getpmsg(2),  gtty(2),  idle(2),
       lock(2), madvise1(2), mpx(2), phys(2), prof(2), profil(2),  putpmsg(2),
       security(2),  stty(2),  tuxcall(2), ulimit(2), and vserver(2) (see also
       unimplemented(2)).  However, ftime(3), profil(3) and ulimit(3) exist as
       library  routines.  The slot for phys(2) is in use since kernel 2.1.116
       for umount(2); phys(2) will never be implemented.  The  getpmsg(2)  and
       putpmsg(2)  calls  are  for kernels patched to support STREAMS, and may
       never be in the standard kernel.

       There was briefly  set_zone_reclaim(2),  added  in  Linux  2.6.13,  and
       removed in 2.6.16; this system call was never available to user space.

       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().  (The dispatch table for i386
       can be found in  /usr/src/linux/arch/i386/kernel/entry.S.)   There  are
       many exceptions, however, mostly because older system calls were super-
       functions do some work to ensure that the right system call is invoked,
       and that ABI compatibility is preserved for old binaries.)  Examples of
       systems calls that exist in multiple versions are the following:

       *  By now there are three different  versions  of  stat(2):  sys_stat()
          (slot    __NR_oldstat),    sys_newstat()   (slot   __NR_stat),   and
          sys_stat64() (slot __NR_stat64), with the last being the  most  cur-
          rent.  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

       *  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, replace-
          ments were required for system calls that deal with file offsets and
          sizes.   Thus  the  following  system  calls were added: fcntl64(2),
          ftruncate64(2), getdents64(2),  stat64(2),  statfs64(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" suf-

          On newer platforms that only have 64-bit file access and 32-bit uids
          (e.g., alpha, ia64, s390x) there are no *64 or *32 calls.  Where the
          *64 and *32 calls exist, the other versions are obsolete.

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

       *  The select(2) and mmap(2) system calls use five or  more  arguments,
          which  caused  problems in the way argument passing on the i386 used
          to be set up.  Thus, while other architectures have sys_select() and
          sys_mmap()  corresponding  to __NR_select and __NR_mmap, on i386 one
          finds old_select() and old_mmap() (routines that use a pointer to  a
          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.

Man Pages Copyright Respective Owners. Site Copyright (C) 1994 - 2019 Hurricane Electric. All Rights Reserved.