syscalls(2)
NAME
syscalls - Linux system calls
SYNOPSIS
Linux system calls.
DESCRIPTION
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 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; 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 kernel 1.0 or earlier. * Where a system call is marked "1.2" this means the system call probably 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 initiated from a branch of kernel 1.0.6 via the 1.1.x unstable kernel series.) * Where a system call is marked "2.0" this means the system call probably 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 initiated 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 "2.2" this means the system call probably appeared in a 2.1.x kernel version, and first appeared in a stable kernel with 2.2.0. (Development of the 2.2 kernel was initiated from a branch of kernel 2.0.21 via the 2.1.x unstable kernel series.) * Where a system call is marked "2.4" this means the system call probably appeared in a 2.3.x kernel version, and first appeared in a stable kernel with 2.4.0. (Development of the 2.4 kernel was initiated from a branch of kernel 2.2.8 via the 2.3.x unstable kernel series.) * Where a system call is marked "2.6" this means the system call probably 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 series.) * 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, and the 4.x kernel series, which followed on from kernel 3.19. * 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 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 4.9 (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) bpf(2) 3.18 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 clone(2) 1.0 close(2) 1.0 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_wait(2) 2.6 eventfd(2) 2.6.22 eventfd2(2) 2.6.27 execve(2) 1.0 execveat(2) 3.19 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 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 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 getgid32(2) 2.4 getgroups(2) 1.0 getgroups32(2) 2.4 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 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_file_load(2) 3.17 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 mbind(2) 2.6.6 memfd_create(2) 3.17 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_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 perf_counter_open() in 2.6.31; renamed in 2.6.32 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 pkey_alloc(2) 4.8 pkey_free(2) 4.8 pkey_mprotect(2) 4.8 poll(2) 2.0.36; 2.2 ppc_rtas(2) 2.6.2 PowerPC only ppc_swapcontext(2) 2.6.3 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 preadv2(2) 4.6 prlimit64(2) 2.6.36 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 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) 2.6.11 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 s390_pci_mmio_read(2) 3.19 s390 only s390_pci_mmio_write(2) 3.19 s390 only 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_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 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 sethostname(2) 1.0 setitimer(2) 1.0 setns(2) 3.0 setpgid(2) 1.0 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) 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 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 sysfs(2) 1.2 sysinfo(2) 1.0 syslog(2) 1.0 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) 4.2 utime(2) 1.0 utimensat(2) 2.6.22 utimes(2) 2.2 utrap_install(2) 2.2 Sparc 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 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 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.
NOTES
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 superseded by newer ones, and this has been treated somewhat unsystematically. On platforms with proprietary operating-system emulation, such as parisc, 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 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 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 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 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.
SEE ALSO
intro(2), syscall(2), unimplemented(2), errno(3), libc(7), vdso(7)
COLOPHON
This page is part of release 4.09 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.
Opportunity
Personal Opportunity - Free software gives you access to billions of dollars of software at no cost. Use this software for your business, personal use or to develop a profitable skill. Access to source code provides access to a level of capabilities/information that companies protect though copyrights. Open source is a core component of the Internet and it is available to you. Leverage the billions of dollars in resources and capabilities to build a career, establish a business or change the world. The potential is endless for those who understand the opportunity.
Business Opportunity - Goldman Sachs, IBM and countless large corporations are leveraging open source to reduce costs, develop products and increase their bottom lines. Learn what these companies know about open source and how open source can give you the advantage.
Free Software
Free Software provides computer programs and capabilities at no cost but more importantly, it provides the freedom to run, edit, contribute to, and share the software. The importance of free software is a matter of access, not price. Software at no cost is a benefit but ownership rights to the software and source code is far more significant.
Free Office Software - The Libre Office suite provides top desktop productivity tools for free. This includes, a word processor, spreadsheet, presentation engine, drawing and flowcharting, database and math applications. Libre Office is available for Linux or Windows.
Free Books
The Free Books Library is a collection of thousands of the most popular public domain books in an online readable format. The collection includes great classical literature and more recent works where the U.S. copyright has expired. These books are yours to read and use without restrictions.
Source Code - Want to change a program or know how it works? Open Source provides the source code for its programs so that anyone can use, modify or learn how to write those programs themselves. Visit the GNU source code repositories to download the source.
Education
Study at Harvard, Stanford or MIT - Open edX provides free online courses from Harvard, MIT, Columbia, UC Berkeley and other top Universities. Hundreds of courses for almost all major subjects and course levels. Open edx also offers some paid courses and selected certifications.
Linux Manual Pages - A man or manual page is a form of software documentation found on Linux/Unix operating systems. Topics covered include computer programs (including library and system calls), formal standards and conventions, and even abstract concepts.
