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SIGNAL(7)                                                               Linux Programmer's Manual                                                              SIGNAL(7)

NAME
       signal - overview of signals

DESCRIPTION
       Linux supports both POSIX reliable signals (hereinafter "standard signals") and POSIX real-time signals.

   Signal dispositions
       Each signal has a current disposition, which determines how the process behaves when it is delivered the signal.

       The entries in the "Action" column of the table below specify the default disposition for each signal, as follows:

       Term   Default action is to terminate the process.

       Ign    Default action is to ignore the signal.

       Core   Default action is to terminate the process and dump core (see core(5)).

       Stop   Default action is to stop the process.

       Cont   Default action is to continue the process if it is currently stopped.

       A process can change the disposition of a signal using sigaction(2) or signal(2).  (The latter is less portable when establishing a signal handler; see signal(2)
       for details.)  Using these system calls, a process can elect one of the following behaviors to occur on delivery of the signal: perform the default  action;  ig‐
       nore the signal; or catch the signal with a signal handler, a programmer-defined function that is automatically invoked when the signal is delivered.

       By  default,  a  signal  handler  is invoked on the normal process stack.  It is possible to arrange that the signal handler uses an alternate stack; see sigalt‐
       stack(2) for a discussion of how to do this and when it might be useful.

       The signal disposition is a per-process attribute: in a multithreaded application, the disposition of a particular signal is the same for all threads.

       A child created via fork(2) inherits a copy of its parent's signal dispositions.  During an execve(2), the dispositions of handled signals are reset to  the  de‐
       fault; the dispositions of ignored signals are left unchanged.

   Sending a signal
       The following system calls and library functions allow the caller to send a signal:

       raise(3)
              Sends a signal to the calling thread.

       kill(2)
              Sends a signal to a specified process, to all members of a specified process group, or to all processes on the system.

       pidfd_send_signal(2)
              Sends a signal to a process identified by a PID file descriptor.

       killpg(3)
              Sends a signal to all of the members of a specified process group.

       pthread_kill(3)
              Sends a signal to a specified POSIX thread in the same process as the caller.

       tgkill(2)
              Sends a signal to a specified thread within a specific process.  (This is the system call used to implement pthread_kill(3).)

       sigqueue(3)
              Sends a real-time signal with accompanying data to a specified process.

   Waiting for a signal to be caught
       The following system calls suspend execution of the calling thread until a signal is caught (or an unhandled signal terminates the process):

       pause(2)
              Suspends execution until any signal is caught.

       sigsuspend(2)
              Temporarily changes the signal mask (see below) and suspends execution until one of the unmasked signals is caught.

   Synchronously accepting a signal
       Rather  than asynchronously catching a signal via a signal handler, it is possible to synchronously accept the signal, that is, to block execution until the sig‐
       nal is delivered, at which point the kernel returns information about the signal to the caller.  There are two general ways to do this:

       * sigwaitinfo(2), sigtimedwait(2), and sigwait(3) suspend execution until one of the signals in a specified set is delivered.  Each of these calls returns infor‐
         mation about the delivered signal.

       * signalfd(2)  returns  a  file  descriptor that can be used to read information about signals that are delivered to the caller.  Each read(2) from this file de‐
         scriptor blocks until one of the signals in the set specified in the signalfd(2) call is delivered to the caller.  The buffer returned by  read(2)  contains  a
         structure describing the signal.

   Signal mask and pending signals
       A signal may be blocked, which means that it will not be delivered until it is later unblocked.  Between the time when it is generated and when it is delivered a
       signal is said to be pending.

       Each thread in a process has an independent signal mask, which indicates the set of signals that the thread is currently blocking.  A thread can  manipulate  its
       signal mask using pthread_sigmask(3).  In a traditional single-threaded application, sigprocmask(2) can be used to manipulate the signal mask.

       A child created via fork(2) inherits a copy of its parent's signal mask; the signal mask is preserved across execve(2).

       A signal may be process-directed or thread-directed.  A process-directed signal is one that is targeted at (and thus pending for) the process as a whole.  A sig‐
       nal may be process-directed because it was generated by the kernel for reasons other than a  hardware  exception,  or  because  it  was  sent  using  kill(2)  or
       sigqueue(3).   A  thread-directed signal is one that is targeted at a specific thread.  A signal may be thread-directed because it was generated as a consequence
       of executing a specific machine-language instruction that triggered a hardware exception (e.g., SIGSEGV for an invalid memory access, or SIGFPE for  a  math  er‐
       ror), or because it was targeted at a specific thread using interfaces such as tgkill(2) or pthread_kill(3).

       A  process-directed  signal  may be delivered to any one of the threads that does not currently have the signal blocked.  If more than one of the threads has the
       signal unblocked, then the kernel chooses an arbitrary thread to which to deliver the signal.

       A thread can obtain the set of signals that it currently has pending using sigpending(2).  This set will consist of the union of the set of  pending  process-di‐
       rected signals and the set of signals pending for the calling thread.

       A child created via fork(2) initially has an empty pending signal set; the pending signal set is preserved across an execve(2).

   Execution of signal handlers
       Whenever  there  is  a transition from kernel-mode to user-mode execution (e.g., on return from a system call or scheduling of a thread onto the CPU), the kernel
       checks whether there is a pending unblocked signal for which the process has established a signal handler.  If there is such  a  pending  signal,  the  following
       steps occur:

       1. The kernel performs the necessary preparatory steps for execution of the signal handler:

          a) The signal is removed from the set of pending signals.

          b) If  the signal handler was installed by a call to sigaction(2) that specified the SA_ONSTACK flag and the thread has defined an alternate signal stack (us‐
             ing sigaltstack(2)), then that stack is installed.

          c) Various pieces of signal-related context are saved into a special frame that is created on the stack.  The saved information includes:

             + the program counter register (i.e., the address of the next instruction in the main program that should be executed when the signal handler returns);

             + architecture-specific register state required for resuming the interrupted program;

             + the thread's current signal mask;

             + the thread's alternate signal stack settings.

             (If the signal handler was installed using the sigaction(2) SA_SIGINFO flag, then the above information is accessible via the  ucontext_t  object  that  is
             pointed to by the third argument of the signal handler.)

          d) Any  signals  specified in act->sa_mask when registering the handler with sigprocmask(2) are added to the thread's signal mask.  The signal being delivered
             is also added to the signal mask, unless SA_NODEFER was specified when registering the handler.  These signals are thus blocked while the handler executes.

       2. The kernel constructs a frame for the signal handler on the stack.  The kernel sets the program counter for the thread to point to the  first  instruction  of
          the  signal  handler  function, and configures the return address for that function to point to a piece of user-space code known as the signal trampoline (de‐
          scribed in sigreturn(2)).

       3. The kernel passes control back to user-space, where execution commences at the start of the signal handler function.

       4. When the signal handler returns, control passes to the signal trampoline code.

       5. The signal trampoline calls sigreturn(2), a system call that uses the information in the stack frame created in step 1 to restore the thread to its state  be‐
          fore  the signal handler was called.  The thread's signal mask and alternate signal stack settings are restored as part of this procedure.  Upon completion of
          the call to sigreturn(2), the kernel transfers control back to user space, and the thread recommences execution at the point where it was interrupted  by  the
          signal handler.

       Note  that if the signal handler does not return (e.g., control is transferred out of the handler using siglongjmp(3), or the handler executes a new program with
       execve(2)), then the final step is not performed.  In particular, in such scenarios it is the programmer's responsibility to restore the state of the signal mask
       (using  sigprocmask(2)),  if  it is desired to unblock the signals that were blocked on entry to the signal handler.  (Note that siglongjmp(3) may or may not re‐
       store the signal mask, depending on the savesigs value that was specified in the corresponding call to sigsetjmp(3).)

       From the kernel's point of view, execution of the signal handler code is exactly the same as the execution of any other user-space code.  That  is  to  say,  the
       kernel  does not record any special state information indicating that the thread is currently executing inside a signal handler.  All necessary state information
       is maintained in user-space registers and the user-space stack.  The depth to which nested signal handlers may be invoked is thus limited only by the  user-space
       stack (and sensible software design!).

   Standard signals
       Linux  supports the standard signals listed below.  The second column of the table indicates which standard (if any) specified the signal: "P1990" indicates that
       the signal is described in the original POSIX.1-1990 standard; "P2001" indicates that the signal was added in SUSv2 and POSIX.1-2001.

       Signal      Standard   Action   Comment
       ────────────────────────────────────────────────────────────────────────
       SIGABRT      P1990      Core    Abort signal from abort(3)
       SIGALRM      P1990      Term    Timer signal from alarm(2)
       SIGBUS       P2001      Core    Bus error (bad memory access)
       SIGCHLD      P1990      Ign     Child stopped or terminated
       SIGCLD         -        Ign     A synonym for SIGCHLD
       SIGCONT      P1990      Cont    Continue if stopped
       SIGEMT         -        Term    Emulator trap
       SIGFPE       P1990      Core    Floating-point exception
       SIGHUP       P1990      Term    Hangup detected on controlling terminal
                                       or death of controlling process
       SIGILL       P1990      Core    Illegal Instruction
       SIGINFO        -                A synonym for SIGPWR
       SIGINT       P1990      Term    Interrupt from keyboard
       SIGIO          -        Term    I/O now possible (4.2BSD)
       SIGIOT         -        Core    IOT trap. A synonym for SIGABRT
       SIGKILL      P1990      Term    Kill signal
       SIGLOST        -        Term    File lock lost (unused)
       SIGPIPE      P1990      Term    Broken pipe: write to pipe with no
                                       readers; see pipe(7)
       SIGPOLL      P2001      Term    Pollable event (Sys V);
                                       synonym for SIGIO
       SIGPROF      P2001      Term    Profiling timer expired
       SIGPWR         -        Term    Power failure (System V)
       SIGQUIT      P1990      Core    Quit from keyboard
       SIGSEGV      P1990      Core    Invalid memory reference
       SIGSTKFLT      -        Term    Stack fault on coprocessor (unused)
       SIGSTOP      P1990      Stop    Stop process
       SIGTSTP      P1990      Stop    Stop typed at terminal
       SIGSYS       P2001      Core    Bad system call (SVr4);
                                       see also seccomp(2)
       SIGTERM      P1990      Term    Termination signal
       SIGTRAP      P2001      Core    Trace/breakpoint trap
       SIGTTIN      P1990      Stop    Terminal input for background process
       SIGTTOU      P1990      Stop    Terminal output for background process
       SIGUNUSED      -        Core    Synonymous with SIGSYS
       SIGURG       P2001      Ign     Urgent condition on socket (4.2BSD)
       SIGUSR1      P1990      Term    User-defined signal 1
       SIGUSR2      P1990      Term    User-defined signal 2
       SIGVTALRM    P2001      Term    Virtual alarm clock (4.2BSD)

       SIGXCPU      P2001      Core    CPU time limit exceeded (4.2BSD);
                                       see setrlimit(2)
       SIGXFSZ      P2001      Core    File size limit exceeded (4.2BSD);
                                       see setrlimit(2)
       SIGWINCH       -        Ign     Window resize signal (4.3BSD, Sun)

       The signals SIGKILL and SIGSTOP cannot be caught, blocked, or ignored.

       Up to and including Linux 2.2, the default behavior for SIGSYS, SIGXCPU, SIGXFSZ, and (on architectures other than SPARC and MIPS) SIGBUS was  to  terminate  the
       process  (without  a core dump).  (On some other UNIX systems the default action for SIGXCPU and SIGXFSZ is to terminate the process without a core dump.)  Linux
       2.4 conforms to the POSIX.1-2001 requirements for these signals, terminating the process with a core dump.

       SIGEMT is not specified in POSIX.1-2001, but nevertheless appears on most other UNIX systems, where its default action is typically to terminate the process with
       a core dump.

       SIGPWR (which is not specified in POSIX.1-2001) is typically ignored by default on those other UNIX systems where it appears.

       SIGIO (which is not specified in POSIX.1-2001) is ignored by default on several other UNIX systems.

   Queueing and delivery semantics for standard signals
       If multiple standard signals are pending for a process, the order in which the signals are delivered is unspecified.

       Standard  signals  do  not queue.  If multiple instances of a standard signal are generated while that signal is blocked, then only one instance of the signal is
       marked as pending (and the signal will be delivered just once when it is unblocked).  In the case where a standard  signal  is  already  pending,  the  siginfo_t
       structure  (see  sigaction(2))  associated with that signal is not overwritten on arrival of subsequent instances of the same signal.  Thus, the process will re‐
       ceive the information associated with the first instance of the signal.

   Signal numbering for standard signals
       The numeric value for each signal is given in the table below.  As shown in the table, many signals have different numeric  values  on  different  architectures.
       The  first  numeric value in each table row shows the signal number on x86, ARM, and most other architectures; the second value is for Alpha and SPARC; the third
       is for MIPS; and the last is for PARISC.  A dash (-) denotes that a signal is absent on the corresponding architecture.

       Signal        x86/ARM     Alpha/   MIPS   PARISC   Notes
                   most others   SPARC
       ─────────────────────────────────────────────────────────────────
       SIGHUP           1           1       1       1
       SIGINT           2           2       2       2
       SIGQUIT          3           3       3       3
       SIGILL           4           4       4       4
       SIGTRAP          5           5       5       5
       SIGABRT          6           6       6       6
       SIGIOT           6           6       6       6
       SIGBUS           7          10      10      10
       SIGEMT           -           7       7      -
       SIGFPE           8           8       8       8
       SIGKILL          9           9       9       9
       SIGUSR1         10          30      16      16
       SIGSEGV         11          11      11      11
       SIGUSR2         12          31      17      17
       SIGPIPE         13          13      13      13
       SIGALRM         14          14      14      14
       SIGTERM         15          15      15      15
       SIGSTKFLT       16          -       -        7
       SIGCHLD         17          20      18      18
       SIGCLD           -          -       18      -
       SIGCONT         18          19      25      26
       SIGSTOP         19          17      23      24
       SIGTSTP         20          18      24      25
       SIGTTIN         21          21      26      27
       SIGTTOU         22          22      27      28
       SIGURG          23          16      21      29
       SIGXCPU         24          24      30      12
       SIGXFSZ         25          25      31      30
       SIGVTALRM       26          26      28      20
       SIGPROF         27          27      29      21
       SIGWINCH        28          28      20      23

       SIGIO           29          23      22      22
       SIGPOLL                                            Same as SIGIO
       SIGPWR          30         29/-     19      19
       SIGINFO          -         29/-     -       -
       SIGLOST          -         -/29     -       -
       SIGSYS          31          12      12      31
       SIGUNUSED       31          -       -       31

       Note the following:

       *  Where defined, SIGUNUSED is synonymous with SIGSYS.  Since glibc 2.26, SIGUNUSED is no longer defined on any architecture.

       *  Signal 29 is SIGINFO/SIGPWR (synonyms for the same value) on Alpha but SIGLOST on SPARC.

   Real-time signals
       Starting with version 2.2, Linux supports real-time signals as originally defined in the POSIX.1b real-time extensions (and now included in  POSIX.1-2001).   The
       range  of  supported  real-time signals is defined by the macros SIGRTMIN and SIGRTMAX.  POSIX.1-2001 requires that an implementation support at least _POSIX_RT‐
       SIG_MAX (8) real-time signals.

       The Linux kernel supports a range of 33 different real-time signals, numbered 32 to 64.  However, the glibc POSIX threads implementation internally uses two (for
       NPTL)  or three (for LinuxThreads) real-time signals (see pthreads(7)), and adjusts the value of SIGRTMIN suitably (to 34 or 35).  Because the range of available
       real-time signals varies according to the glibc threading implementation (and this variation can occur at run time according to the available kernel and  glibc),
       and  indeed  the  range  of  real-time signals varies across UNIX systems, programs should never refer to real-time signals using hard-coded numbers, but instead
       should always refer to real-time signals using the notation SIGRTMIN+n, and include suitable (run-time) checks that SIGRTMIN+n does not exceed SIGRTMAX.

       Unlike standard signals, real-time signals have no predefined meanings: the entire set of real-time signals can be used for application-defined purposes.

       The default action for an unhandled real-time signal is to terminate the receiving process.

       Real-time signals are distinguished by the following:

       1.  Multiple instances of real-time signals can be queued.  By contrast, if multiple instances of a standard signal are delivered while that signal is  currently
           blocked, then only one instance is queued.

       2.  If the signal is sent using sigqueue(3), an accompanying value (either an integer or a pointer) can be sent with the signal.  If the receiving process estab‐
           lishes a handler for this signal using the SA_SIGINFO flag to sigaction(2), then it can obtain this data via the si_value field of  the  siginfo_t  structure
           passed  as the second argument to the handler.  Furthermore, the si_pid and si_uid fields of this structure can be used to obtain the PID and real user ID of
           the process sending the signal.

       3.  Real-time signals are delivered in a guaranteed order.  Multiple real-time signals of the same type are delivered in the order they were sent.  If  different
           real-time  signals  are  sent to a process, they are delivered starting with the lowest-numbered signal.  (I.e., low-numbered signals have highest priority.)
           By contrast, if multiple standard signals are pending for a process, the order in which they are delivered is unspecified.

       If both standard and real-time signals are pending for a process, POSIX leaves it unspecified which is delivered first.  Linux, like many other  implementations,
       gives priority to standard signals in this case.

       According  to  POSIX,  an implementation should permit at least _POSIX_SIGQUEUE_MAX (32) real-time signals to be queued to a process.  However, Linux does things
       differently.  In kernels up to and including 2.6.7, Linux imposes a system-wide limit on the number of queued real-time signals for all  processes.   This  limit
       can  be viewed and (with privilege) changed via the /proc/sys/kernel/rtsig-max file.  A related file, /proc/sys/kernel/rtsig-nr, can be used to find out how many
       real-time signals are currently queued.  In Linux 2.6.8, these /proc interfaces were replaced by the RLIMIT_SIGPENDING resource limit, which specifies a per-user
       limit for queued signals; see setrlimit(2) for further details.

       The  addition  of real-time signals required the widening of the signal set structure (sigset_t) from 32 to 64 bits.  Consequently, various system calls were su‐
       perseded by new system calls that supported the larger signal sets.  The old and new system calls are as follows:

       Linux 2.0 and earlier   Linux 2.2 and later
       sigaction(2)            rt_sigaction(2)
       sigpending(2)           rt_sigpending(2)
       sigprocmask(2)          rt_sigprocmask(2)
       sigreturn(2)            rt_sigreturn(2)
       sigsuspend(2)           rt_sigsuspend(2)
       sigtimedwait(2)         rt_sigtimedwait(2)

   Interruption of system calls and library functions by signal handlers
       If a signal handler is invoked while a system call or library function call is blocked, then either:

       * the call is automatically restarted after the signal handler returns; or

       * the call fails with the error EINTR.

       Which of these two behaviors occurs depends on the interface and whether or not the signal handler was established using the SA_RESTART flag (see  sigaction(2)).
       The details vary across UNIX systems; below, the details for Linux.

       If  a  blocked  call to one of the following interfaces is interrupted by a signal handler, then the call is automatically restarted after the signal handler re‐
       turns if the SA_RESTART flag was used; otherwise the call fails with the error EINTR:

       * read(2), readv(2), write(2), writev(2), and ioctl(2) calls on "slow" devices.  A "slow" device is one where the I/O call may block for an indefinite time,  for
         example,  a  terminal,  pipe,  or socket.  If an I/O call on a slow device has already transferred some data by the time it is interrupted by a signal handler,
         then the call will return a success status (normally, the number of bytes transferred).  Note that a (local) disk is not a slow device according to this  defi‐
         nition; I/O operations on disk devices are not interrupted by signals.

       * open(2), if it can block (e.g., when opening a FIFO; see fifo(7)).

       * wait(2), wait3(2), wait4(2), waitid(2), and waitpid(2).

       * Socket  interfaces:  accept(2), connect(2), recv(2), recvfrom(2), recvmmsg(2), recvmsg(2), send(2), sendto(2), and sendmsg(2), unless a timeout has been set on
         the socket (see below).

       * File locking interfaces: flock(2) and the F_SETLKW and F_OFD_SETLKW operations of fcntl(2)

       * POSIX message queue interfaces: mq_receive(3), mq_timedreceive(3), mq_send(3), and mq_timedsend(3).

       * futex(2) FUTEX_WAIT (since Linux 2.6.22; beforehand, always failed with EINTR).

       * getrandom(2).

       * pthread_mutex_lock(3), pthread_cond_wait(3), and related APIs.

       * futex(2) FUTEX_WAIT_BITSET.

       * POSIX semaphore interfaces: sem_wait(3) and sem_timedwait(3) (since Linux 2.6.22; beforehand, always failed with EINTR).

       * read(2) from an inotify(7) file descriptor (since Linux 3.8; beforehand, always failed with EINTR).

       The following interfaces are never restarted after being interrupted by a signal handler, regardless of the use of SA_RESTART; they always fail  with  the  error
       EINTR when interrupted by a signal handler:

       * "Input" socket interfaces, when a timeout (SO_RCVTIMEO) has been set on the socket using setsockopt(2): accept(2), recv(2), recvfrom(2), recvmmsg(2) (also with
         a non-NULL timeout argument), and recvmsg(2).

       * "Output" socket interfaces, when a timeout (SO_RCVTIMEO) has been set on the socket using setsockopt(2): connect(2), send(2), sendto(2), and sendmsg(2).

       * Interfaces used to wait for signals: pause(2), sigsuspend(2), sigtimedwait(2), and sigwaitinfo(2).

       * File descriptor multiplexing interfaces: epoll_wait(2), epoll_pwait(2), poll(2), ppoll(2), select(2), and pselect(2).

       * System V IPC interfaces: msgrcv(2), msgsnd(2), semop(2), and semtimedop(2).

       * Sleep interfaces: clock_nanosleep(2), nanosleep(2), and usleep(3).

       * io_getevents(2).

       The sleep(3) function is also never restarted if interrupted by a handler, but gives a success return: the number of seconds remaining to sleep.

       In certain circumstances, the seccomp(2) user-space notification feature can lead to restarting of system calls  that  would  otherwise  never  be  restarted  by
       SA_RESTART; for details, see seccomp_unotify(2).

   Interruption of system calls and library functions by stop signals
       On  Linux, even in the absence of signal handlers, certain blocking interfaces can fail with the error EINTR after the process is stopped by one of the stop sig‐
       nals and then resumed via SIGCONT.  This behavior is not sanctioned by POSIX.1, and doesn't occur on other systems.

       The Linux interfaces that display this behavior are:

       * "Input" socket interfaces, when a timeout (SO_RCVTIMEO) has been set on the socket using setsockopt(2): accept(2), recv(2), recvfrom(2), recvmmsg(2) (also with
         a non-NULL timeout argument), and recvmsg(2).

       * "Output"  socket  interfaces, when a timeout (SO_RCVTIMEO) has been set on the socket using setsockopt(2): connect(2), send(2), sendto(2), and sendmsg(2), if a
         send timeout (SO_SNDTIMEO) has been set.

       * epoll_wait(2), epoll_pwait(2).

       * semop(2), semtimedop(2).

       * sigtimedwait(2), sigwaitinfo(2).

       * Linux 3.7 and earlier: read(2) from an inotify(7) file descriptor

       * Linux 2.6.21 and earlier: futex(2) FUTEX_WAIT, sem_timedwait(3), sem_wait(3).

       * Linux 2.6.8 and earlier: msgrcv(2), msgsnd(2).

       * Linux 2.4 and earlier: nanosleep(2).

CONFORMING TO
       POSIX.1, except as noted.

NOTES
       For a discussion of async-signal-safe functions, see signal-safety(7).

       The /proc/[pid]/task/[tid]/status file contains various fields that show the signals that a thread is blocking (SigBlk), catching (SigCgt), or ignoring (SigIgn).
       (The set of signals that are caught or ignored will be the same across all threads in a process.)  Other fields show the set of pending signals that are directed
       to the thread (SigPnd) as well as the set of pending signals that are directed to the process as a whole (ShdPnd).  The corresponding fields in  /proc/[pid]/sta‐
       tus show the information for the main thread.  See proc(5) for further details.

BUGS
       There  are six signals that can be delivered as a consequence of a hardware exception: SIGBUS, SIGEMT, SIGFPE, SIGILL, SIGSEGV, and SIGTRAP.  Which of these sig‐
       nals is delivered, for any given hardware exception, is not documented and does not always make sense.

       For example, an invalid memory access that causes delivery of SIGSEGV on one CPU architecture may cause delivery of  SIGBUS  on  another  architecture,  or  vice
       versa.

       For  another  example,  using  the  x86 int instruction with a forbidden argument (any number other than 3 or 128) causes delivery of SIGSEGV, even though SIGILL
       would make more sense, because of how the CPU reports the forbidden operation to the kernel.

SEE ALSO
       kill(1), clone(2), getrlimit(2), kill(2), pidfd_send_signal(2), restart_syscall(2), rt_sigqueueinfo(2), setitimer(2),  setrlimit(2),  sgetmask(2),  sigaction(2),
       sigaltstack(2),  signal(2),  signalfd(2),  sigpending(2),  sigprocmask(2),  sigreturn(2),  sigsuspend(2),  sigwaitinfo(2),  abort(3),  bsd_signal(3),  killpg(3),
       longjmp(3), pthread_sigqueue(3), raise(3), sigqueue(3), sigset(3), sigsetops(3), sigvec(3), sigwait(3), strsignal(3),  swapcontext(3),  sysv_signal(3),  core(5),
       proc(5), nptl(7), pthreads(7), sigevent(7)

Linux                                                                          2021-03-22                                                                      SIGNAL(7)