![]() ![]() SIGSEGV The SIGSEGV signal is sent to a process when it makes an invalid virtual memory reference, or segmentation fault, i.e. SIGQUIT The SIGQUIT signal is sent to a process by its controlling terminal when the user requests that the process quit and perform a core dump. SIGRTMIN to SIGRTMAX The SIGRTMIN to SIGRTMAX signals are intended to be used for user-defined purposes. It provides an alternative to active polling. Using it effectively leads to making asynchronous I/O requests since the kernel will poll the descriptor in place of the caller. ![]() SIGPOLL The SIGPOLL signal is sent when an event occurred on an explicitly watched file descriptor. SIGPIPE The SIGPIPE signal is sent to a process when it attempts to write to a pipe without a process connected to the other end. In contrast to SIGTERM and SIGINT, this signal cannot be caught or ignored, and the receiving process cannot perform any clean-up upon receiving this signal. SIGKILL The SIGKILL signal is sent to a process to cause it to terminate immediately ( kill). This is typically initiated by pressing Ctrl-C, but on some systems, the " delete" character or " break" key can be used. SIGINT The SIGINT signal is sent to a process by its controlling terminal when a user wishes to interrupt the process. SIGILL The SIGILL signal is sent to a process when it attempts to execute an illegal, malformed, unknown, or privileged instruction. nohup is a command to make a command ignore the signal. Many daemons will reload their configuration files and reopen their logfiles instead of exiting when receiving this signal. In modern systems, this signal usually means that the controlling pseudo or virtual terminal has been closed. It was originally designed to notify the process of a serial line drop (a hangup). SIGHUP The SIGHUP signal is sent to a process when its controlling terminal is closed. SIGFPE The SIGFPE signal is sent to a process when it executes an erroneous arithmetic operation, such as division by zero (the name "FPE", standing for floating-point exception, is a misnomer as the signal covers integer-arithmetic errors as well). One important use of this signal is in job control in the Unix shell. SIGCONT The SIGCONT signal instructs the operating system to continue (restart) a process previously paused by the SIGSTOP or SIGTSTP signal. One common usage of the signal is to instruct the operating system to clean up the resources used by a child process after its termination without an explicit call to the wait system call. SIGCHLD The SIGCHLD signal is sent to a process when a child process terminates, is interrupted, or resumes after being interrupted. The conditions that lead to the signal being sent are, for example, incorrect memory access alignment or non-existent physical address. SIGBUS The SIGBUS signal is sent to a process when it causes a bus error. SIGPROF is sent when CPU time used by the process and by the system on behalf of the process elapses. ![]() SIGVTALRM is sent when CPU time used by the process elapses. SIGALRM is sent when real or clock time elapses. SIGALRM, SIGVTALRM and SIGPROF The SIGALRM, SIGVTALRM and SIGPROF signal is sent to a process when the time limit specified in a call to a preceding alarm setting function (such as setitimer) elapses. The signal is usually initiated by the process itself when it calls abort function of the C Standard Library, but it can be sent to the process from outside like any other signal. POSIX signals SIGABRT The SIGABRT signal is sent to a process to tell it to abort, i.e. SIGTTOU 22,22,27 Stop Terminal output for background process SIGTTIN 21,21,26 Stop Terminal input for background process SIGTSTP 18,20,24 Stop Stop typed at terminal SIGCONT 19,18,25 Cont Continue if stopped SIGCHLD 20,17,18 Ign Child stopped or terminated SIGUSR2 31,12,17 Term User-defined signal 2 SIGUSR1 30,10,16 Term User-defined signal 1 SIGALRM 14 Term Timer signal from alarm(2) SIGTERM 15 Term Termination signal SIGPIPE 13 Term Broken pipe: write to pipe with no SIGABRT 6 Core Abort signal from abort(3) SIGFPE 8 Core Floating point exception SIGHUP 1 Term Hangup detected on controlling terminal Linux supports both POSIX reliable signals (hereinafter "standardįirst the signals described in the original POSIX.1-1990 standard. ![]()
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