Unix Signal - Sending Signals

Sending Signals

  • Typing certain key combinations at the controlling terminal of a running process causes the system to send it certain signals:
    • Ctrl-C (in older Unixes, DEL) sends an INT signal (SIGINT); by default, this causes the process to terminate.
    • Ctrl-Z sends a TSTP signal (SIGTSTP); by default, this causes the process to suspend execution.
    • Ctrl-\ sends a QUIT signal (SIGQUIT); by default, this causes the process to terminate and dump core.
    • (Those default key combinations can be changed with the stty command.)
  • The kill(2) system call will send the specified signal to the process, if permissions allow. Similarly, the kill(1) command allows a user to send signals to processes. The raise(3) library function sends the specified signal to the current process.
  • Exceptions such as division by zero or a segmentation violation will generate signals (here, SIGFPE and SIGSEGV respectively, which both by default cause a core dump and a program exit).
  • The kernel can generate a signal to notify the process of an event. For example, SIGPIPE will be generated when a process writes to a pipe which has been closed by the reader; by default, this causes the process to terminate, which is convenient when constructing shell pipelines.

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