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Top Forums UNIX for Dummies Questions & Answers what's the difference between signal and semaphore? Post 302524101 by Chirel on Saturday 21st of May 2011 01:29:22 PM
Old 05-21-2011
Right, no data buffers for signal, it's used to tell something coded by a number to a running process.

You can send a running process a signal, it's for example the work done by the kill command.
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KILL(1) 						    BSD General Commands Manual 						   KILL(1)

NAME
kill -- terminate or signal a process SYNOPSIS
kill [-s signal_name] pid ... kill -l [exit_status] kill -signal_name pid ... kill -signal_number pid ... DESCRIPTION
The kill utility sends a signal to the process(es) specified by the pid operand(s). Only the super-user may send signals to other users' processes. The options are as follows: -s signal_name A symbolic signal name specifying the signal to be sent instead of the default TERM. -l [exit_status] Display the name of the signal corresponding to exit_status. exit_status may be the exit status of a command killed by a signal (see the special sh(1) parameter '?') or a signal number. If no operand is given, display the names of all the signals. -signal_name A symbolic signal name specifying the signal to be sent instead of the default TERM. -signal_number A non-negative decimal integer, specifying the signal to be sent instead of the default TERM. The following pids have special meanings: -1 If superuser, broadcast the signal to all processes; otherwise broadcast to all processes belonging to the user. 0 Broadcast the signal to all processes in the current process group belonging to the user. Some of the more commonly used signals: 1 HUP (hang up) 2 INT (interrupt) 3 QUIT (quit) 6 ABRT (abort) 9 KILL (non-catchable, non-ignorable kill) 14 ALRM (alarm clock) 15 TERM (software termination signal) kill is a built-in to csh(1); it allows job specifiers of the form ``%...'' as arguments so process id's are not as often used as kill argu- ments. See csh(1) for details. SEE ALSO
csh(1), pgrep(1), pkill(1), ps(1), kill(2), sigaction(2), signal(7) STANDARDS
The kill function is expected to be IEEE Std 1003.2 (``POSIX.2'') compatible. HISTORY
A kill command appeared in Version 6 AT&T UNIX. BSD
April 28, 1995 BSD
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