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Full Discussion: [KSH/Bash] Starting a parent process from a child process?
Top Forums Shell Programming and Scripting [KSH/Bash] Starting a parent process from a child process? Post 302408512 by alister on Monday 29th of March 2010 05:51:50 PM
Old 03-29-2010
The death of a process, even a parent process, does not trigger the kernel to send SIGHUP to any processes. That only happens when the controlling terminal/pseudo terminal is hung up/closed. If SIGHUP is not the signal being sent, nohup will not prevent a process dying if that is the default action for whatever signal it is actually being sent (a SIGINT or SIGTERM will still kill a process, unless they're explicitly trapped by the receiving process).

Default behavior when a SIGHUP signal is sent to a process is for the kernel to terminate the process. nohup simply sets the SIGHUP signal to be ignored and then execs its argument (the command you want to run, which then inherits this signal handling modification from nohup ... all other singal handling is unmodified).

The heart of OpenBSD's nohup implementation:
Code:
	/*
	 * The nohup utility shall take the standard action for all signals
	 * except that SIGHUP shall be ignored.
	 */
	(void)signal(SIGHUP, SIG_IGN);

	execvp(argv[1], &argv[1]);

from src/usr.bin/nohup/nohup.c - view - 1.14

Regards,
Alister
Last edited by alister; 03-29-2010 at 07:00 PM..
 

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LEARN ABOUT X11R4

nohup

NOHUP(1)							   User Commands							  NOHUP(1)

NAME

       nohup - run a command immune to hangups, with output to a non-tty

SYNOPSIS

       nohup COMMAND [ARG]...
       nohup OPTION

DESCRIPTION

       Run COMMAND, ignoring hangup signals.

       --help display this help and exit

       --version
	      output version information and exit

       If  standard  input  is a terminal, redirect it from an unreadable file.  If standard output is a terminal, append output to 'nohup.out' if
       possible, '$HOME/nohup.out' otherwise.  If standard error is a terminal, redirect it to standard output.   To  save  output  to	FILE,  use
       'nohup COMMAND > FILE'.

       NOTE: your shell may have its own version of nohup, which usually supersedes the version described here.  Please refer to your shell's doc-
       umentation for details about the options it supports.

AUTHOR

       Written by Jim Meyering.

REPORTING BUGS

       GNU coreutils online help: <http://www.gnu.org/software/coreutils/>
       Report nohup translation bugs to <http://translationproject.org/team/>

COPYRIGHT

       Copyright (C) 2017 Free Software Foundation, Inc.  License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>.
       This is free software: you are free to change and redistribute it.  There is NO WARRANTY, to the extent permitted by law.

SEE ALSO

       Full documentation at: <http://www.gnu.org/software/coreutils/nohup>
       or available locally via: info '(coreutils) nohup invocation'

GNU coreutils 8.28						   January 2018 							  NOHUP(1)
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