Strange Ctrl+C behavior Post: 302997359

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Top Forums Shell Programming and Scripting Strange Ctrl+C behavior Post 302997359 by bakunin on Friday 12th of May 2017 03:24:21 AM

05-12-2017

Registered User

Quote:

Originally Posted by JackK

I forgot to tell that "nohup my_script.sh..." is executed inside parent shell script, which was used to prepare my_script.sh
Does this change anything? Smilie

As it is i already suspected that, so: no, that doesn't change anything.

It is like this: when you start a login shell a "terminal" is created (by a process called getty or something analogous). This terminal is part of the process environment of your login session and is then "inherited" thoughout the process tree originating in your login session. That is, whatever you start from there - foreground processes, background processes, ... - will always use this terminal for any (not-redirected) output. As soon as this terminal ceases to exist (i.e. you log off) all the other processes using this terminal too will also be terminated, because they too lose their terminal.

Now, you might want to have processes continue to run without your session remaining - in fact, this is what most applications are supposed to do: they should continue to run even if the session where they are started ends. One needs a way of telling a process that "yes, there is a terminal, but don't care if it goes away".

For exactly this purpose there is nohup ("no termination on hangup") and this is what it does. Still: this only works if the program honours it (that is: there needs to be some part in the code dealing with it) and second: it doesn't matter if the process is started froma script or by hand: this influences only where in the process tree it is located. Since the purpose of nohup is solely to "disown" the process it doesn't matter how it would otherwise inherit something (the terminal) it now won't.

I hope this explains it.

bakunin

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LEARN ABOUT NETBSD

tcsetpgrp

TCSETPGRP(3)						   BSD Library Functions Manual 					      TCSETPGRP(3)

NAME

     tcsetpgrp -- set foreground process group ID

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

     #include <unistd.h>

     int
     tcsetpgrp(int fd, pid_t pgrp_id);

DESCRIPTION

     If the process has a controlling terminal, the tcsetpgrp function sets the foreground process group ID associated with the terminal device to
     pgrp_id.  The terminal device associated with fd must be the controlling terminal of the calling process and the controlling terminal must be
     currently associated with the session of the calling process.  The value of pgrp_id must be the same as the process group ID of a process in
     the same session as the calling process.

     Upon successful completion, tcsetpgrp returns a value of zero.

ERRORS

     If an error occurs, tcgetpgrp returns -1 and the global variable errno is set to indicate the error, as follows:

     [EBADF]		The fd argument is not a valid file descriptor.

     [EINVAL]		An invalid value of pgrp_id was specified.

     [ENOTTY]		The calling process does not have a controlling terminal, or the file represented by fd is not the controlling terminal,
			or the controlling terminal is no longer associated with the session of the calling process.

     [EPERM]		The pgrp_id argument does not match the process group ID of a process in the same session as the calling process.

SEE ALSO

     setpgid(2), setsid(2), tcgetpgrp(3)

STANDARDS

     The tcsetpgprp function conforms to ISO/IEC 9945-1:1990 (``POSIX.1'').

BSD
								   June 4, 1993 							       BSD