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Full Discussion: Strange Ctrl+C behavior
Top Forums Shell Programming and Scripting Strange Ctrl+C behavior Post 302997359 by bakunin on Friday 12th of May 2017 03:24:21 AM
Old 05-12-2017
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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exit(1)                                                            User Commands                                                           exit(1)

NAME
exit, return, goto - shell built-in functions to enable the execution of the shell to advance beyond its sequence of steps SYNOPSIS
sh exit [n] return [n] csh exit [ ( expr )] goto label ksh *exit [n] *return [n] DESCRIPTION
sh exit will cause the calling shell or shell script to exit with the exit status specified by n. If n is omitted the exit status is that of the last command executed (an EOF will also cause the shell to exit.) return causes a function to exit with the return value specified by n. If n is omitted, the return status is that of the last command exe- cuted. csh exit will cause the calling shell or shell script to exit, either with the value of the status variable or with the value specified by the expression expr. The goto built-in uses a specified label as a search string amongst commands. The shell rewinds its input as much as possible and searches for a line of the form label: possibly preceded by space or tab characters. Execution continues after the indicated line. It is an error to jump to a label that occurs between a while or for built-in command and its corresponding end. ksh exit will cause the calling shell or shell script to exit with the exit status specified by n. The value will be the least significant 8 bits of the specified status. If n is omitted then the exit status is that of the last command executed. When exit occurs when executing a trap, the last command refers to the command that executed before the trap was invoked. An end-of-file will also cause the shell to exit except for a shell which has the ignoreeof option (See set below) turned on. return causes a shell function or '.' script to return to the invoking script with the return status specified by n. The value will be the least significant 8 bits of the specified status. If n is omitted then the return status is that of the last command executed. If return is invoked while not in a function or a '.' script, then it is the same as an exit. On this man page, ksh(1) commands that are preceded by one or two * (asterisks) are treated specially in the following ways: 1. Variable assignment lists preceding the command remain in effect when the command completes. 2. I/O redirections are processed after variable assignments. 3. Errors cause a script that contains them to abort. 4. Words, following a command preceded by ** that are in the format of a variable assignment, are expanded with the same rules as a vari- able assignment. This means that tilde substitution is performed after the = sign and word splitting and file name generation are not performed. ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | |Availability |SUNWcsu | +-----------------------------+-----------------------------+ SEE ALSO
break(1), csh(1), ksh(1), sh(1), attributes(5) SunOS 5.10 15 Apr 1994 exit(1)
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