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Top Forums UNIX for Dummies Questions & Answers Return Codes... Post 302867345 by bakunin on Thursday 24th of October 2013 04:26:20 AM
Old 10-24-2013
Quote:
Originally Posted by wisecracker
This was just an idea...

I wasn't actually asking anything. I was experimenting with generating an error code
system of my own with values outside of an 8 bit range.
I used the real 255 exit code as 'number out of range' flag and then generate a string
whilst exit is in process. This string was originally a number, but I decided to make it
a string instead, purely for fun.
I am not sure if this will work in any way: return codes are not coming out of thin air, but the result of a system call, as jim mcNamara has explained. It can't give you back more than it ought to. It is defined as an unsigned 8-bit integer, so it can't deliver a 16- (or 32-, 64-, ...) bit number, a string or whatever. This would mean that this value has to be put on the stack and then pulled off it by the wait() or waitpid()-function. As the function would not know that it is expected to get that off the stack it won't do it and the stack would be (and stay) subsequently corrupted.

If you want to have extended exit-messages of any sort - strings, numbers, whatever - you will have to use the classical means of conveying such messages: interprocess communication (aka semaphores, shared memory segments, ... - take your pick) or process-to-process I/O, like file descriptors and/or named pipes. Write to <stdout>, <stderr>, etc. and intercept this with pipes, I/O-redirection and the like.

Another option is to write to a log file of some sort and have that parsed from the calling process.

Quote:
Originally Posted by wisecracker
Perhaps I shouldn't have posted it...
There is no harm done in discussing anything and i am convinced this board won't go down from 1k characters of non-conclusive discussion. Still, i think you should post such topics (and the likes - you seem to enjoy exploring the limits of the OS in general and the shell in specific) not in the beginner forum. This is clearly not the stuff someone who learned the shell yesterday asks first. Please consider moving to the experts forum for topics like this.

I hope this helps.

bakunin
This User Gave Thanks to bakunin For This Post:
 

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plock(2)							System Calls Manual							  plock(2)

NAME
plock() - lock process, text, data, stack, or shared library in memory SYNOPSIS
DESCRIPTION
The system call allows the calling process to lock the text segment of the process (text lock), its data segment (data lock), or both its text and data segment (process lock) into memory. Stack segments are also locked when data segments are locked. Shared library text and shared library data segments (shlib lock) can also be locked. Locked segments are immune to all routine swapping. also allows these seg- ments to be unlocked. The effective user ID of the calling process must be a user with the privilege. op must be one of the following: Lock text and data segments into memory (process lock) Lock text segment into memory (text lock) Lock data segment into memory (data lock) Remove locks Lock shared library text and shared library data segments (shared library lock) Lock text, data and shared library text and shared library data segments into memory (process and shared library lock) Lock text, shared library text and shared library data segments into memory (text and shared library lock) Lock data, shared library text and shared library data segments into memory (data and shared library lock) Although and the family of functions may be used together in an application, each may affect the other in unexpected ways. This practice is not recommended. Security Restrictions Some or all of the actions associated with this system call require the privilege. Processes owned by the superuser have this privilege. Processes owned by other users may have this privilege, depending on system configuration. See privileges(5) for more information about privileged access on systems that support fine-grained privileges. RETURN VALUE
returns the following values: Successful completion. Failure. The requested operation is not performed. is set to indicate the error. ERRORS
If fails, is set to one of the following values. op is equal to and a process lock, a text lock, or a data lock already exists on the calling process. op is equal to and a text lock or process lock already exists on the calling process. op is equal to and a data lock, or process lock already exists on the calling process. op is equal to and no type of lock exists on the calling process. op is equal to and there are no unlocked shared library segments in the calling process. op is equal to and a process lock, a text lock, or a data lock already exists on the calling process. op is equal to and a text lock or process lock already exists on the calling process. op is equal to and a data lock, or process lock already exists on the calling process. op is not equal to one of the values specified in is not allowed in a window. See vfork(2). There is not enough lockable memory in the system to satisfy the locking request. The effective user ID of the calling process is not a user with the privilege. EXAMPLES
The following call to locks the calling process in memory: SEE ALSO
setprivgrp(1M), exec(2), exit(2), fork(2), getprivgrp(2), mlock(2), vfork(2), privileges(5). STANDARDS CONFORMANCE
plock(2)
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