bigrigg: CS1550 Summer 2005

bigrigg (

bigrigg) wrote,
@ 2005-05-07 09:24:00

CS1550 Summer 2005
Introduction to Operating Systems

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	bigrigg@cs.pitt.edu bigrigg 2005-05-07 01:54 pm UTC (link)
	Post anonymously, but use your email address for the subject field. This makes any required follow-up easier. (Reply to this)

	cms78@pitt.edu (Anonymous) 2005-05-20 03:12 pm UTC (link)
	OK... I've got the two c files in my unix "private" directory and I've successfully compiled them into "myshell". But I can't get the program to execute. When I type "myshell" at the prompt it just tells me "command not found." Having a major "duh" moment here, plz help :) (Reply to this)

	cms78@pitt.edu (Anonymous) 2005-05-20 03:21 pm UTC (link)
	NM I figured it out. That directory isn't in the PATH, so I have to type "./myshell" (Reply to this)

jon_conley@comcast.net
(Anonymous)
2005-05-22 03:56 pm UTC (link)

I am looking for a good way for a parent process to communicate with its child processes (in assignment 1). I know that the parent needs to find out the status of its children (Running, Terminated, etc.) but I'm not sure how to go about it. Parent can intercept SIGCHLD signals which will tell it if a child was terminated, but doesn't appear to be able to find out which child. Popen() will create a pipe between the parent and child, but it appears to only be able to read from the child's stdin or write to its stdout. Or am I barking up the wrong tree altogether?

(Reply to this) (Thread)

bigrigg@cs.pitt.edu

bigrigg
2005-05-22 05:16 pm UTC (link)

You say you want to communicate with the child. I assume you think that is how to "ask" it if it is still alive. Perhaps instead you want to ask the operating system. Look up waitpid. There is a version of it in the myshell.c code. Do a man on waitpid and look up how to ask the status of a process without hanging. If you can ask the status of processes based on their pid's, which is the value that you get back from fork. What kind of data structure are you going to use to keep track of the child processes that you spawn?

(Reply to this) (Parent)

	bigrigg@cs.pitt.edu bigrigg 2005-05-22 06:02 pm UTC (link)
	As mentioned possible in the last lecture, we will combine the Tue and Thur recitation into one. The one recitation will be held on Tuesday evenings. The first combined recitation will be this Tuesday May 24th, where you will have your first quiz! (Reply to this) (Thread)

	bwheeler@pitt.edu (Anonymous) 2005-05-23 03:04 am UTC (link)
	Does this mean we will be dropping to only 1 day of office hours, since your Tuesday set of office hours are durring the same time as Tuesday's recitation class? (Reply to this) (Parent)(Thread)

	cms78@pitt.edu (Anonymous) 2005-05-23 04:05 am UTC (link)
	myshell seems to compile and runs under Cygwin (making my life a lot easier). Still I'll make sure it runs on "real" unix before submitting. So... what does the -lfl compiler flag do? I could look through a zillion pages of man file, but I'm lazy. :) (Reply to this) (Thread)

	Re: cms78@pitt.edu bigrigg 2005-05-23 04:26 am UTC (link)
	The -l flag is to link in a library. In this case it means to link in the lex library. While running "lex lex.c" will produce lex.yy.c, there are still some additional routines needed. (Reply to this) (Parent)

	bigrigg@cs.pitt.edu bigrigg 2005-05-25 04:28 pm UTC (link)
	Your comment has been noted. (Reply to this) (Parent)

	bigrigg@cs.pitt.edu bigrigg 2005-05-28 05:15 pm UTC (link)
	I wouldn't expect more than 20 jobs. But if you make an array that supports 100 jobs that should be reasonable. Make it 100 jobs maximum. (Reply to this) (Parent)

	bwheeler@pitt.edu (Anonymous) 2005-05-28 06:59 pm UTC (link)
	On the programming assignment is says that jobs takes no arguments, timex takes an application for an argument, and all the other commands we are to implement take a job id number as an argument. However if wait just "holds until all jobs are done" like mentioned on the assignment page why does it need a job id number passed to it? (Reply to this) (Thread)

	bwheeler@pitt.edu (Anonymous) 2005-05-28 08:46 pm UTC (link)
	I am also confused on what you want the notify command to do. Is it suppost to block until the job sent through its argument is done? All of my internet searches are producing mixed results. (Reply to this) (Parent)(Thread)

	bigrigg@cs.pitt.edu bigrigg 2005-05-29 02:57 pm UTC (link)
	Sunday May 29th, 11AM. I will be gone for the rest of the day unable to respond to your emails. If you are stuck, leave a question here and perhaps a fellow classmate can answer. For those who can answer a question, it will help your class participation. (Reply to this)

	jjc31@pitt.edu (Anonymous) 2005-05-29 07:55 pm UTC (link)
	Hello I'm not sure what we need to do for most of these commands. I have jobs done but other than that .....?????? If someone can help point me in the right direction of what to do, it would be greatly appreciated. Thanks (Reply to this) (Thread)

	bwheeler@pitt.edu (Anonymous) 2005-05-29 08:10 pm UTC (link)
	My wait command has similar functionallity to my jobs command. I don't see how some of the rest of the commands can be done asynchronously without signals though. Anyone have any ideas about that? (Reply to this) (Parent)(Thread)

	mak78@pitt.edu (Anonymous) 2005-05-30 02:44 pm UTC (link)
	Does the STOP command means to pause the job ?? in the assignment it says to cancel the job ?? can anyone explain. (Reply to this) (Thread)

	bigrigg@cs.pitt.edu bigrigg 2005-05-30 04:33 pm UTC (link)
	From the man page (man stop)... stop: stops the execution of a background job(s) by using its job_id. You can say to cancel the job, to stop it, to kill it. To make it no longer around. It does not mean pause. The job is gone. (Reply to this) (Parent)(Thread)

	sarpeshk@hotmail.com (Anonymous) 2005-05-31 12:03 am UTC (link)
	Ok, I can't be the only one experiencing this...when I run ./myshell, I notice that any time I attempt to type backspace or delete at the prompt, it outputs an escape sequence instead of deleting the previous or following (or any) character. Is there any way to modify the shell to fix this annoying little behavior? (Reply to this) (Thread)

	Re: sarpeshk@hotmail.com (Anonymous) 2005-05-31 12:47 am UTC (link)
	Delete key works as Backspace key on mine!! (Reply to this) (Parent)(Thread)

	Project due date (Anonymous) 2005-05-31 12:39 am UTC (link)
	Do we e-mail the project midnight tonight or midnight tuesday night? (Reply to this) (Thread)

	bigrigg@cs.pitt.edu bigrigg 2005-05-31 01:18 am UTC (link)
	Please use your email address as the subject. Midnight Tuesday as in a few hours after class. Turn in the hardcopy of the program in lecture. (Reply to this) (Parent)

	Boi1@pitt.edu (Anonymous) 2005-05-31 02:11 am UTC (link)
	I think it would be very helpful to see a short demo of sending and handling signals. There is a lot of stuff about it in the man pages and it's all rather confusing. Also, if anyone has any recommanded simple tutorials on this, that would be great. (Reply to this)

	kad28@pitt.edu (Anonymous) 2005-05-31 02:13 am UTC (link)
	why is it that my 'wait' command works only once!!! it only works the first time that i type it in. if i type it again after i spawned some processes in the background, i'll get to the -> prompt!!!(it wont work anymore, unless i exit the shell, and open it again) I only used 'int result = wait(&status);' under the internal command. any help would be appreciated (Reply to this) (Thread)

	Re: kad28@pitt.edu (Anonymous) 2005-05-31 03:52 am UTC (link)
	Are you sure that wait is blocking? If you lunched it in the beginning, and there are no processes, it wouldn't block, and would return to you. But after you have processes, wait need to block and wait for them to finish. If it doesn't, it might still be running in the background, and looking for backgraound processes... (Reply to this) (Parent)(Thread)

	kad28@pitt.edu (Anonymous) 2005-05-31 03:12 am UTC (link)
	should we delete the jobs that are terminated, completed, from our job's array? Should we constantly update the array?? or can we just leave each processes' ID in the array, eventhough those processes dont exist any more? and just list whatever is in the array, except NULL, when the user types in 'jobs'? Thanks (Reply to this) (Thread)

	bigrigg@cs.pitt.edu bigrigg 2005-05-31 03:21 am UTC (link)
	You should probably delete the jobs from the array when they go away. There is no need to keep them around. (Reply to this) (Parent)

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	boi1@pitt.edu (Anonymous) 2005-05-31 01:15 pm UTC (link)
	Ok, silly question: How do I get the arguments out of the command line and into a useful format (IE put an argument into a variable)? the args array is decleared as char **args. what exactly does that mean? (Reply to this) (Thread)

	bigrigg@cs.pitt.edu bigrigg 2005-05-31 01:23 pm UTC (link)
	The line args=getline() will take the command line (what you type in at the -> prompt) and parse it into the individual words and store them into the args. The args is an array of strings. args[0] is the "command" and args[1] args[2] etc are the parameters given to the command. (Reply to this) (Parent)(Thread)

	sve2@pitt.edu (Anonymous) 2005-05-31 08:11 pm UTC (link)
	Does it matter if my internal commands use process id's as the job id and not a simplified number? (Reply to this) (Thread)

	sarpeshk@hotmail.com (Anonymous) 2005-06-01 02:40 am UTC (link)
	I exclusively used the actual process ID's. I honestly don't think it matters, as long as the functions worked properly under whichever system you used. (Reply to this) (Parent)

	kad28@pitt.edu (Anonymous) 2005-06-01 12:53 am UTC (link)
	i know that i have to use SIGCONT signal to continue a job. but how do i turn a suspended background job into a active foreground job?? and vise versa? is there acutally a difference in bg and fg coding? and where should i be looking for the timex command? the man command doesnt help me much. (Reply to this) (Thread)

	bigrigg@cs.pitt.edu bigrigg 2005-06-01 01:30 am UTC (link)
	SIGCONT to continue (resume a background job) and SIGSTOP to suspend (pause a background job). To put a job into the foreground means that you block until that job is done. As for timex, look up gettimeofday(). (Reply to this) (Parent)

	kad28@pitt.edu (Anonymous) 2005-06-02 07:50 pm UTC (link)
	should we make a report, printed hard copies, even if we were to demonstrate our late projects today(thursday after class)? Thx (Reply to this) (Thread)

	bigrigg@cs.pitt.edu bigrigg 2005-06-02 08:41 pm UTC (link)
	Not everyone will be able to demo this week. Late projects and the people we couldn't get to this week will demo next week. (Reply to this) (Parent)

	cms78@pitt.edu (Anonymous) 2005-06-03 02:56 pm UTC (link)
	Since we're in between projects, here's some bandwidth wastage for you all. Programming Languange Inventor or Serial Killer (http://www.malevole.com/mv/misc/killerquiz/) (Reply to this)

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