COMP3000 Operating Systems F23: Tutorial 3 - Revision history

Abdou: /* Tasks/Questions */

2023-10-09T14:46:42Z

Tasks/Questions

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	# Compared to [https://people.scs.carleton.ca/~abdou/comp3000/f23/tut1/csimpleshell.c csimpleshell] from Tutorial 1, what functionality improvements has 3000shell introduced? List at least two improvements (functional differences). Did you find them by reading the source code or trying both shells?		# Compared to [https://people.scs.carleton.ca/~abdou/comp3000/f23/tut1/csimpleshell.c csimpleshell] from Tutorial 1, what functionality improvements has 3000shell introduced? List at least two improvements (functional differences). Did you find them by reading the source code or trying both shells?
	# Pay attention to lines 229-235. How can you run a program in the background? Note: “in the background” means the shell starting a program without waiting for it to finish. So, the shell returns immediately to be ready to accept the next command.		# Pay attention to lines 229-235. How can you run a program in the background? Note: “in the background” means the shell starting a program without waiting for it to finish. So, the shell returns immediately to be ready to accept the next command.
	# Observe the behavior when running different programs in the background. What happens to the input and output of the program? Try this for different types of programs, such as <tt>ls</tt> and <tt>bc</tt>, or <tt>nano</tt> and <tt>top</tt>, or others of your choice. Write down your observations.		# Observe the behavior when running different programs in the background. What happens to the input and output of the program? Try this for different types of programs, such as <code>ls</code> and <code>bc</code>, or <code>nano</code> and <code>top</code>, or others of your choice. Write down your observations.
	# You may have trouble interacting with the shell after running programs in the background. How can you recover from such a situation? Note: you can do it in a harsh way for this question. We will see a smarter way next.		# You may have trouble interacting with the shell after running programs in the background. How can you recover from such a situation? Note: you can do it in a harsh way for this question. We will see a smarter way next.
	# 3000shell implements a simple form of output redirection (i.e., the standard output mentioned earlier). What syntax should you use to redirect standard output to a file?		# 3000shell implements a simple form of output redirection (i.e., the standard output mentioned earlier). What syntax should you use to redirect standard output to a file?
	# Make the shell output "Ouch!" when you send it a <tt>SIGUSR1</tt> signal.		# Make the shell output "Ouch!" when you send it a <code>SIGUSR1</code> signal.
	# If you delete line 324 (<tt>SA_RESTART</tt>), how does the behavior of 3000shell change?		# If you delete line 324 (<code>SA_RESTART</code>), how does the behavior of 3000shell change?
	# Replace the use of <tt>find_env()</tt> with <tt>getenv()</tt>. How do their interfaces differ?		# Replace the use of <code>find_env()</code> with <code>getenv()</code>. How do their interfaces differ?
	# Make <tt>plist</tt> output the parent process id for each process, e.g., "5123 ls (5122)". Pay attention to the <tt>stat</tt> and <tt>status</tt> files in the per-process directories in <tt>/proc</tt>.		# Make <code>plist</code> output the parent process id for each process, e.g., "5123 ls (5122)". Pay attention to the <code>stat</code> and <code>status</code> files in the per-process directories in <code>/proc</code>.
	# If the shell gets stuck as a result of running a program in the background, how can you recover elegantly (resuming it) by sending just a signal (which signal)? <u>Why?</u>		# If the shell gets stuck as a result of running a program in the background, how can you recover elegantly (resuming it) by sending just a signal (which signal)? <u>Why?</u>

Abdou: /* Tasks/Questions */

2023-10-09T14:44:31Z

Tasks/Questions

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	# Compile and run [https://people.scs.carleton.ca/~abdou/comp3000/f23/tut3/3000shell.c 3000shell.c].		# Compile and run [https://people.scs.carleton.ca/~abdou/comp3000/f23/tut3/3000shell.c 3000shell.c].
	# Compared to [https://people.scs.carleton.ca/~abdou/comp3000/f23/tut1/csimpleshell.c csimpleshell] from Tutorial 1, what functionality improvements has 3000shell introduced? List at least two improvements (functional differences). ~~You can mention whether~~ you ~~found~~ them by reading the source code or trying both shells.		# Compared to [https://people.scs.carleton.ca/~abdou/comp3000/f23/tut1/csimpleshell.c csimpleshell] from Tutorial 1, what functionality improvements has 3000shell introduced? List at least two improvements (functional differences). Did you find them by reading the source code or trying both shells?
	# Pay attention to lines 229-235. How can you run a program in the background? Note: “in the background” means the shell starting a program without waiting for it to finish. So, the shell returns immediately to be ready to accept the next command.		# Pay attention to lines 229-235. How can you run a program in the background? Note: “in the background” means the shell starting a program without waiting for it to finish. So, the shell returns immediately to be ready to accept the next command.
	# Observe the behavior when running different programs in the background. What happens to the input and output of the program? Try this for different types of programs, such as <tt>ls</tt> and <tt>bc</tt>, or <tt>nano</tt> and <tt>top</tt>, or others of your choice. Write down your observations.		# Observe the behavior when running different programs in the background. What happens to the input and output of the program? Try this for different types of programs, such as <tt>ls</tt> and <tt>bc</tt>, or <tt>nano</tt> and <tt>top</tt>, or others of your choice. Write down your observations.

Abdou: /* Tasks/Questions */

2023-10-09T14:43:53Z

Tasks/Questions

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	==Tasks/Questions==		==Tasks/Questions==
	The purpose of the following questions and tasks is to help you understand how 3000shell (a simple implementation of the shell, but still more complex than the previous <tt>csimpleshell</tt>) works. Eventually, you should have an understanding of every function and every line of the code. If you understand 3000shell, then you understand the basics of all Linux/UNIX shells. Your understanding of the code will be tested later, so use this opportunity to dive deep into the code.		The purpose of the following questions and tasks is to help you understand how 3000shell (a simple implementation of the shell, but still more complex than the previous <tt>csimpleshell</tt>) works. Eventually, you should have an understanding of every function and every line of the code. If you understand 3000shell, then you understand the basics of all Linux/UNIX shells. Your understanding of the code will be tested later, so use this opportunity to dive deep into the code.

	~~You do not need to submit a separate file for source code changes. Just describe your changes or paste the code snippet (usually a few lines at the most).~~

	# Compile and run [https://people.scs.carleton.ca/~abdou/comp3000/f23/tut3/3000shell.c 3000shell.c].		# Compile and run [https://people.scs.carleton.ca/~abdou/comp3000/f23/tut3/3000shell.c 3000shell.c].

Abdou: /* Standard input/output, Shell and Terminal */

2023-10-09T14:36:18Z

Standard input/output, Shell and Terminal

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	ps -ef \| grep 3000shell #to look for the 3000shell process from the process list		ps -ef \| grep 3000shell #to look for the 3000shell process from the process list

	gcc -O2 -o csimpleshell csimpleshell.c 2>err.txt #to redirect error messages to a file err.txt		gcc -O2 -o csimpleshell csimpleshell.c 2 > err.txt #to redirect error messages to a file err.txt

	Later in the term if you find your disk space filled up, you can use the following command to pinpoint the top 20 largest files (no need to understand the specifics unless you are curious):		Later in the term if you find your disk space filled up, you can use the following command to pinpoint the top 20 largest files (no need to understand the specifics unless you are curious):

Abdou: /* Standard input/output, Shell and Terminal */

2023-10-09T14:35:35Z

Standard input/output, Shell and Terminal

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	===Standard input/output, Shell and Terminal===		===Standard input/output, Shell and Terminal===
	Recall that the shell is a command interpreter (program). In comparison, a terminal is a device used to enter data into and display/printing data from a computer. It used to be physical - [https://en.wikipedia.org/wiki/Teleprinter teletypes, or "TTY"'s], but today we mostly use virtual teminals, saving the need for the physical form but providing the same interface (another loose example of virtualization). There is a special virtual terminal mechanism in Linux/UNIX referred to as pts -- pseudo teletypes, e.g., <tt>/dev/pts/1</tt> (~~they are just the slave side. Those who are curious can refer to~~ <tt>man ptmx</tt>, ~~but~~ not needed in this tutorial).		Recall that the shell is a command interpreter (program). In comparison, a terminal is a device used to enter data into and display/printing data from a computer. It used to be physical - [https://en.wikipedia.org/wiki/Teleprinter teletypes, or "TTY"'s], but today we mostly use virtual teminals, saving the need for the physical form but providing the same interface (another loose example of virtualization). There is a special virtual terminal mechanism in Linux/UNIX referred to as <code>pts</code> -- pseudo teletypes, e.g., <code>/dev/pts/1</code> (check-out <code>man ptmx</code> if you are curious, though this is not needed in this tutorial).

	The standard input (e.g., <tt>/dev/stdin</tt>), output (e.g., <tt>/dev/stdout</tt>) and error (<tt>/dev/stderr</tt>) are just symbolic endpoints in any programs (of which the shell is an example), that can be redirected anywhere, where output goes, input comes and error is reported. By default, they refer to file descriptors 0, 1, and 2 for the current process.		The standard input (e.g., <code>/dev/stdin</code>), output (e.g., <code>/dev/stdout</code>) and error (<code>/dev/stderr</code>) are just symbolic endpoints in any programs (of which the shell is an example), that can be redirected anywhere, where output goes, input comes and error is reported. By default, they refer to file descriptors 0, 1, and 2 for the current process.

	<u>So, in summary, you connect to a terminal to interact with a computer, by running a shell to receive your commands, which redirects standard in/out/err to the terminal.</u>		<u>So, in summary, you connect to a terminal to interact with a computer, by running a shell to receive your commands, which redirects standard in/out/err to the terminal.</u>

Abdou: /* Standard input/output, Shell and Terminal */

2023-10-09T14:32:43Z

Standard input/output, Shell and Terminal

← Older revision		Revision as of 14:32, 9 October 2023
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	===Standard input/output, Shell and Terminal===		===Standard input/output, Shell and Terminal===
	Recall that the shell is a command interpreter (program). In comparison, a terminal is a device used to enter data into and display/printing data from a computer. It used to be physical - [https://en.wikipedia.org/wiki/Teleprinter teletypes, or "TTY"'s], but today we mostly use virtual teminals, saving the need for the physical form but providing the same interface (~~recall~~ virtualization). There is a special virtual terminal mechanism in Linux/UNIX referred to as pts -- pseudo teletypes, e.g., <tt>/dev/pts/1</tt> (they are just the slave side. Those who are curious can refer to <tt>man ptmx</tt>, but not needed in this tutorial).		Recall that the shell is a command interpreter (program). In comparison, a terminal is a device used to enter data into and display/printing data from a computer. It used to be physical - [https://en.wikipedia.org/wiki/Teleprinter teletypes, or "TTY"'s], but today we mostly use virtual teminals, saving the need for the physical form but providing the same interface (another loose example of virtualization). There is a special virtual terminal mechanism in Linux/UNIX referred to as pts -- pseudo teletypes, e.g., <tt>/dev/pts/1</tt> (they are just the slave side. Those who are curious can refer to <tt>man ptmx</tt>, but not needed in this tutorial).

	The standard input (e.g., <tt>/dev/stdin</tt>), output (e.g., <tt>/dev/stdout</tt>) and error (<tt>/dev/stderr</tt>) are just symbolic endpoints in any programs (of which the shell is an example), that can be redirected anywhere, where output goes, input comes and error is reported. By default, they refer to file descriptors 0, 1, and 2 for the current process.		The standard input (e.g., <tt>/dev/stdin</tt>), output (e.g., <tt>/dev/stdout</tt>) and error (<tt>/dev/stderr</tt>) are just symbolic endpoints in any programs (of which the shell is an example), that can be redirected anywhere, where output goes, input comes and error is reported. By default, they refer to file descriptors 0, 1, and 2 for the current process.

Abdou: /* Background */

2023-10-09T13:57:17Z

Background

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	==Background==		==Background==
	===Processes===		===Processes===
	Each application running on a system is assigned a unique process identifier (PID). The <tt>ps</tt> command shows the process identifiers for running processes. Each process running on the system is kept separated from other processes by the operating system.		Each application running on a system is assigned a unique process identifier (PID). The <code>ps</code> command shows the process identifiers for running processes. Each process running on the system is kept separated from other processes by the operating system.

	When you enter a command at a shell prompt, most of the time you are creating a new process which runs the program you specified.		When you enter a command at a shell prompt, most of the time you are creating a new process which runs the program you specified.

Abdou: /* Tasks/Questions */

2023-10-09T13:49:24Z

Tasks/Questions

← Older revision		Revision as of 13:49, 9 October 2023
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	You do not need to submit a separate file for source code changes. Just describe your changes or paste the code snippet (usually a few lines at the most).		You do not need to submit a separate file for source code changes. Just describe your changes or paste the code snippet (usually a few lines at the most).

	# Compile and run [https://people.scs.carleton.ca/~~~lianyingzhao~~/comp3000/~~w23~~/tut3/3000shell.c 3000shell.c].		# Compile and run [https://people.scs.carleton.ca/~abdou/comp3000/f23/tut3/3000shell.c 3000shell.c].
	# Compared to [https://people.scs.carleton.ca/~~~lianyingzhao~~/comp3000/~~w23~~/tut1/csimpleshell.c csimpleshell] from Tutorial 1, what functionality improvements has 3000shell introduced? List at least two improvements (functional differences). You can mention whether you found them by reading the source code or trying both shells.		# Compared to [https://people.scs.carleton.ca/~abdou/comp3000/f23/tut1/csimpleshell.c csimpleshell] from Tutorial 1, what functionality improvements has 3000shell introduced? List at least two improvements (functional differences). You can mention whether you found them by reading the source code or trying both shells.
	# Pay attention to lines 229-235. How can you run a program in the background? Note: “in the background” means the shell starting a program without waiting for it to finish. So, the shell returns immediately to be ready to accept the next command.		# Pay attention to lines 229-235. How can you run a program in the background? Note: “in the background” means the shell starting a program without waiting for it to finish. So, the shell returns immediately to be ready to accept the next command.
	# Observe the behavior when running different programs in the background. What happens to the input and output of the program? Try this for different types of programs, such as <tt>ls</tt> and <tt>bc</tt>, or <tt>nano</tt> and <tt>top</tt>, or others of your choice. Write down your observations.		# Observe the behavior when running different programs in the background. What happens to the input and output of the program? Try this for different types of programs, such as <tt>ls</tt> and <tt>bc</tt>, or <tt>nano</tt> and <tt>top</tt>, or others of your choice. Write down your observations.

Abdou at 13:48, 9 October 2023

2023-10-09T13:48:35Z

← Older revision		Revision as of 13:48, 9 October 2023
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	In this tutorial, you will be experimenting with and extending [https://people.scs.carleton.ca/~abdou/comp3000/f23/tut3/3000shell.c 3000shell.c], a proof-of-concept program to show you how a Linux shell works. Also, you will be learning to read and modify C code, which prepares you for subsequent tutorials and assignments.		In this tutorial, you will be experimenting with and extending [https://people.scs.carleton.ca/~abdou/comp3000/f23/tut3/3000shell.c 3000shell.c], a proof-of-concept program to show you how a Linux shell works. Also, you will be learning to read and modify C code, which prepares you for subsequent tutorials and assignments.

	~~==General Instructions (same for all tutorials)==~~

	~~<div class="mw-collapsible mw-collapsed">~~
	~~Click on Expand to view.~~
	~~<div class="mw-collapsible-content">~~
	Tutorials are graded based on participation and effort ('''so no need to struggle to have the “correct” answers — what matters is the attempts and sufficient thinking reflected in your answers'''), but you should still turn in your work. Submit your answers on Brightspace as a single text file named "<username>-comp3000-t<n>.txt" (where username is your MyCarletonOne username and n is the tutorial number). The first four lines of this file should be "COMP 3000 Tutorial <n>", your name, student number, and the date of submission. Your submitted answers must at least respond to all the items in the '''Tasks/Questions''' section.

	The deadline is usually four days after the tutorial date (see the actual deadline on the submission entry). Note that the submission entry is enforced by the system, so you may fail to get the effort marks even if it is one minute past the deadline.

	You should also check in with your assigned TA (in person or by responding to a poll if online). Your TA will be your first point of contact when you have questions or encounter any issues during the tutorial session.

	~~You get 1.5 marks for submitting answers that shows your effort and 0.5 for checking in, making this tutorial worth 2 points total.~~

	~~Read through the instructions before starting your work to get an overall picture. When source files are needed, you can download them by clicking on the hyperlink.~~
	~~</div>~~
	~~</div>~~

	==Background==		==Background==

Abdou at 13:47, 9 October 2023

2023-10-09T13:47:09Z

← Older revision		Revision as of 13:47, 9 October 2023
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	In this tutorial, you will be experimenting with and extending [https://people.scs.carleton.ca/~~~lianyingzhao~~/comp3000/~~w23~~/tut3/3000shell.c 3000shell.c], a proof-of-concept program to show you how a Linux shell works. Also, you will be learning to read and modify C code, which prepares you for subsequent tutorials and assignments.		In this tutorial, you will be experimenting with and extending [https://people.scs.carleton.ca/~abdou/comp3000/f23/tut3/3000shell.c 3000shell.c], a proof-of-concept program to show you how a Linux shell works. Also, you will be learning to read and modify C code, which prepares you for subsequent tutorials and assignments.

	==General Instructions (same for all tutorials)==		==General Instructions (same for all tutorials)==