COMP 3000 2012 Midterm Material - Revision history

Soma at 20:14, 25 October 2012

2012-10-25T20:14:22Z

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			Note the midterm will be in our regular classroom, 342 TB.

	==Sample Test Questions==		==Sample Test Questions==

Soma at 19:34, 24 October 2012

2012-10-24T19:34:36Z

Show changes

Soma: /* Sample Test Questions */

2012-10-24T15:28:51Z

Sample Test Questions

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	# What allocates the storage for environment variables and command-line arguments?		# What allocates the storage for environment variables and command-line arguments?
	# A file that has a logical size of one gigabyte but only takes up 100K on disk is called what kind of file in UNIX?		# A file that has a logical size of one gigabyte but only takes up 100K on disk is called what kind of file in UNIX?
			# What is an easy (but not foolproof way) way to tell that you are running in a virtual environment on Linux? What command do you run to get this information?
			# What is the purpose of the PATH environment variable?
			# When would you expect ltrace to output more lines than strace? When should strace output more than ltrace?
			# What command is used to change the priority of a process?
			# What is the difference between a library call and a function call?

	==Lab Questions==		==Lab Questions==

Soma: /* Sample Test Questions */

2012-10-24T14:57:31Z

Sample Test Questions

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	# In UNIX, there are three permissions associated with the user, the user's group, and everyone else. What are those three permissions?		# In UNIX, there are three permissions associated with the user, the user's group, and everyone else. What are those three permissions?
	# If you see a zombie process during normal system operation, how can you get rid of it?		# If you see a zombie process during normal system operation, how can you get rid of it?
	# I can copy a file using I/O redirection as follows: <tt>cat		# I can copy a file using I/O redirection as follows: <tt>cat /bin/ls > bar</tt>. If I now type <tt> ./bar</tt>, it won't run. However, if I run another command before typing <tt>./bar</tt>, I will get a file listing. What needed to be changed to get <tt>bar</tt> to run?
	/bin/ls > bar</tt>. If I now type <tt> ./bar</tt>, it won't run. However, if I run another command before typing <tt>./bar</tt>, I will get a file listing. What needed to be changed to get <tt>bar</tt> to run?
	# System calls cannot normally be made using standard function calls. What CPU mechanism is used by regular processes to invoke kernel functionality?		# System calls cannot normally be made using standard function calls. What CPU mechanism is used by regular processes to invoke kernel functionality?
	# After a fork system call, what runs first, the child process runs or the parent process?		# After a fork system call, what runs first, the child process runs or the parent process?
	# Signal handlers can be called at almost any point in a process's execution. (T/F)		# Signal handlers can be called at almost any point in a process's execution. (T/F)
	# System V init scripts run programs sequentially or in		# System V init scripts run programs sequentially or in parallel?
	parallel?
	# Without errors, what does the execve system call return? # Who calls a signal handler?		# Without errors, what does the execve system call return? # Who calls a signal handler?
	# What program is used to check the consistency of the data structures of a filesystem?		# What program is used to check the consistency of the data structures of a filesystem?

Soma: /* Sample Test Questions */

2012-10-24T14:57:13Z

Sample Test Questions

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	==Sample Test Questions==		==Sample Test Questions==

			# You can create a sparse file in UNIX by writing sequences of zeros to a file.
			# Are environment variables ``global'' variables? Specifically, if you change the value of an environment variable X in one process, what happens to the value of X in other processes?
			# In UNIX, there are three permissions associated with the user, the user's group, and everyone else. What are those three permissions?
			# If you see a zombie process during normal system operation, how can you get rid of it?
			# I can copy a file using I/O redirection as follows: <tt>cat
			/bin/ls > bar</tt>. If I now type <tt> ./bar</tt>, it won't run. However, if I run another command before typing <tt>./bar</tt>, I will get a file listing. What needed to be changed to get <tt>bar</tt> to run?
			# System calls cannot normally be made using standard function calls. What CPU mechanism is used by regular processes to invoke kernel functionality?
			# After a fork system call, what runs first, the child process runs or the parent process?
			# Signal handlers can be called at almost any point in a process's execution. (T/F)
			# System V init scripts run programs sequentially or in
			parallel?
			# Without errors, what does the execve system call return? # Who calls a signal handler?
			# What program is used to check the consistency of the data structures of a filesystem?
			# What allocates the storage for environment variables and command-line arguments?
			# A file that has a logical size of one gigabyte but only takes up 100K on disk is called what kind of file in UNIX?

	==Lab Questions==		==Lab Questions==

Soma at 14:21, 24 October 2012

2012-10-24T14:21:38Z

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	== Questions ==		==Sample Test Questions==

			==Lab Questions==

	Questions from Lab 1		Questions from Lab 1

Sdp: added answers from lab 2

2012-10-22T22:08:49Z

added answers from lab 2

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	That is, the new process gets its own copy of these variables, which it can read, modify, and pass on in turn to its own children. In fact, every UNIX process (not just the shell) passes its environment variables to its child processes.</li>		That is, the new process gets its own copy of these variables, which it can read, modify, and pass on in turn to its own children. In fact, every UNIX process (not just the shell) passes its environment variables to its child processes.</li>
	</ol>		</ol>

			Answers from Lab 2

			# ps -aux<br/>ps -e<br/>Among others.
			# cron - Cron is the time-based job scheduler.<br/>lightdm - Display manager. It also manages the X servers and facilitates remote logins using the XDMCP protocol.<br/>Network Manager - NetworkManager is a set of co-operative tools that make networking simple and straightforward. Whether WiFi, wired, 3G, or Bluetooth, NetworkManager allows you to quickly move from one network to another user/sbin/modemmanager.<br/>Upstart Socket Bridge - The upstart-socket-bridge queries the Upstart init(8) daemon for all job configurations which start on or stop on the socket event. It then waits for an incoming connection on each specified socket(7) and when detected emits the socket event (socket-event (7)), setting a number of environment variables for the job to query.<br/>acpid - The acpid process is designed to notify user-space programs of ACPI events.<br/>These are just some examples of acceptable answers. There are others as well.
			# Make sure you are not logged into xsession, then restart lightdm with sudo service lightdm restart
			# It will automatically respawn itself. There is a line in the tty script that instructs the process to automatically restart in the case of failure or termination of the process.
			# The kernel starts the upstart daemon at system boot.
			# To reboot use either telinit 6 or shutdown -r. To shutdown use either telinit 0 or shutdown tool with -h option and a time.
			# The links point to /lib/init/upstart-job. Ubuntu is transitioning from SysVinit scripts to upstart scripts, these links are used to redirect to the upstart services.
			# sudo apt-get install openssh-server.
			# The init.d script is used only for chroot environments. See lines 14-26 in init.d/ssh script.
			# Can check syslog process to see which logs it directly writes too. Some acceptable answers are:
			## auth.log - CRON, lightdm, polkitd
			## boot.log - modem-manager
			## bootstrap.log - gpgv, dpkg
			## dpkg.log - dpkg
			## fontconfig.log - fontconfig
			## kern.log - kernel
			## pm-powersave.log - powerd
			## pm-suspend.log - sleepd
			## ufw.log - ufw
			# test -x /usr/sbin/sshd \|\| exit 0 - Check whether "/usr/sbin/sshd" exists and is executable and exit with status of 0 if not. Used to verify SSHD is installed.<br/>( /usr/sbin/sshd -\? 2>&1 \| grep -q OpenSSH ) 2>/dev/null \|\| exit 0 - Runs SSH script with illegal option and pipes the output to grep to check for OpenSSH. Rest is piped to /dev/null essentially discarding it. This line checks to verify that the version of SSH installed is OpenSSH. If not will exit with status of 0.
			# test -x /usr/sbin/sshd \|\| { stop; exit 0; }<br/>Does not have a check for OpenSSH.
			# Plymouth is a bootsplash. It provides a graphical boot animation while the boot process takes place in the background.
			# not given.

Sdp: added answers for lab 1

2012-10-22T22:06:02Z

added answers for lab 1

@@ Line 1: / Line 1: @@
 Questions from Lab 1
 # What Linux distribution are you using?  What version?  You should look at the file <tt>/etc/issue</tt> generally to find out.
 # What shell do you get by default when you log in?  Check by running <tt>echo $SHELL</tt>.  If it is not ''bash'', then type <tt>exec bash</tt> to switch to it.
@@ Line 121: / Line 122: @@
 # Create a C program "mycopy-blocks.c" that takes three arguments: a block size and two filenames A and B as command line arguments.  This program should copy the contents of A to B, making B a byte-for-byte copy of A, except that the length of B should be evenly divisible by the block size.  The file should be padded with nulls as necessary.  Zero bytes in A should consume little to no space in B, however, including the padding.
 # How could loopback mounts be useful when working with virtual machines?  What conditions must the VM software meet for this to work?

Sdp: added questions from lab 4

2012-10-22T21:54:57Z

added questions from lab 4

← Older revision		Revision as of 21:54, 22 October 2012
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	}		}
	</code>		</code>

			Questions from Lab 4

			# Run the command <tt>truncate -s 1G foo</tt>. What is the logical size of foo, and how much space does it consume on disk?
			# Run <tt>mkfs.ext4 foo</tt>. (Say "yes" to operating on a regular file.) What is the logical size of foo now, and how much space does it now consume on disk?
			# What command do you run to check the filesystem in foo for errors?
			# Run <tt>mount foo /mnt</tt>. What does this command do?
			# Run <tt>df</tt>. What device is mounted on /mnt? What is this device?
			# Run <tt>rsync -a -v /etc /mnt</tt>. What does this command do? Explain the arguments as well.
			# Run <tt>umount /mnt</tt>. What files can you still access, and what have gone away?
			# Run <tt>dd if=/dev/zero of=foo conv=notrunc count=10 bs=512</tt>. What does this command do?
			# Run <tt>mount foo /mnt</tt>. What error do you get?
			# What command can you run to make foo mountable again? What characteristic of the file system enables this command to work?
			# Create a simple C program to generate a file consisting of the word "Hello", one thousand bytes of blank space (null bytes), and then "world\n", and then another thousand null bytes, such that the file produced consumes the maximum amount of space given its contents.
			# Create a C program "mycopy-blocks.c" that takes three arguments: a block size and two filenames A and B as command line arguments. This program should copy the contents of A to B, making B a byte-for-byte copy of A, except that the length of B should be evenly divisible by the block size. The file should be padded with nulls as necessary. Zero bytes in A should consume little to no space in B, however, including the padding.
			# How could loopback mounts be useful when working with virtual machines? What conditions must the VM software meet for this to work?

Sdp: fixed formatting on Lab 3 questions

2012-10-22T21:54:05Z

fixed formatting on Lab 3 questions

← Older revision		Revision as of 21:54, 22 October 2012
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	# Is the line "Is this line printed?" printed when you execute '''./run-program /bin/ls -a /tmp'''? Why?		# Is the line "Is this line printed?" printed when you execute '''./run-program /bin/ls -a /tmp'''? Why?
	# Change the program to use execve instead of execvp. What is the difference between the two functions?		# Change the program to use execve instead of execvp. What is the difference between the two functions?
			</ol>
	# Linux signals is a simple form of IPC that is used for a variety of purposes.		# Linux signals is a simple form of IPC that is used for a variety of purposes.
	<ol style="list-style-type: lower-alpha;">		<ol style="list-style-type: lower-alpha;">
	# What signal is generated when a program attempts to divide by zero? Give a simple program that generates such a signal.		# What signal is generated when a program attempts to divide by zero? Give a simple program that generates such a signal.
	# How would you send a signal to a process to have it pause execution? Resume?		# How would you send a signal to a process to have it pause execution? Resume?
			</ol>
	# What command can lower the priority of an already running process?		# What command can lower the priority of an already running process?
	# Why do we "open" files? Specifically, to what extent is it possible to do file I/O without open and close operations - assuming you could change the UNIX API?		# Why do we "open" files? Specifically, to what extent is it possible to do file I/O without open and close operations - assuming you could change the UNIX API?