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Cork Institute of Technology
Higher Certificate in Science in Computing in Information Technology
Support - Award
(KITSU_6_Y2)
Autumn 2008
Operating Systems
(Time: 2 Hours)
Instructions Answer FOUR questions. All questions are worth equal marks.
Examiners: Mr. G. McSweeneyMr. J. Greenslade Mr. J. Walsh
Q1 (a). Write down six advantages of UNIX / Linux. ( 6 Marks )
(b) Write down three disadvantages of UNIX / Linux. ( 3 Marks ) (c) Name two Linux distributions. ( 2 Marks ) (d) KDE is a Linux GUI , name another. ( 1 Mark ) (e) Name the Marks ) three categories of potential users of a file. ( 3
(f) What (^) type of files would you expect to have in the following directories?
/ bin /etc /dev /root /home ( 5 Marks ) (g) Describe how a system authenticates a user’s password. ( 2 Marks ) (h) Why can a user be satisfied his / her password is relatively secure? ( 2 Marks ) (i) What is the primary purpose of a shell? ( 1 Mark )
Q2. (a) Write a shell script which copies the entire contents of a user’s home drive (including subdirectories) to a remote media mounted atremove any unwanted files from the user’s home drive. /media/remote. The script should also ( 6 Marks ) (b) How might the same script be adapted to enableothers’ backups? all users to use it without wiping each( 2 Marks ) (c) How might the confidentiality of all backups be guaranteed on the backup media?( 2 Marks )
(d) What is the purpose of the grep command? ( 2 Marks ) (e) What is the purpose of the environmental variable PATH? ( 2 Marks ) (f) How might a user make a permanent change to his / her PATH? ( 2 Marks ) (g) Write down two other environmental variables. ( 2 Marks ) (h) Name the two different types of links. ( 2 Marks ) (i) What type of link would be appropriate to link a file on a USB key to a file on the hard disk?( 1 Mark )
(j) Explain your answer to ( i ). ( 2 Marks ) (k) Users often haveand why are they hidden. (^) hidden files in their home directories. What is the purpose of hidden files( 2 Marks )
Q4. (a) Apart from encrypting passwords, suggest another use for one-way encryption algorithms. ( 2 Marks ) (b) Write down an example of a common one-way encryption algorithm. ( 2 Marks ) (c) What is the purpose of the telnet protocol? ( 2 Marks ) (d) In recent years the telnet protocol has largely been replaced by another protocol – what is it?( 3 Marks )
(e) What type of encryption algorithm does the protocol in ( d ) deploy? ( 2 Marks ) (f) A user jane wants to sent a secret document to another user kate over an open network. Whattype of encryption be appropriate for this task? Describe how the document should be sent and how it would be protected from any interception. ( 8 Marks ) (g) Write down two examples of when a single key encryption might be useful. ( 2 Marks ) (h) What permissions should an administrator set to a directory to enable a group of users to onlycopy files from it? ( 2 Marks )
(i) What permissions should an administrator set to a directory to enable a group of users to onlywrite files to it? ( 2 Marks )
Q.
(a) What is the difference between a pre-emptive and a non pre-emptive scheduling algorithm?( 2 Marks )
(b) Write down an example of one pre-emptive algorithm and one non pre-emptive schedulingalgorithm. (2 Marks )
(c) Why might a process be blocked? ( 2 Marks )
Consider the following set of processes with duration given in milliseconds. Process Name Arrival Time Service Time P1 0 4 P2 1 2 P3 3 1 P4 4 3
(d) Draw a time line to show the execution of each of these processes for the time scheduling algorithm. For each algorithm, calculate the Turnaround Time and the shortest remaining Normalised Turnaround Time. ( 8 Marks ) (e) Explain why the actual service (and waiting) time is longer than indicated by the time line.( 2 Marks )
(f) Apart from normal completion, suggest five reasons why a process might be terminated.( 5 Marks )
(g) The command ps –af lists running process under the headings:
UID PID PPID C STIME TTY TIME CMD Explain the meanings of UID , PID , PPID and TTY. ( 4 Marks )
