Activities

These are the activities of the unit. Do them in order, after you read the matching notes. Activities 1, 3 and 4 use the Process & CPU Scheduler Lab.

Hand in every activity in Aules, in the matching task, as a document (PDF, ODT or DOCX) with your name. You do not need to copy the questions: number your answers. Write in English if you can. Do not include personal data (passwords, private photos) in your screenshots.

For activities 1, 6 and 7 you need an Ubuntu virtual machine (the one from Unit 2 is fine). Never practise partitioning or formatting on your real disk.

Activity 1 · Processes in Linux

Objective: observe the processes of a Linux system, change their state and read their information.

What you have to do:

1. Open the tab Terminal of the lab and complete the six missions of the list. Then repeat the main steps in your Ubuntu virtual machine.
2. In a terminal run ps aux | head -15. Write the PID, USER and STAT of five processes. Run echo $$ to find the PID of your shell and find it in the list.
3. Run sleep 300 &. With jobs and ps -o pid,ppid,stat,cmd -p <PID> write its PID, its parent and its state. Stop it with kill -STOP <PID>, check the state again, continue it with kill -CONT <PID> and end it with kill <PID>. Copy each command and the STAT letter that you saw.
4. Run yes > /dev/null &. Open top (or htop) and find it: what %CPU does it use? Change its priority with renice -n 19 -p <PID> and describe what changes. End it with kill.
5. Create a zombie with the command of the notes (bash -c 'sleep 2 & exec sleep 300' &). Show with ps that there is a process in state Z. Try kill -9 on the zombie and explain what happens. Then remove it and explain how.
6. Run systemctl status cron (or another service of your system). Say if it is active, since when, and what its PID is. Is it a user process or a system process? Is it a service?
7. Fill in a table of at least six processes with columns: PID, PPID, user, state, type (user, system or service) and what it does.

What you hand in: a document with the commands, the relevant output (text or screenshots) and your explanations. Task “Activity 1” in Aules.

Criteria that it works on: RA1.c, RA2.a, RA4.c

Difficulty: ★★☆ · Estimated time: 75 minutes

Activity 2 · Processes and services in Windows

Objective: do in Windows the same observations as in Linux and compare both systems.

What you have to do:

1. Open Task Manager (Ctrl + Shift + Esc). In the Details tab, add the columns PID, Status, User name and Priority (right click on a column header → Select columns).
2. Open Notepad and find notepad.exe: write its PID, user and memory. Close it with End task and check that it disappears.
3. Find three processes that run with the user name SYSTEM, LOCAL SERVICE or NETWORK SERVICE and three that run with your user name. Write what each of them does (look it up in the official documentation if you need to).
4. Open PowerShell and run while ($true) {}. This uses one CPU core. Find the powershell.exe process that uses most CPU, change its priority to Below normal and describe what you see. Close the window to stop it.
5. Open services.msc. For three services (for example Print Spooler, Windows Time and Windows Update) write the status, the startup type and the account used to log on. Do not change anything.
6. Answer: what is the difference between Automatic, Manual and Disabled? Why does Windows have a svchost.exe process for several services?
7. Make a comparison table with five rows: how to list processes, how to end one, how to change its priority, how to list services and how to start or stop a service. One column for Linux and one for Windows.

What you hand in: the document with screenshots and the comparison table. Task “Activity 2” in Aules.

Criteria that it works on: RA1.c, RA2.a, RA4.c

Difficulty: ★☆☆ · Estimated time: 60 minutes

Activity 3 · Scheduling by hand

Objective: calculate scheduling results with a Gantt chart and check them with the simulator.

What you have to do:

1. Load A. Use FIFO, SJF and SRTF. Draw a Gantt chart for each one and calculate the completion, response and waiting time of every process and the averages.

   Process	Arrival	Burst
   P1	0	7
   P2	2	4
   P3	3	1
   P4	5	3

2. Load B. Use priorities (non-preemptive), priorities (preemptive) and Round Robin with q = 3. A lower number is a higher priority. Same work as in the first part.

   Process	Arrival	Burst	Priority
   P1	0	5	3
   P2	1	3	1
   P3	2	6	4
   P4	4	2	2

3. Enter both loads in the tab Scheduler simulator and compare its results with yours. If there is a difference, find your mistake and correct it.

4. Which algorithm gives the best average waiting time in each load? Which one is the least fair, that is, makes a process wait for longest? Explain in two or three sentences.

5. Do three exercises of the tab Practice and write the number of correct answers.

What you hand in: the six Gantt charts (a photo of your handwriting is accepted) with the tables and your answers to 4 and 5. Task “Activity 3” in Aules.

Criteria that it works on: RA1.c, RA2.a

Difficulty: ★★★ · Estimated time: 90 minutes

Activity 4 · Quantum and starvation

Objective: investigate with the lab how the quantum and the choice of algorithm change the results.

What you have to do:

1. In the tab Algorithm shoot-out, use the preset Five processes (or enter this load: P1 0/8/3, P2 1/4/2, P3 2/9/4, P4 3/5/1, P5 6/2/2, where each triple is arrival/burst/priority). Write a table with the average waiting time, the average response time and the context switches of the six algorithms, with Round Robin at q = 3.
2. Move the quantum slider from 1 to 8. Copy the results for q = 1, 2, 4 and 8 and draw a conclusion: what happens to the context switches? What happens to the response time? What does the algorithm look like when q is very big?
3. Choose a quantum that you think is a good compromise and justify it.
4. In the Starvation part, put 3, 6 and 8 short processes. Write the waiting time of the long process without aging and with aging. Explain the numbers.
5. A desktop computer has a window manager, a video player and a backup program. Which algorithm would you use and why? Mention at least one problem of your choice and how to reduce it.

What you hand in: the tables, the conclusions and your answers. Task “Activity 4” in Aules.

Criteria that it works on: RA2.a, RA4.c

Difficulty: ★★☆ · Estimated time: 60 minutes

Activity 5 · Memory: calculate, observe and optimise

Objective: do the memory calculations of the unit and check the memory of a real computer.

What you have to do:

1. Fragmentation. A system has fixed partitions of 128 KiB. Processes of 100, 30, 128 and 65 KiB are loaded. How much memory is wasted in each partition? What kind of fragmentation is it?
2. Paging. The page size is 1 KiB (1024 bytes). The page table of a process is: page 0 → frame 4, 1 → 9, 2 → 1, 3 → 7, 4 → 3, 5 → 0. Calculate page, offset and physical address for the logical addresses 2600, 5300, 1030 and 7000. One of them causes a problem: which one and why?
3. Segmentation. A process has these segments (base, limit): S0 (3000, 2200), S1 (8000, 600), S2 (12000, 1500). Translate (0, 1500), (1, 600), (2, 1499) and (1, 599), or say that the access is not valid.
4. Page replacement. With the reference string 7 1 4 1 7 3 4 3 1 7 5 7 4 1, count the page faults with FIFO and LRU, first with 3 frames and then with 4 frames. Show the frames after every reference. What do you observe when you compare LRU with FIFO in the case of 3 frames?
5. Observe. On your own computer (or in a virtual machine), find: total RAM, available RAM and swap (or page file) in use. In Linux use free -h and swapon --show; in Windows, Task Manager → Performance → Memory. Find the three processes that use most memory.
6. Optimise. Propose three realistic actions to reduce the memory use of that computer. For each one say what you would measure before and after. If you can, try one and report the difference.

What you hand in: the calculations (show the steps), the table of data and the three proposals. Task “Activity 5” in Aules.

Criteria that it works on: RA2.a, RA4.e

Difficulty: ★★★ · Estimated time: 100 minutes

Activity 6 · Partitions, file systems and an installation plan

Objective: partition a virtual disk, compare three file systems and write an installation plan.

What you have to do:

1. In VirtualBox, add a new virtual disk of 2 GiB to your Ubuntu virtual machine (the machine must be switched off). Start it and open GParted (install it with sudo apt install gparted if needed).
2. Select the new disk (check its name with lsblk!). Create a partition table of type msdos (MBR). Create three primary partitions: 300 MiB FAT32 (label FAT), 700 MiB NTFS (label NTFS) and 600 MiB ext4 (label EXT). Apply the changes.
3. Answer the following questions with GParted or the terminal: Can you create a fourth primary partition in the free space? And a fifth one? How? Can you make the NTFS partition bigger? What happens to the data if you shrink a partition?
4. Mount the three partitions (click on them in the file manager). In each one create files named Data.txt and data.txt, then run chmod 600 Data.txt and ls -l. Fill in a table: does the file system distinguish capital letters? Does it keep the permissions? Show the output.
5. Run df -h and lsblk -f and add the output to your report. Say the size of each file system and how much of it is already used.
6. Delete the three partitions, convert the disk to GPT (Device → Create Partition Table → gpt) and create five primary partitions. What changes? Write a table with five differences between MBR and GPT.
7. Write a table that compares FAT32, NTFS and ext4: maximum file size, permissions, journaling, case-sensitivity and typical use. Mark which ones you proved yourself in step 4.
8. Installation plan. A school wants Ubuntu Desktop on a computer with 8 GiB of RAM, an 80 GiB SSD and UEFI. Write a plan with the points of the table in section 7 of page 4: hardware check, partition table, partitions with size, file system and mount point, users, backup and checks.
9. Say in one paragraph when you would choose a journaling file system and what would happen after a power cut in each of the three file systems.

What you hand in: screenshots of GParted before and after, the outputs, the tables and the plan. Task “Activity 6” in Aules.

Criteria that it works on: RA1.d, RA1.e, RA1.g, RA2.e, RA4.g

Difficulty: ★★★ · Estimated time: 120 minutes

Activity 7 · Permissions and shared resources

Objective: read and change permissions in Linux and Windows and configure a simple share.

What you have to do:

1. In your Linux virtual machine create a folder project with a file notes.txt and a script run.sh (with the text echo hello). Run ls -l and explain every field of the three lines (type, permissions, owner, group).
2. Write the chmod commands (in octal) to obtain each case and test them: (a) notes.txt readable and writable by the owner, readable by the group and no access for others; (b) run.sh executable by everybody and writable only by the owner; (c) the folder project accessible only by its owner. Try to run ./run.sh before and after you add the x permission.
3. Create a second user (sudo adduser guest1). Test with sudo -u guest1 cat project/notes.txt in cases (a) and (c). Explain the results with the permissions of the file and of the directory.
4. Explain what happens when a directory has r-- but not x, and when it has --x but not r.
5. In Windows (or a Windows virtual machine) create a folder Shared on an NTFS disk with a file inside. In the Security tab give the group Users only Read. Then add a Deny for Write to a test user. What is the effective permission of that user? Why?
6. Share the folder: Properties → Sharing → Advanced Sharing, with a share permission of Read for one user. From another computer (or the same one) open \\COMPUTERNAME\Shared. Try to create a file. Which permissions are being applied, the share one or the NTFS one? Which wins?
7. Write five good practices for sharing resources in a network and one risk that each one avoids.
8. Look at the permissions of /etc/passwd, /etc/shadow and /tmp (ls -ld). Why do you think they are different?

What you hand in: a document with the commands, outputs and screenshots and your answers. Task “Activity 7” in Aules.

Criteria that it works on: RA1.e, RA1.f, RA4.h

Difficulty: ★★☆ · Estimated time: 90 minutes

🔒 Material en Aules

You hand in all the activities in Aules, in the task of each one. There you will also find the assessment criteria, your marks and the solutions.

Abrir el curso en Aules