(Written) Assignment 1 - 10 Marks

1. Understand the Mars Pathfinder Problem and how it was solved and write it down in your own words. (3 Marks)

2. Take the output of the ps command and identify which are the processes being run by you. Trace the tree to the root for two of these processes. Verify that the root of the tree is the init process. Explain what commands or process you used to trace the tree. (2 Marks)

3. Many CPU scheduling algorithms are parameterized. For example, the RR algorithm requires a parameter to indicate the time slice. Multilevel feedback queues require parameters to define the number of queues, the scheduling algorithms for each queue, the criteria to move processes between queues and so on.

These algorithms are thus really sets of algorithms (for e.g., the set of RR algorithms for all time slices and so on). One set of algorithms may include another (for e.g., the FCFS algorithm is the RR algorithm with an infinite time quantum). What (if any) relation holds between the following pairs of sets of algorithms? (2 Marks)

• Priority and SJF
• Multilevel Feedback Queues and FCFS
• Priority and FCFS
• RR and SJF

4. Write short notes on the differences between Linux 2.6 and Linux 2.4 schedulers. (3 Marks)

Read Understanding the /proc file system. Understand the entries and the contents of various files in this directory /proc.

Write a program to read the /proc filesystem and print the following for all the processes listed there:

PID, PPID, STATE, COMMAND, No. of Files open

Since for all the root or privileged processes, you are not allowed to read the no. of files open, print NA for those. For all user processes, print the no. of files open.

Below are some Hints for the assignment.

• Use the systems calls - opendir, chdir, readdir for opening, changing to and reading the contents of a directory. If you do not change to the directory you are opening, make sure the path is correctly set by concatenating the path to the file/directory you are trying to open.
• Remember to check the return value of every system call you are using. This is most important for system calls. In fact, without this, you will find yourselves in a lot of trouble to debug or understand what is happening.
• Typically, system calls only return -1 when there is an error. They set a global error number variable called errno which is defined in errno.h. Since it is difficult to understand the number itself, Unix/Linux provides the function strerror(errno) to print a human-readable string which gives the error encountered. Use this to debug your code.
• Use fopen and fgets calls to read the contents of a directory. Then use either strchr, strtok or sscanf to parse the contents of the file and read the pid, ppid etc. values.
• Make sure your code is modular with different functions doing different logical pieces of work and unit test these functions as you build them to enable fewer bugs. If you write the complete program and only then try to debug, you may find yourself bogged down.