Write short notes:
        i) System Programming   ii) Unix Kernel API   iii) Shell Scripting   iv) File Attributes

A file whose file descriptor is fd contains the following sequence of bytes: 3, 1, 4, 1, 5, 9, 2, 6, 5, 3, 5. The following system calls are made:

Iseek(fd, 3, SEEK_SET);
read(fd, &buffer, 4);

where the Iseek call makes a seek to byte 3 of the file. What does buffer contain after the read has completed?

Depict the control flow of system calls. Do you agree/disagree that the system calls are time consuming? Give your statement. How do you change file permissions in Unix Explain with example.

cd [<dir>] means that change pwd to HOME directory, or <dir> if it is supplied. However, "Changing directories" and "being in a directory" are imprecise phrases. When you cd to a directory named dir, you may think of yourself as being "in dir", but this is not true. What is the true meaning for cd [<dir>] in order to resolve the relative pathnames?

In multi-user operating system, the operating system must protect users from each other and protect itself from users. However, while providing an operating environment for all users, the operating system creates this illusion (permission for read, write, execution, etc.) by creating data paths between user processes and devices and files. How does UNIX create this illusion?

Each user has a username and a number, the UID, why? Wouldn't it be simpler to record the username of the user as the owner of a file? Why not have a single identifier for each user?

A system call is like a conventional function call in that it causes a jump to a subroutine followed by a return to the caller. But it is significantly different. Distinguish between system call and function call based on the following keywords: privileged/kernel mode, trap instruction, system dependent.

Unix files have a full set of permission bits, including a set-user-ID bit and a set-group-ID bit. If you turn on the set-group-ID bit for a directory, does it have any effect? If so, what and why? If not, could you think of some use for this bit?

Analyze the following three commands:

i) ps-ax | grep cron

ii) ps-ax | tee processes.txt | more

The kernel had to locate a free inode and free disk blocks when it created a new file. How does the kernel know which blocks are free? How does the kernel know which inodes are free? What method does the file system on your machine use to keep track of unused blocks and inodes?

A directory is just a node in a set of linked nodes. Using the pwd command you can simply know the current directory. Based on the functionalities of pwd answer the following:

i) What repetitive steps are performed to compute its current directory?
ii) How do we know when we read the top of the tree?
iii) How do we print the directory names in the correct order?

The hypothetical machine of Fig. 1 also has two I/O instructions:

Assume that the next value retrieved from device 5 is 3 and location 940 contains a value of 2.

In UNIX, there is a single file hierarchy and every accessible file is in this single file hierarchy, no matter how many disks are attached. Similar to windows, there is no such thing as the "C" drive" or "E" drive" in UNIX. If any new file system arrive then how UNIX adapt itself? Give example(s).

How does ls -1 work? Briefly explain the data flow in who command with figures.

How can we design a multithreaded program to count and print the total number of words in three files? Give two use case scenarios for clarification.

Write short notes on the following:

i) pthread_create, pthread_join
ii) pthread_mutex_lock, pthread_mutex_unlock