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.

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.

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.

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

What is the difference between system calls and library functions in system programming?

Can you list the chapter topics that are scheduled to be covered in today's syllabus?

Depict the top of a typical UNIX directory hierarchy. How does 1s.-1 work? Explain.

In Linux, what does the file permission rwxr-xr-- represent?

What is the significance of learning both Operating Systems and System Programming in the same curriculum?
 

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?

What system call is used for reading a file in C, and how is it different from fread()?

Create a scenario that showcases your comprehensive understanding of the topics covered in this course.
 

What does the stat() system call do, and how is it used to retrieve file properties?

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.

Fig-1

How can you view the recent user login records on a Linux system?

Note regarding the preparation you have taken before attending the Mid Term Exam.

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

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.

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?

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.

The stat system call is passed the name of a file and a pointer to a struct and fills the struct with information about the file. Explain, using the directory, inode, and data model, how stat works?

Explain in detail how the chmod 754 command changes file permissions. Break down the numeric mode and describe what each number (7, 5, and 4) means in binary, and which permissions they correspond to for the file owner, group, and others.

A Linux system administrator is investigating a multi-user server to track who is currently logged in and how to monitor system access. The who command is used to list currently logged-in users by reading the /var/run/utmp file, which stores login session information.

To build a custom tool that mimics the who command, a developer decides to read /var/run/utmp directly using low-level Unix system calls: open(), read(), and close(). Here's how the system calls might be used:

Describe how the who command works internally on Unix-based systems, and explain the role of the low-level system calls open(), read(), and close() in this process.

Your answer should include:

• What file the who command reads (/var/run/utmp) and what kind of information it contains.
• The use of struct utmp to interpret the binary data stored in the file.
• A comparison between low-level system calls (open(), read(), close()).

A system administrator creates a new user account named alice on a Unix-based system. This user creates several files in her home directory:

touch /home/alice/report.txt

Later, alice is deleted from the system. However, her files remain. The output of Is -1 /home/alice/ still shows alice as the file owner.

Some days later, a new employee joins, and the administrator creates a new user also named alice, assigning her a new home directory.

Despite having the same username, this new alice is technically a different user from the system's point of view.

Now, answer the following questions:

i) Describe how the Is command retrieves and displays file ownership and permissions.

ii) Explain what happens when a user is deleted and later a new user is created with the same username.

iii) Given the situation where the original alice had UID 1001 and the new alice is assigned UID 1002, describe what will happen to the files created by the old user.

When a new file is created on a Unix-based system, the kernel must allocate both an inode and one or more data blocks. Explain how the file system determines which inodes and disk blocks are available for allocation. In your explanation, discuss the data structures or mechanisms used to track free inodes and blocks (such as bitmaps or free lists), and describe how modern file systems (e.g., ext4) manage this process efficiently.

Describe how thread creation and management is handled in POSIX-compliant systems using the pthread library.

To a programmer, a system call looks like any other call to a library procedure. Is it important that a programmer know which library procedures result in system calls? Under what circumstances and why?

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?

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?

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?

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?

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 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.

Assuming the default umask is 022, what would the original permissions of backup.sh be right after it was created? Explain how umask affects file creation permissions and why Asif might have needed to change them

What are the potential problems of using multiple threads in a shared-memory environment, and how can these problems be mitigated?

A very significant issue for system programming is the handle of I/O devices for accessing the abstraction. Differentiate the access criteria of I/O devices for UNIX and C.

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.

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?

Analyze the following three commands:

i) ps-ax | grep cron

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

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

Write short notes on the following:

i) pthread_create, pthread_join
ii) pthread_mutex_lock, pthread_mutex_unlock

If Asif wants to allow only themselves to read, write, and execute the file while preventing everyone else (group and others) from even reading it, what chmod command should be used? Describe the reasoning and verify the new permission set with symbolic representation (rwxr--r--, etc.).

Explain the difference between a process and a thread in the context of system programming.

 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.