JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III Year LINUX PROGRAMMING Previous Question Paper (October - 2020 - R13)

Linux provides a suite of utilities for managing processes and disk resources. Below are the primary commands for each category.

Process Utilities

1. ps: Displays information about active processes. Example: ps aux shows all running processes for all users.
2. top: Provides a dynamic, real-time view of the system's running processes and resource usage.
3. kill: Sends a signal to a process to terminate it. Example: kill -9 1234 forces the process with PID 1234 to terminate.
4. nice/renice: Adjusts the scheduling priority of a process. Example: nice -n 10 ./script.sh runs a script with a lower priority.
5. pgrep/pkill: Searches for or terminates processes based on name or other attributes. Example: pgrep firefox returns the PID of the Firefox process.

Disk Utilities

1. df: Reports file system disk space usage. Example: df -h displays disk usage in a human-readable format (GB/MB).
2. du: Estimates file space usage for directories and files. Example: du -sh /home/user summarizes the total size of the user directory.
3. fdisk: A menu-driven command-line utility for disk partition manipulation. Example: fdisk -l lists all available partitions on the system.
4. mount/umount: Attaches or detaches a file system to the directory tree. Example: mount /dev/sdb1 /mnt/data mounts a partition to a specific directory.
5. fsck: Used to check and optionally repair file system inconsistencies. Example: fsck /dev/sda1 checks the integrity of the specified partition.

In the Unix file system, every file and directory is associated with an owner and a group, and access is controlled through permissions defined for three categories: the owner (u), the group (g), and others (o). Permissions are categorized into read (r), write (w), and execute (x).

File Ownership Commands:

• chown: Used to change the owner of a file or directory. The syntax is
  chown [owner] [file]
  . Only the superuser can change the owner of a file.
• chgrp: Used to change the group ownership of a file or directory. The syntax is
  chgrp [group] [file]
  .

File Permission Commands:

• chmod: Used to change the access permissions of a file. It supports two modes:
  • Symbolic Mode: Uses operators like + (add), - (remove), and = (set). For example,
    chmod u+x filename
    adds execute permission for the owner.
  • Absolute (Octal) Mode: Uses three-digit numbers where 4 represents read, 2 represents write, and 1 represents execute. For example,
    chmod 755 filename
    sets read, write, and execute for the owner (4+2+1=7), and read and execute for the group and others (4+0+1=5).
• umask: Sets the default permissions for newly created files. It acts as a bitwise mask subtracted from the default system permissions (usually 666 for files and 777 for directories).

The ls -l command is used to view these attributes, displaying a string like