What is a shell?
A shell is an interactive user interface to an operating system services
that allows an user to enter commands as character strings or through a
graphical user interface. The shell converts them to system calls to the
OS or forks off a process to execute the command. System call results and
other information from the OS are presented to the user through an interactive
interface. Commonly used shells are sh,csh,ks etc.
Brief about the initial process sequence while the system boots up.
While booting, special process called the 'swapper' or 'scheduler' is
created with Process-ID 0. The swapper manages memory allocation for processes
and influences CPU allocation. The swapper inturn creates 3 children:
What are various IDs associated with a process?
Unix identifies each process with a unique integer called ProcessID.
The process that executes the request for creation of a process is called
the 'parent process' whose PID is 'Parent Process ID'. Every process is
associated with a particular user called the 'owner' who has privileges
over the process. The identification for the user is 'UserID'. Owner is
the user who executes the process. Process also has 'Effective User ID'
which determines the access privileges for accessing resources like files.
Explain fork() system call.
The `fork()' used to create a new process from an existing process.
The new process is called the child process, and the existing process is
called the parent. We can tell which is which by checking the return value
from `fork()'. The parent gets the child's pid returned to him, but the
child gets 0 returned to him.
Predict the output of the following program code
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