What is relative path and absolute path.

What is relative path and absolute path.
Absolute path : Exact path from root directory.
Relative path : Relative to the current path.

Explain kill() in unix and its possible return values.

Explain kill() in unix and its possible return values.
There are four possible results from this call:
‘kill()’ returns 0. This implies that a process exists with the given PID, and the system would allow you to
send signals to it. It is system-dependent whether the process could be a zombie.
‘kill()’ returns -1, ‘errno == ESRCH’ either no process exists with the given PID, or security enhancements
are causing the system to deny its existence. (On some systems, the process could be a zombie.)
‘kill()’ returns -1, ‘errno == EPERM’ the system would not allow you to kill the specified process. This means
that either the process exists (again, it could be a zombie) or draconian security enhancements are present
(e.g. your process is not allowed to send signals to *anybody*).
‘kill()’ returns -1, with some other value of ‘errno’ you are in trouble! The most-used technique is to assume
that success or failure with ‘EPERM’ implies that the process exists, and any other error implies that it
doesn't.
An alternative exists, if you are writing specifically for a system (or all those systems) that provide a ‘/proc’
filesystem: checking for the existence of ‘/proc/PID’ may work.

What Happens when you execute a program in unix

What Happens when you execute a program in unix?

Question :What Happens when you execute a program in unix ?
Answer :When you execute a program on your UNIX system, the system creates a special environment for that program. This environment contains everything needed for the system to run the program as if no other program were running on the system. Each process has process context, which is everything that is unique about the state of the program you are currently running. Every time you execute a program the UNIX system does a fork, which performs a series of operations to create a process context and then execute your program in that context. The steps include the following: • Allocate a slot in the process table, a list of currently running programs kept by UNIX. • Assign a unique process identifier (PID) to the process. • iCopy the context of the parent, the process that requested the spawning of the new process. • Return the new PID to the parent process. This enables the parent process to examine or control the process directly. After the fork is complete, UNIX runs your program.
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What happens when you run a program?
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What is an advantage of executing a process in background

What is an advantage of executing a process in background

Question :What is an advantage of executing a process in background?
Answer :The most common reason to put a process in the background is to allow you to do something else interactively without waiting for the process to complete. At the end of the command you add the special background symbol, &. This symbol tells your shell to execute the given command in the background. Example: cp *.* ../backup& (cp is for copy)
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How do you execute one program from within another in unix

How do you execute one program from within another in unix

Question :How do you execute one program from within anotherin unix?
Answer :The system calls used for low-level process creation are execlp() and execvp(). The execlp call overlays the existing program with the new one , runs that and exits. The original program gets back control only when an error occurs. execlp(path,file_name,arguments..); //last argument must be NULL A variant of execlp called execvp is used when the number of arguments is not known in advance. execvp(path,argument_array); //argument array should be terminated by NULL
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