15 Questions
What is the purpose of the execl function in C?
To execute an executable program with a specified path and list of command line arguments.
How does the execv function differ from execl?
The execv function takes a path name and a pointer to a list of character pointers (like argv[]) as command line arguments.
What does the fork() function do in C?
The fork() function creates a new process by duplicating the existing process.
How many distinct outputs are possible from the code segment: int main() { fork(); printf("a"); fork(); printf("b"); return 0; }?
4 distinct outputs are possible.
What is the purpose of the args array in the execv function call?
The args array holds the list of command line arguments passed to the new program.
What is the purpose of the execv function?
To execute an executable program by providing its path and list of command line arguments.
How is the list of arguments terminated in the execl function?
With a null pointer.
In the code segment int main() { fork(); printf("a"); fork(); printf("b"); return 0; }, how many distinct outputs are possible?
4 distinct outputs are possible.
What does the fork() function do in C?
The fork() function creates a new process by duplicating the existing process.
What is the purpose of the args array in the execv function call?
The args array holds the list of command line arguments for the new program.
How is the second argument passed to the execv function?
As a pointer to a list of character pointers.
What is the purpose of the argv parameter in the execv function?
The argv parameter holds the list of command line arguments for the new program.
How is the execv function different from the execl function?
execv takes the arguments as an array of strings, while execl takes them as separate string parameters.
What happens after the fork() function is called in a C program?
A new child process is created.
How does the execv function handle the execution of a new program?
execv replaces the current process image with the new program's image.
Study Notes
Exec System Call
- The exec system call is used when a new process is not part of the same program as the parent process, such as when a user starts a command in a shell.
- Exec replaces the contents of the currently running process with the information from a program binary.
Characteristics of Exec
- The exec function is a family of six functions, each with slightly different calling conventions and use.
- Exec is declared in the same location as fork.
- Exec completely replaces the calling process's image with that of the program being executed.
- Unlike fork, exec does not generate a new PID, as it replaces the original process.
- If successful, the exec calls do not return, as the calling image is lost.
Prototypes of Exec
- There are six prototypes of exec:
- execl
- execlp
- execv
- execvp
- execle
- execve
Naming Convention of Exec
- The naming convention for the "exec" system calls reflects their functionality:
- The function starts with "exec", indicating that it is part of the exec family.
- The next letter indicates if the call takes its arguments in a "list format" or as a pointer to an "array of arguments".
- The presence of a "p" indicates that the current PATH string should be used when searching for executable files.
- Functions whose name ends with an "e" allow passing an array to set a new environment.
Execl
- The execl function requires each command-line argument to the new program to be specified as separate arguments, terminated by a NULL pointer.
Explore the concept of exec system call in operating systems, which allows a new process to run independently from the parent process. Learn how exec replaces the current process image and loads a new program for execution.
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