passwd command in linux is used to change the user password
to set or print the system time and date. date [OPTION]… [+FORMAT]. $date. Output: Tue Aug 27 09:54:25 DST 2019. Explanation : the date command prints the current date and time of the system in a fixed format string as above. The format string is Abbreviated_week_day abbreviated_month day_of_the_month time(hh:mm:ss) time_zone YYYY(year).
Zombie process is a process which has terminated but its entry still exists in the process table until the parent terminates normally or calls wait()
If you are a programmer, you create a program by writing a code and when you run that program it becomes a process. It is very important to have a clear difference between a program and a process because one program can produce many running processes that are just different versions of a single program.
execl() or execlp() functions are used to replace the image of the current process with a new process image. In other words the current process code gets replaced by the new process code.