Why can't we change directories through system() system call in Linux?

Question

system (\"cd ..\");

This doesn\'t produce any error but also doesn\'t do anything meaningful. Why?

Answer 1

That's because it executes another shell. Inside this shell, the working directory changes, but that has no effect on the calling program.

Answer 2

system runs the command you passed it in a different process (in a subshell). That subshell changes directories and promptly exits.

That's all perfectly valid, but perfectly useless. Use chdir to change your working directory.

Answer 3

The system() function makes a fork() that creates a process being a copy of the initial one.

The current directory depends on the environment of a process (it is stored within the environment variables of a process). Thus when the child process, having its own environment, makes a cd, that affects only the child process, not the parent.

• Parent process: in /home/x/y

• Child process (after the fork): in /home/x/y

Doing a cd .. in the child process sets its local environment to /home/x
But the parent process is still in /home/x/y

Parent process waits for child to complete the system call, then continue its own execution having its own environment (current directory) unchanged.