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A process executes the following code

for(i=0; i<n; i++) fork();

The total number of child processes created is

  1. $n$
  2. $2^n-1$
  3. $2^n$
  4. $2^{n+1} - 1$
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Each fork() creates a child which start executing from that point onward. So, number of child processes created will be $2^n - 1$.

At each fork, the number of processes doubles like from $1 - 2- 4 - 8 ... 2^n$. Of these except $1$, all are child processes.

Reference: https://gateoverflow.in/3707/gate2004-it_64

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At each fork, the number of processes doubles like from 1 - 2- 4 - 8 ... 2n. Of these except 1, all are child processes. 

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         F0       // There will be 1 child process created by first fork

      /     \

    F1      F1    // There will be 2 child processes created by second fork

   /  \    /  \

 F2   F2  F2   F2  // There will be 4 child processes created by third fork

/ \   / \ / \  / \

 ...............   // and so on

If we sum all levels of above tree for i = 0 to n-1, we get 2n - 1. So there will be 2n – 1 child processes. On the other hand, the total number of process created are (number of child processes)+1.

 

Note:The maximum number of process is 2n and may vary due to fork failures.Also see this post for more details.

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