README.md

System Calls

• fork()
• wait()

PROCESS SYSTEM CALL

• getpid() and getppid()

  • The getpid system call returns process ID of the calling process
  • The getppid system call returns parent process ID of the calling process

• fork()

  • The fork system call is used to create a new process called child process.
    • The return value is 0 for a child process.
    • The return value is negative if process creation is unsuccessful.
    • For the parent process, return value is positive
  • The child process is an exact copy of the parent process.
  • Both the child and parent continue to execute the instructions following fork call.
  • The child can start execution before the parent or vice-versa.

• wait()

  • The wait system call causes the parent process to be blocked until a child terminates.
  • When a process terminates, the kernel notifies the parent by sending the SIGCHLD signal to the parent.
  • Without wait, the parent may finish first leaving a zombie child, to be adopted by init process

• exit()

  • The exit system call is used to terminate a process either normally or abnormally
  • Closes all standard I/O streams.

• execl()

  • The exec family of function (execl, execv, execle, execve, execlp, execvp) is used by the child process to load a program and execute.
  • execl system call requires path, program name and null pointer

• stat()

  • The stat system call is used to return information about a file as a structure.

• opendir(), readdir() and closedir()

  • The opendir system call is used to open a directory
    • It returns a pointer to the first entry
    • It returns NULL on error.
      • The readdir system call is used to read a directory as a dirent structure
    • It returns a pointer pointing to the next entry in directory stream
    • It returns NULL if an error or end-of-file occurs.
  • The closedir system call is used to close the directory stream
    • Write to a directory is done only by the kernel.