Process management

Minimal shell:

1. Wait for command
2. Start process to execute command
3. Wait until process finished

pid_t fork()

• duplicates current process
• negative value — unsuccessful
• zero — returned to newly created child process
• positive — returned to parent or caller, value is PID of new process

pid_t wait(int *wstatus)

• waits for child processes to change state
• writes status to wstatus

int exec(const char *path, char *constargv[])

• loads new binary from path in current process
• constargv — program arguments
• last argument is NULL (e.g. constargv = {“/bin/ls”, “-a”, NULL})

signals

• processes may need to be interrupted
• a signal is sent to process that needs to be interrupted
• interrupted process catches signal using signal handler
• sighandler_t signal(int signum, sighandler_t handler)
  • registers signal handler
• unsignedint alarm(unsigned int secs)
  • deliver SIGALARM in seconds
• int kill(pd_t pid, int sig)
  • deliver signal to pid

pipes

• pipe(fd) sets up a pipe
• fd is array of 2 ints