Unix Prog: Process Identifiers

1. System Calls:

There are a bunch of system calls used to to retrieve the:
process id
parent process id
process group id
real user id
effective user id
real group id
effective group id

System Definitions:

 ubuntu@ip-172-31-23-227:~$ less /usr/include/unistd.h  
 ......  
 /* Get the process ID of the calling process. */  
 extern __pid_t getpid (void) __THROW;  
   
 /* Get the process ID of the calling process's parent. */  
 extern __pid_t getppid (void) __THROW;  
   
 /* Get the process group ID of the calling process. */  
 extern __pid_t getpgrp (void) __THROW;  
 ......  
 /* Get the real user ID of the calling process. */  
 extern __uid_t getuid (void) __THROW;  
   
 /* Get the effective user ID of the calling process. */  
 extern __uid_t geteuid (void) __THROW;  
   
 /* Get the real group ID of the calling process. */  
 extern __gid_t getgid (void) __THROW;  
   
 /* Get the effective group ID of the calling process. */  
 extern __gid_t getegid (void) __THROW;  
 ......  

2. Example:
proc.c:

 #include<stdio.h>  
 #include<stdlib.h>  
 #include<unistd.h>  
   
 int main(int argc, char* argv[])  
 {  
  printf("%30s:%d \n", "Process ID", getpid());  
  printf("%30s:%d \n", "Parent Process ID", getppid());  
  printf("%30s:%d \n", "Process Group ID", getpgrp());  
  printf("%30s:%d \n", "real user id", getuid());  
  printf("%30s:%d \n", "effective user id", geteuid());  
  printf("%30s:%d \n", "real user group id", getgid());  
  printf("%30s:%d \n", "effective user group id", getegid());  
  exit(0);  
 }  

shell:
It indicates that current process id is 4048.

 ubuntu@ip-172-31-23-227:~$ ./proc.out  
           Process ID:4148  
        Parent Process ID:4069  
        Process Group ID:4148  
          real user id:1000  
        effective user id:1000  
       real user group id:1000  
     effective user group id:1000  

Note:
Process ID 0 is the id of scheduler process, often known as "swapper", it is part of the kernel.
Process ID 1 is the id of "init" process, and is invoked by the kernel at the end of bootstrap procedure.