Unix System Programming Notes

1.The most privileged user superuser or root, has a user ID of 0.The root user is usually the system administrator.

2.The process uses the effective IDs for determining access permission for files.

#include <unistd.h>

gid_t   getegid(void);

gid_t   geteuid(void);

gid_t   getgid(void);

gid_t   getuid(void);

pid_t  getpid(void);

pid_t getppid(void);

None of these functions can return an error.