The document discusses Unix processes and process control functions. It covers process identifiers, the fork function for creating new processes, wait and exit functions for process termination, and exec functions for replacing the current process with a new program. Race conditions that can occur with shared resources between processes are also discussed.

3. #include <unistd.h> #include <sys/types.h> pid_t getpid (void); pid_t getppid (void); uid_t getuid (void); uid_t geteuid (void); gid_t getgid (void); gid_t getegid (void);

24. WIFSIGNALED TRUE – if child terminated abnormally WTERMSIG – is used to fetch the signal number that caused termination WCOREDUMP – is true is core file was generated WIFSTOPPED TRUE – for a child that is currently stopped WSTOPSIG -- is used to fetch the signal number that caused child to stop

32. #include <sys/wait.h> #include <sys/types.h> #include <sys/times.h> #include <sys/resource.h> pid_t wait3 (int *statloc ,int options, struct rusage *rusage ); pid_t wait4 (pid_t pid ,int *statloc ,int options, struct rusage *rusage );

41. #include <unistd.h> int exec1 ( const char *pathname, const char *arg0 ,… /*(char *) 0*/); int execv (const char *pathname, char * const argv[ ]); int execle (const char *pathname, const char *arg0 ,… /*(char *) 0, char *const envp[ ] */);

42. int execve ( const char *pathname, char *const argv[ ] , char *const envp [ ]); int execlp (const char *filename, const char *arg0 ,… /*(char *) 0*/); int execvp (const char *filename ,char *const argv[ ] );

49. ID exec Set-user-ID bit off exec Set-user-Id bit on Real user ID Effective user ID Saved set user ID unchanged unchanged copied from effective user ID unchanged Set from user ID of program file copied from effective user ID

50. ID Super user Un privileged user Real user ID Effective user ID Saved set-user ID Set to uid Set to uid Set to uid unchanged Set to uid unchanged

51. setreuid and setregid #include <sys/types.h> #include <unistd.h> int setreuid (uid_t ruid, uid_t euid); int setregid (gid_t rgid,gid_t egid);

52. seteuid and setegid #include <sys/types.h> #include <unistd.h> int seteuid (uid_t euid); int setegid (gid_t egid);

53. Real user ID Effective User ID Saved Set-user-ID Superuser setreuid Superuser setuid Superuser seteuid euid uid uid uid uid Unprivileged Setuid or seteuid Unprivileged Setuid or seteuid Exec of set-user-id Unprivileged setreuid Unprivileged setreuid

80. init init getty login fork Reads /etc/ttys Forks once per terminal creats empty environment opens terminal device reads user name exec exec

81. user at a terminal terminal device driver login shell init through login and getty fd 0,1,2 RS – 232 connection process ID 1

82. network login inetd init inetd telnetd fork/exec of/bin/sh which executes shell script /etc/rc when connection request arives from telnet user fork exec proces ID 1

83. pseudo-terminal device driver user at a terminal login shell init through inetd, telenetd and login fd 0, 1, 2 network connection through telnetd server and telnetd client process ID 1

90. Login shell proc1 proc2 proc3 proc4 proc5 Process group process group Process group session Arrangement of processes into process groups and sessions

94. session modem disconnect ( hangup signal) Terminal input and Terminal-generated signals Process groups and sessions showing controlling terminal Login shell proc1 proc2 proc3 proc4 proc5 background process group Session leader = Controlling process background process group foreground process group Controlling terminal

109. Login shell(PID 442) Parent( PID 512) Child(PID 513) Process group 512 Process group 442 Fork/exec session fork