Working with the Unix OS

Processes I
}
printf("%d %s\n", cntr, argv[cntr]);
}
cntr = 0;
while(envp[cntr] [0] != 0)
{
printf( "%s\n", envp[cntr]);
cntr++;
}
testenv output
0 a.out
-= ./a/out
FCEDIT=/usr/bin/vi
EXINIT=set dir=/tmp
HOME=/staff/tech/greg
PWD=/staff/tech/greg/itb443
SHELL=/bin/ksh
MAIL=/usr/mail/greg
EDITOR=vi
TERMCAP=/etc/termcap
LOGNAME=greg
TERM=vt100
PATH=/usr/bin:/usr/local/bin:/bin:/usr/lib …>
TZ=est10
exit system call
void exit (status)/* does NOT */
int status; /* return */
convention: 0 normal termination
!= 0 abnormal termination
[a child process's 'parent-pid' changes to 1 (1 = init process) on parent termination]
The exiting process's parent receives the status via 'wait'
wait system call
int wait(status)
int *status;
/* returns process-id of child or –1 on error(no children)
and status-code into *status unless status = NULL */
Zombie: exit by child before wait by parent; zombie retains only process (system) descriptor info till waited.
Orphan: parent terminates before child does ... child gets new 'parent-process id' of 1.
wait (status)
if *status.lbyte = 0
then *status.rbyte is child's exiting status-code, i.e. as in "exit(n);"
Pipes
- accessed via std i/f (i.e. via file descriptor)
- each pipe associated with an inode (in table)
- size: 10 blocks = 5120 bytes (>4096)
- non-blocking read, blocking write (full)
Must check no. of bytes read in. If it is not blocking it will just return fewer bytes than requested.
Pipe creation
int fd[2]; pipe(fd);
/* fd[0] for reading
96