Working with the Unix OS

Processes II
/* background.c */
#include
main(int argc, char *argv[])
{
if(fork()== 0){ /* child */
execvp(argv[1], &argv[1]);}
fprintf(stderr, "could not execute %s\n", argv[1]);
}
background cc wait.c
ps
PID TT STAT TIME COMMAND
664 p1 S 0:00 -ksh (ksh)
710 p1 R 0:00 ps
715 p1 D 0:00 cc wait.c
/* redirect.c */
#include
#include
main(int argc, char *argv[])
{
int fd;
fd = open(argv[1], O_CREAT | O_TRUNC | O_WRONLY, 0600);
dup2(fd, 1); /* duplicate standard output */
close (fd) ; /* close original descriptor */
execvp(argv[2], fprintf(stderr, &argv[2]); "main - should never execute\n");
}
redirect ls.out ls -1
cat ls.out
SIGNALS
- terminates process and generates core file (dump)
- terminates process without core (quit)
- ignores and discard signal (ignore)
- suspends process (suspend)
- resumes process
/* alarm.c */
#include
main()
{
alarm(3); /* schedule an alarm in 3 secs */
printf("looping forever ...\n");
while (1);
fprintf(stderr, "should never execute\n");
}
/* handler.c */
#include
#include
int alarmflag = 0;
void alarmhandler();
main()
{
signal (SIGALRM, alarmhandler); /* signal handler */
alarm(3); /* schedule an alarm in 3 secs */
printf ("looping. . . \n") ;
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