Answer Posted / s.rajasekhar

at - executes single time
crontab- executes Multiple time.

at:If you want postpone the excution of process we can use
at command.but you should specify time for running process.

crontab:If you want run some jobs at daily or some times u
can keep those jobs in crontab file.those are cronjobs.

crontab -l:To open crontab file
crontab -e:To edit the crontab file
crontab -r:To remove the crontab file

* * * * * job name

star1:min(1 to 59)
star2:hour(0 to 23)
star3:day of the month(1 to 31)
star4:month(1 to 12)
star5:day of the week(0 to 6)

here zero indicates Sunday

15 05 * * 1-5 job schedule----->This job will run everyday
at 5:15am except Sunday.


Like this so many jobs we can keep in one crontab file.

When i run a programm of orphan process. Instead of getting child's parent (ppid)=1 ..i get 1400 and it varies as per system. How can i findthe right soluion??? My pgm: #include # include int main() { int pid; pid=fork(); if(pid < 0) {exit(-1);} else if(pid==0) { printf("Child Process is Sleeping ..."); sleep(10); printf("Orphan Child's Parent ID : %u ",getppid()); } else { printf("Parent Process Completed ... %u ",getpid()); exit(0); } return 0; } Output:

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