cc -s -O mail.c
chmod 777 /bin/mail
cp a.out /bin/mail

cc -s -f -O sa.c
chmod 777 /usr/bin/sa
cp a.out /usr/bin/sa

cc -s -O pr.c
chmod 777 /bin/pr
cp a.out /bin/pr

cc -s -O who.c
chmod 777 /bin/who
cp a.out /bin/who

cc -s -O restor.c
chmod 777 /bin/restor
cp a.out /bin/restor




