./skript.sh user
#!/bin/bash
user=${1:-guest}
whoami
sudo -u "$user" whoami
exit 0
[guest@localhost sh]$ ./t.sh guest
guest
guest
[guest@localhost sh]$ ./t.sh apache
guest
apache
[guest@localhost sh]$
А т.к. он должен запускаться из крона
# m h dom mon dow user command
sudo -u user /home/script.sh