Linux with Operating System Concepts

PROBLEM 5: SCHEDULED EVENT DID NOT TAKE PLACE
Description: An event scheduled through crontab, at, batch, or anacron did not take place 
as expected.
Steps to determine the problem:
1. Examine the cron log file to see if the event took place.
2. See if system downtime occurred when the event was scheduled.
3. Check to see if the event took place at the next boot (via anacron).
4. Check to see if the event failed because the scheduler did not have adequate 
permission.
5. See if the event took place but generated an error, through the audit or cron log.
Short-term solution: Reexecute the scheduled event.
Long-term solution: Move the event from cron to anacron. Change the scheduled event 
date and time. If a user needs permission to run cron or at jobs, add the user to /etc/at.allow 
and/or /etc/cron.allow.
PROBLEM 6: NETWORK NOT RESPONDING
Description: You are unable to reach other computers via your web browser or other net-
work tools.
Steps to determine the problem:
1. See if the network service is running.
2. Use ip to check the status of your interface device(s), do you have MAC addresses? IP 
addresses? Do you have a router or gateway connection?
3. Check the physical connection to the network to see if there is something wrong with 
the cable or port.
4. Use ping and/or traceroute to see if you can reach your gateway. If successful, use 
ping/traceroute to reach a computer on your local area network and then a computer 
on the Internet.

---

Maintaining and Troubleshooting Linux
◾
611
5. Test to see if you can reach computers using IP addresses but not IP aliases (check 
your resolv.conf file).
6. See if other users are also unable to communicate via the network.
Short-term solution: Restart the network service. Check your network configuration 
files (e.g., ifcfg-eth0). If you are using DHCP, make sure your DHCP server is respond-
ing. Make sure your name servers are responding. If they are unavailable, you may still 
be able to reach the network using IP addresses (instead of aliases), or place the mapping 
information in your /etc/hosts file. If none of this works, reboot your computer. Reboot 
the DHCP server.
Long-term solutions: Reconfigure the network itself by replacing the DHCP server and/
or network gateway. Test your network cables. Try an alternate network interface device 
(e.g., replace your Ethernet card with a new one).