Errors

Review

General Troubleshooting Strategies

• Do things work as expected?

• If so, move on.
• If not, how can I find out what went wrong?

• Is there something in the system logs?
• Are there any application specific logs?
• If there are no logs, are there any commands that I can do to narrow down the error scope?
• Could there be other problems that would affect this (i.e. disk full, other system issues)(firewall?)

General Troubleshooting Strategies

• Other avenues of support?

• GOOGLE!
• forums, discussions,
• peers, colleagues

DNS Troubleshooting Strategies

• Dig, dig, dig.

• Start at root
• Travel down the hierarchy
• Test from localhosts, remote hosts
• inside network, outside network
• test master and slave

DNS Troubleshooting Strategies

• What do the logs say about it?
• Was the zone transferred successfully?

• Does it say something about a failure on any line?

• If digs against slave aren't working, your transfer probably didn't complete!

DNS Common Problems

• Typos in zone or named.conf.local

• Dots?? (after NS records, at end of ptr record, end of SOA lines)
• Semicolons
• OTher syntax errors

• I can't wget
• My slave isn't working

• Misconfigured named.conf.local

• TTL set too high, you have to wait a long time for new refresh.
• A record pointed to wrong host.

DNS Common Problems

• Conceptual understanding
  • What does delegate mean?
  • Are you blindly following slides or do you try to understand what they are saying?
  • For the exam, it will be VERY difficult to rely on slides to tell you what to do, though it is open note.

Database Troubleshooting Strategies

• Can you login from localhost?
  • See the database?
• Can you login from remote host?
  • by ip vs fqdn?
  • See the database?
• What does the mysql.error log have to say?

Database Common Problems

• System level users vs Database users
  • They are not the same!
• Most problems boil down to:
  • Did you create the database
  • Did you execute the correct GRANT statement on the database
  • Did we allow remote connections?
• Examples:
  • GRANT ALL PRIVILEGES ON 'foo'.'*' to 'bob'@'144.38.195.%' IDENTIFIED BY 'secret';
  • GRANT ALL PRIVILEGES ON 'foo'.'*' to 'bob'@'144.38.196.%' IDENTIFIED BY 'cows';
  • GRANT ALL PRIVILEGES ON 'foo'.'*' to 'bob'@'localhost' IDENTIFIED BY 'cows';

Email Troubleshooting Strategies

• Can you send an email to someone in the domain?
• Send out to world?
• Send from world back to domain?
• MX record found? (If not, fall back to A record)
  • You CAN do a dig test to see if it is working.
• Listening on ports (do a netstat -natp) (This is good for looking at ANY service)
• Logs?(Paniclog, mainlog?)

Email Common Problems

• Your DNS isn't working
• You don't have a user created

HTTP Troubleshooting Strategies

• Can you visit the website?
• Can you dig the FQDN and get an IP?
• If it shows a different page than what you were expecting:
  • DId you enable the virtual host?
  • DId you create the correct document root?
  • Is there content?

Filesystem Troubleshooting Strategies

• See the filesystem slides
• Remember the basic steps
  • partition
  • format
  • mount
  • create file

Other random problems

Most common source of errors in this class are typos in the SUBMISSION file!

Other common errors are permission issues:

• when mounting/creating files
• web applications/ web pages
• user no have perms to db

Fix by issuing new permissions or ownership commands:

• chmod
• chown
• grant (for mysql)

Other random problems (System related)

Sometimes different system settings are affecting our programs:

• incorrect IP, subnet mask, default gateway
• umask, UID, GID
• hostnames
  • /etc/hosts here
  • Does this have to match what is in DNS?
  • They absolutely SHOULD!
  • /etc/hostname
    • Does this need to match DNS?
    • Not really

Make sure your system is solid FIRST!