MySQL Reference Manual

Appendix A. Problems and Common Errors

This appendix lists some common problems and error messages that users have run into. You will learn how to figure out what the problem is, and what to do to solve it. You will also find proper solutions to some common problems.

How to Determine What Is Causing Problems

When you run into problems, the first thing you should do is find out which program/piece of equipment is causing problems:

• If you have one of the following symptoms, it is probably a hardware (like memory, motherboard, CPU, or hard disk) or kernel problem:

  • The keyboard doesn’t work. This can normally be checked by pressing Caps Lock. If the Caps Lock light doesn’t change you have to replace your keyboard. (Before doing this, you should try to reboot your computer and check all cables to the keyboard.)

  • The mouse pointer doesn’t move.

  • The machine doesn’t answer to a remote machine’s pings.

  • Different, unrelated programs don’t behave correctly.

  • If your system rebooted unexpectedly (a faulty user-level program should never be able to take down your system).

  In this case you should start by checking all your cables and run some diagnostic tool to check your hardware! You should also check if there are any patches, updates, or service packs for your operating system that could likely solve your problems. Check also that all your libraries (like glibc) are up to date.

  It’s always good to use a machine with ECC memory to discover memory problems early!

• If your keyboard is locked up, you may be able to fix this by logging into your machine from another machine and execute kbd_mode -a on it.

• Please examine your system log file (/var/log/messages or similar) for reasons for your problems. If you think the problem is in MySQL, you should also examine MySQL’s log files. See Section 4.9.3.

• If you don’t think you have hardware problems, you should try to find out which program is causing problems.

  Try using top, ps, taskmanager, or some similar program to check which program is taking all CPU or is locking the machine.

• Check with top, df, or a similar program if you are out of memory, disk space, open files, or some other critical resource.

• If the problem is some runaway process, you can always try to kill it. If it doesn’t want to die, there is probably a bug in the operating system.

If, after you have examined all other possibilities, you have concluded that it’s the MySQL server or a MySQL client that is causing the problem, it’s time to do a bug report for our mailing list or our support team. In the bug report, try to give a very detailed description of how the system is behaving and what you think is happening. You should also state why you think it’s MySQL that is causing the problems. Take into consideration all the situations in this appendix. State any problems exactly how they appear when you examine your system. Use the “cut and paste” method for any output and/or error messages from programs and/or log files!

Try to describe in detail which program is not working and all symptoms you see! We have in the past received many bug reports that just state “the system doesn’t work”. This doesn’t provide us with any information about what could be the problem.

If a program fails, it’s always useful to know:

• Has the program in question made a segmentation fault (core dumped)?

• Is the program taking up the whole CPU? Check with top. Let the program run for a while. It may be evaluating something heavy.

• If it’s the mysqld server that is causing problems, can you do mysqladmin -u root ping or mysqladmin -u root processlist?

• What does a client program say (try with mysql, for example) when you try to connect to the MySQL server? Does the client jam? Do you get any output from the program?

When sending a bug report, you should follow the outlines described in this manual. See Section 1.6.2.2.