I bet every time Iron Man does something in his suit, Jarvis makes a note of it. ‘Shot a Chitauri out of the ski’, ‘did a flip’, ‘took Pepper on a flight’. That way if something goes wrong, there’s a record of it. In the computing world, this is called logging.
Making a note every time a computer does something interesting is a good thing. If something breaks, you have notes that will hopefully let you figure out what happened. If every program on your computer logged differently, that would be a nightmare, especially if they all put their logs in different places. Troubleshooting would not be fun.
Instead, Linux® has a program that will do the logging for you. You just tell syslog what you want to log and how important it is. Then the syslog daemon will take care of everything for you. The importance of a message, also known as the priority, has several defined meanings.
From the syslog man page, we can see the list:
- LOG_EMERG system is unusable
- LOG_ALERT action must be taken immediately
- LOG_CRIT critical conditions
- LOG_ERR error conditions
- LOG_WARNING warning conditions
- LOG_NOTICE normal, but significant, condition
- LOG_INFO informational message
- LOG_DEBUG debug-level message
A message logged with the level LOG_EMERG means ‘Danger! Eek! Fix me now!’ or ‘It’s too late, we’re going down Iron Man!’. It can happen when the hard drive decides to fail dramatically. The syslog can scream ‘Dead Hard drive ahead!’ then fall over dead.
That’s not exactly what happens, but it sounds fun! My computer yelling ‘Dead Hard drive ahead!’ would certainly get my attention.
On the other end of the list is the LOG_DEBUG message. Debug messages are usually used by developers, that is, the people who make the programs that run on your system. The developers use them to debug, that is, find the bugs in their code. These aren’t literal bugs, of course, but rather things that are unexpectedly happening that shouldn’t be.
Actual bug not found in computer
Next time we’ll talk more about logging and syslog.