The error_log file lists messages from the scheduler - errors, warnings, etc. The `LogLevel` directive controls which messages are logged:

level date-time message
I [20/May/1999:19:18:28 +0000] Job 1 queued on 'DeskJet' by 'mike'.
I [20/May/1999:19:21:02 +0000] Job 2 queued on 'DeskJet' by 'mike'.
I [20/May/1999:19:22:24 +0000] Job 2 was cancelled by 'mike'.

The level field contains the type of message:

- `A` - Alert message (LogLevel alert)
- `C` - Critical error message (LogLevel crit)
- `D` - Debugging message (LogLevel debug)
- `d` - Detailed debugging message (LogLevel debug2)
- `E` - Normal error message (LogLevel error)
- `I` - Informational message (LogLevel info)
- `N` - Notice message (LogLevel notice)
- `W` - Warning message (LogLevel warn)
- `X` - Emergency error message (LogLevel emerg)

The date-time field contains the date and time of when the page started printing. The format of this field is identical to the data-time field in the access_log file.

The message fields contains a free-form textual message. Messages from job filters are prefixed with "`[Job NNN]`".