Overview System Log

The log information is categorized into eight levels, including: emergencies, alerts, critical, errors, warnings, notifications, informational, and debugging. Here levels 0-6 are log information and level 2 is debugging information. For details, refer to the following table.

Table 9-1 Description of the System Log Level Fields

The log information is outputted to five directions: control console (Console terminal), monitor console (Telnet or SSH terminal), log server, log files (memory log files and flash log files), and email. The output to the five directly is controlled by respective configuration commands. The debugging information is outputted to two directions, control console and monitor console. The log information can also be configured to output to the log server or log files.

Table 9-2 Log Output Directions

The log module runs in a separate syslog process. The main thread of the syslog process receives the log information sent by the system. Firstly, process the log data and distribute the cache space. Then, load the configured output actions to the corresponding buffer queue of each output terminal. Because of the length limitation of the cache queue, when a large number of log information is output, there is a loss of log information. At this time, the log module will count the lost messages. There are two threads in the output of log scheduling (when the log information is output to the console, monitor, log server, run in the same sub-thread as log files; when the log information is output to email, run in another sub-thread). In the scheduling thread, enable a timer for each output direction, and after responding each time, the timer gets the log information data from the queue corresponding to the terminal and outputs to the corresponding terminal according to the user configuration.