June 2017
Intermediate to advanced
478 pages
13h 14m
English
Content preview from Mastering Embedded Linux Programming - Second Edition
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Kernel messages
Kernel developers are fond of printing out useful information through liberal use of printk() and similar functions. The messages are categorized according to importance, with 0 being the highest:
| Level | Value | Meaning |
| KERN_EMERG | 0 | The system is unusable |
| KERN_ALERT | 1 | Action must be taken immediately |
| KERN_CRIT | 2 | Critical conditions |
| KERN_ERR | 3 | Error conditions |
| KERN_WARNING | 4 | Warning conditions |
| KERN_NOTICE | 5 | Normal but significant conditions |
| KERN_INFO | 6 | Informational |
| KERN_DEBUG | 7 | Debug-level messages |
They are first written to a buffer, __log_buf, the size of which is two to the power of CONFIG_LOG_BUF_SHIFT. For example, if CONFIG_LOG_BUF_SHIFT is 16, then __log_buf is 64 KiB. You can dump the entire buffer ...
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