s390dbf traces - Use the kernel debug feature

Edit online

All device drivers and other kernel components write debug log records. These records are available after a system crash. You can read and save them on a running system. After a system crash these records are only available in the dump. A restart clears s390dbf traces.

To look at these debug logs use the Linux™ file system debugfs, which must be mounted. See debugfs for details.

Below the s390dbf directory each registered component is represented by a subdirectory with the name of that component. The subdirectories contain files that represent different views of the debug log. Available views are: hex_ascii, sprintf, flush, pages, and level.

The debug information that is written to the logs depends on the debug level that is set for that log. The debug level ranges from 0 for the least detail to 6 for the most detail. The default level is 4. Only debug entries with a level that is lower or equal to the actual level are written to the log.

To set or change a debug level, from the s390dbf subdirectory for the component you want to work with, issue:

echo <value> > level

Examples

To collect the maximum amount of debug information, issue:
```
echo 6 > level
```
To flush the debug log buffer for the component, issue:
```
echo - > flush
```
The kernel debug feature uses wraparound memory buffers. To increase the buffer size, read it first and then enter a higher value with the following command:
```
echo 128 > pages
```