Every error (E) and warning (W) the radio has logged — the same lines the serial console shows, kept on the device so you do not need a cable to see them. A === boot === line marks each start and says how the previous one ended.

The log survives a restart and a crash, but not a power cut or a firmware update. It holds the last ~32 KB; older lines drop off by themselves. Keys, tokens and passwords in URLs are masked, so the file is safe to attach to a bug report.