| 1 | --- |
| 2 | id: proc-lttng-logger-abi |
| 3 | --- |
| 4 | |
| 5 | The `lttng-tracer` Linux kernel module, installed by the LTTng-modules |
| 6 | package, creates a special LTTng logger ABI file `/proc/lttng-logger` |
| 7 | when loaded. Writing text data to this file generates an LTTng kernel |
| 8 | domain event named `lttng_logger`. |
| 9 | |
| 10 | Unlike other kernel domain events, `lttng_logger` may be enabled by |
| 11 | any user, not only root users or members of the tracing group. |
| 12 | |
| 13 | To use the LTTng logger ABI, simply write a string to |
| 14 | `/proc/lttng-logger`: |
| 15 | |
| 16 | <pre class="term"> |
| 17 | echo -n 'Hello, World!' > /proc/lttng-logger |
| 18 | </pre> |
| 19 | |
| 20 | The `msg` field of the `lttng_logger` event contains the recorded |
| 21 | message. |
| 22 | |
| 23 | <div class="tip"> |
| 24 | <p> |
| 25 | <span class="t">Note:</span>Messages are split in chunks of |
| 26 | 1024 bytes. |
| 27 | </p> |
| 28 | </div> |
| 29 | |
| 30 | The LTTng logger ABI is a quick and easy way to trace some events from |
| 31 | user space through the kernel tracer. However, it is much more basic |
| 32 | than LTTng-UST: it's slower (involves system call round-trip to the |
| 33 | kernel and only supports logging strings). The LTTng logger ABI is |
| 34 | particularly useful for recording logs as LTTng traces from shell |
| 35 | scripts, potentially combining them with other Linux kernel/user space |
| 36 | events. |