| 1 | --- |
| 2 | id: lttng-ust-environment-variables-compiler-flags |
| 3 | --- |
| 4 | |
| 5 | A few special environment variables and compile flags may affect the |
| 6 | behavior of LTTng-UST. |
| 7 | |
| 8 | LTTng-UST's debugging can be activated by setting the environment |
| 9 | variable `LTTNG_UST_DEBUG` to `1` when launching the application. It |
| 10 | can also be enabled at compile time by defining `LTTNG_UST_DEBUG` when |
| 11 | compiling LTTng-UST (using the `-DLTTNG_UST_DEBUG` compiler option). |
| 12 | |
| 13 | The environment variable `LTTNG_UST_REGISTER_TIMEOUT` can be used to |
| 14 | specify how long the application should wait for the |
| 15 | [session daemon](#doc-lttng-sessiond)'s _registration done_ command |
| 16 | before proceeding to execute the main program. The timeout value is |
| 17 | specified in milliseconds. 0 means _don't wait_. -1 means |
| 18 | _wait forever_. Setting this environment variable to 0 is recommended |
| 19 | for applications with time contraints on the process startup time. |
| 20 | |
| 21 | The default value of `LTTNG_UST_REGISTER_TIMEOUT` (when not defined) |
| 22 | is **3000 ms**. |
| 23 | |
| 24 | The compilation definition `LTTNG_UST_DEBUG_VALGRIND` should be enabled |
| 25 | at build time (`-DLTTNG_UST_DEBUG_VALGRIND`) to allow `liblttng-ust` |
| 26 | to be used with <a href="http://valgrind.org/" class="ext">Valgrind</a>. |
| 27 | The side effect of defining `LTTNG_UST_DEBUG_VALGRIND` is that per-CPU |
| 28 | buffering is disabled. |