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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. |