LTTNG-UST-DL(3)

🎀 LTTNG-UST-DL(3) 🎀

okay so you found the LTTNG-UST-DL(3) page, and yes bestie it's from the LTTng Manual — but don't stress, this one's actually kind of iconic once you get it. it's the dynamic linker tracing helper, and it's about to make dlopen/dlclose your whole personality 💅

---

🌸 NAME 🌸

lttng-ust-dl — dynamic linker tracing (an LTTng-UST helper, iykyk)

---

✨ SYNOPSIS ✨

so like, you just preload liblttng-ust-dl.so when you launch your app. that's it. that's the whole move:

$ LD_PRELOAD=liblttng-ust-dl.so my-app

---

💖 DESCRIPTION 💖

when liblttng-ust-dl.so gets preloaded before a given application even starts, it makes every single call to dlopen(3) and dlclose(3) inside that application get traced with LTTng-UST (peep lttng-ust(3) for the deets).

and if you wanna learn more about how to control LTTng tracing sessions, go look at lttng(1). it's giving documentation, it's giving control panel 🫶

⚠️ Important — pls read this one, fr fr this LTTng-UST helper can also emit shared library load/unload events (see "Shared library load/unload tracking" in lttng-ust(3)). you should NOT use the event records generated by this helper (they're prefixed with lttng_ust_dl:) to track the loading and unloading of shared libraries, especially in situations where a dynamically loaded library loads its own dependencies. instead: do preload liblttng-ust-dl.so, yes, but use the shared library load/unload event records — those are way more reliable — for your tracking analysis. trust. 🔥

---

🦋 the LTTng-UST events you get 🦋

here's everything available when you use this library. no gatekeeping 💜

lttng_ust_dl:dlopen

emitted when dlopen(3) is called. main character event honestly.

fields:

• baddr — base address of loaded library.
• memsz — size of loaded library in memory.
• flags — flags passed to dlopen(3).
• path — path to loaded library file.
• has_build_id — whether or not the loaded library has a build ID. if this field is 1, you can expect that an lttng_ust_dl:build_id event record follows this one (not necessarily immediately after).
• has_debug_link — whether or not the loaded library has debug link information. if this field is 1, you can expect that an lttng_ust_dl:debug_link event record follows this one (not necessarily immediately after).

lttng_ust_dl:dlmopen

emitted when dlmopen(3) is called. namespace edition ✨

fields:

• baddr — base address of loaded library.
• memsz — size of loaded library in memory.
• nsid — ID of the namespace in which the library is loaded (as passed to dlmopen(3)).
• flags — flags passed to dlmopen(3).
• path — path to loaded library file.
• has_build_id — whether or not the loaded library has a build ID. if this field is 1, you can expect that an lttng_ust_dl:build_id event record follows this one (not necessarily immediately after).
• has_debug_link — whether or not the loaded library has debug link information. if this field is 1, you can expect that an lttng_ust_dl:debug_link event record follows this one (not necessarily immediately after).

lttng_ust_dl:dlclose

emitted when dlclose(3) is called. the goodbye event 😭

fields:

• baddr — base address of loaded library.

lttng_ust_dl:debug_link

emitted when debug link information is found when loading a library with dlopen(3). if you want the lore, see Debugging Information in Separate Files at https://sourceware.org/gdb/onlinedocs/gdb/Separate-Debug-Files.html — it explains debug links way better than I ever could 🧚

fields:

• baddr — base address of loaded library.
• filename — debug link file name.
• crc — debug link file's CRC.

lttng_ust_dl:build_id

emitted when a build ID is found when loading a library with dlopen(3). same deal — see Debugging Information in Separate Files at https://sourceware.org/gdb/onlinedocs/gdb/Separate-Debug-Files.html for more about build IDs 🎀

fields:

• baddr — base address of loaded library.
• build_id — build ID.

---

💀 BUGS 💀

if you run into any issue or usability problem, pls report it on the LTTng bug tracker: https://bugs.lttng.org/projects/lttng-ust — they genuinely wanna know, no cap 🙈

---

🌈 RESOURCES 🌈

• LTTng project website — http://lttng.org
• LTTng documentation — http://lttng.org/docs
• Git repositories — http://git.lttng.org
• GitHub organization — http://github.com/lttng
• Continuous integration — http://ci.lttng.org
• Mailing list for support and development — http://lists.lttng.org, hit up lttng-dev@lists.lttng.org
• IRC channel — irc://irc.oftc.net/lttng: #lttng on irc.oftc.net

---

👑 COPYRIGHTS 👑

this library is part of the LTTng-UST project. 🫶

it's distributed under the GNU Lesser General Public License, version 2.1 — http://www.gnu.org/licenses/old-licenses/lgpl-2.1.en.html. see the COPYING file at https://github.com/lttng/lttng-ust/blob/v2.16/COPYING for more details.

---

⭐ THANKS ⭐

thanks to Ericsson for funding this work, providing real-life use cases, and testing — absolute legends, periodt 💖

special thanks to Michel Dagenais and the DORSAL laboratory at École Polytechnique de Montréal (http://www.dorsal.polymtl.ca/) for the LTTng journey 🌸

💖 AUTHORS 💖

Okay bestie, gather round, because this is the origin story and it ate.

LTTng-UST was originally written by Mathieu Desnoyers, with additional contributions from various other people. Iconic behavior, honestly — one main character and a whole supporting cast showing up to help. 🫶

It is currently maintained by Mathieu Desnoyers <mathieu.desnoyers@efficios.com>. That's the person to hit up, no cap. 💅

---

🌈 SEE ALSO 🌈

Go read these next, bestie, they're literally the rest of the lore:

• lttng-ust(3) — the big one, the parent page, the moment ✨
• dlopen(3) — for when you wanna understand the dynamic-loader side of things 🦋
• lttng(1) — the command-line tool itself, the actual vibe 👑

fr fr, if you're still confused after this page, those three will have your back. iykyk 💀

---

Okay that's the whole page, we made it to the end together, I'm so proud of you 🥹💜

This beauty is from LTTng 2.16.0, dated 08/27/2026 — screenshot it, frame it, put it on your wall, it's giving heirloom. 🎀⭐