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I can however, give a bit of context about how the those shared memory allocations are used within the scope of LTTng. These shared memory sections are used for presence/absence notifications between lttng-sessiond and applications instrumented with LTTng-UST. `lttng-ust-wait-8` is intended to be used for applications that are running as root, or those run as non-root users that are members of the tracing group (if configured). `lttng-ust-wait-8-NNN` is used for non-root instrumented applications where NNN is the UID of the user. When either lttng-sessiond or an application instrumented with lttng-ust starts, the shared memory sections will be allocated. There is special treatment for `lttng-ust-wait-8` since it may be used to notify non-root applications that are run by users that are members of the tracing group. In that case, it is created with an extended mode[1], as you are observing. Those permissions are updated when there is a root lttng-sessiond that starts and opens or creates a shared memory section at the same path[2]. On 3/10/25 10:12 AM, bill robertson via lttng-dev wrote: > GHA runners appear to use lttng-ust for some sort of IPC between runners on > the same machine. > > $ ll /dev/shm/ > > -rw-rw-rw- 1 gha-runner-7 gha-runner-7 4096 Feb 20 04:03 lttng-ust-wait-8 > -rw-r----- 1 gha-runner-8 gha-runner-8 4096 Feb 20 04:03 lttng-ust-wait-8-558 > -rw-r----- 1 gha-runner-7 gha-runner-7 4096 Feb 20 04:03 lttng-ust-wait-8-559 > -rw-r----- 1 gha-runner-6 gha-runner-6 4096 Feb 20 04:03 lttng-ust-wait-8-560 > -rw-r----- 1 gha-runner-5 gha-runner-5 4096 Feb 20 04:03 lttng-ust-wait-8-561 > -rw-r----- 1 gha-runner-4 gha-runner-4 4096 Feb 20 04:03 lttng-ust-wait-8-562 > -rw-r----- 1 gha-runner-3 gha-runner-3 4096 Feb 20 04:03 lttng-ust-wait-8-563 > -rw-r----- 1 gha-runner-2 gha-runner-2 4096 Feb 20 04:03 lttng-ust-wait-8-564 > -rw-r----- 1 gha-runner-1 gha-runner-1 4096 Feb 20 04:03 lttng-ust-wait-8-565 > > > I assume that this is their code, and not some configuration issue on the > host machine, but if this may not be the case, can someone explain what can > be done or point me to information on the subject? Could you clarify what you are trying to achieve? > > Otherwise, is there some sort of environment variable or other setting that > lttng will reference when creating this shared memory section such that it > is not world-writable? All of the runners run under user accounts that are > in a common group. In LTTng-UST 2.14+, setting `LTTNG_UST_APP_PATH`[3] will disable connections to root (global) lttng-sessionds for instrumented applications. > > Thanks! > Bill > [1]: https://github.com/lttng/lttng-ust/blob/ce89cb05f0fc02b68396220815070996fa0bb4a5/src/lib/lttng-ust/lttng-ust-comm.c#L1705 [2]: https://github.com/lttng/lttng-tools/blob/e995b146f3456dd51fd76288db6dae9efdbce592/src/common/shm.cpp#L118 [3]: https://github.com/lttng/lttng-ust/blob/ce89cb05f0fc02b68396220815070996fa0bb4a5/src/lib/lttng-ust/lttng-ust-comm.c#L611C9-L611C27