Hello,

the issue is blocked alsa audio on login to desktop,
audio playback attempts of various programs fail with error messages:

* "unable to create IPC semaphore" and
* "ALSA: Couldn't open audio device: Permission denied"

example: aplay /usr/share/sounds/alsa/Noise.wav

ALSA lib pcm_direct.c:2178:(_snd_pcm_direct_new) unable to create IPC semaphore
aplay: main:850: audio open error: Permission denied


the problem appeared on 04.03.2024,
probably on first system boot after "aptitude safe-upgrade" from previous day.


I noticed lightdm is using alsa ipc key:

cat /usr/share/alsa/alsa.conf | grep ipc_

defaults.pcm.ipc_key 5678293
defaults.pcm.ipc_gid audio
defaults.pcm.ipc_perm 0660

note: 5678293 == 0x0056a4d5


==
== ipcs before login to desktop
==
------ Message Queues --------
key        msqid      owner      perms      used-bytes   messages

------ Shared Memory Segments --------
key        shmid      owner      perms      bytes      nattch     status
0x0056a4d5 0          lightdm    660        488        1
0x0056a4d6 1          lightdm    660        131072     1
0x00000000 5          lightdm    600        524288     2          dest

------ Semaphore Arrays --------
key        semid      owner      perms      nsems
0x0056a4d5 0          lightdm    660        1


==
== ipcs when logged in to desktop, audio playback is blocked
==

------ Message Queues --------
key        msqid      owner      perms      used-bytes   messages

------ Shared Memory Segments --------
key        shmid      owner      perms      bytes      nattch     status
0x0056a4d5 0          lightdm    660        488        0
0x0056a4d6 1          lightdm    660        131072     0
0x00000000 6          wwa        600        393216     2          dest
0x00000000 9          wwa        600        524288     2          dest
0x00000000 12         wwa        600        393216     2          dest

------ Semaphore Arrays --------
key        semid      owner      perms      nsems
0x0056a4d5 0          lightdm    660        1


==
== workaround:
==

 executing speaker-test (on any other program playing audio) as root
 solves the problem until user's logout back to lightdm.

==
== ipcs after running speaker-test once as root, alsa audio works again for normal user
==

------ Message Queues --------
key        msqid      owner      perms      used-bytes   messages

------ Shared Memory Segments --------
key        shmid      owner      perms      bytes      nattch     status
0x00000000 6          wwa        600        393216     2          dest
0x00000000 9          wwa        600        524288     2          dest
0x00000000 12         wwa        600        393216     2          dest

------ Semaphore Arrays --------
key        semid      owner      perms      nsems

Dear Maintainer,

the issue has been apparently resolved by a recent (2025-03-22) apt update.
(it was probably some of lightdm's dependencies)