Synapse just stopped working

[proudhon]

After 3 years without a single problem my homeserver stopped working after a system reboot requested by a full system update.

Synapse is running on a Debian 11 vm.

This is systemctl status for the service:

● matrix-synapse.service - Synapse Matrix homeserver
     Loaded: loaded (/lib/systemd/system/matrix-synapse.service; enabled; vendor preset: enabled)
     Active: activating (start) since Thu 2024-01-04 19:24:44 UTC; 4s ago
    Process: 173730 ExecStartPre=/opt/venvs/matrix-synapse/bin/python -m synapse.app.homeserver --config-path=/etc/matrix-synapse/homeserver.yaml --config-path=/etc/mat>
   Main PID: 173761 (python)
      Tasks: 1 (limit: 2322)
     Memory: 76.2M
        CPU: 3.735s
     CGroup: /system.slice/matrix-synapse.service
             └─173761 /opt/venvs/matrix-synapse/bin/python -m synapse.app.homeserver --config-path=/etc/matrix-synapse/homeserver.yaml --config-path=/etc/matrix-synapse>

Jan 04 19:24:48 spartaco matrix-synapse[173761]:     _setup_stdlib_logging(config, log_config_path, logBeginner=logBeginner)
Jan 04 19:24:48 spartaco matrix-synapse[173761]:   File "/opt/venvs/matrix-synapse/lib/python3.9/site-packages/synapse/config/logger.py", line 239, in _setup_stdlib_log>
Jan 04 19:24:48 spartaco matrix-synapse[173761]:     _load_logging_config(log_config_path)
Jan 04 19:24:48 spartaco matrix-synapse[173761]:   File "/opt/venvs/matrix-synapse/lib/python3.9/site-packages/synapse/config/logger.py", line 296, in _load_logging_con>
Jan 04 19:24:48 spartaco matrix-synapse[173761]:     logging.config.dictConfig(log_config)
Jan 04 19:24:48 spartaco matrix-synapse[173761]:   File "/usr/lib/python3.9/logging/config.py", line 809, in dictConfig
Jan 04 19:24:48 spartaco matrix-synapse[173761]:     dictConfigClass(config).configure()
Jan 04 19:24:48 spartaco matrix-synapse[173761]:   File "/usr/lib/python3.9/logging/config.py", line 571, in configure
Jan 04 19:24:48 spartaco matrix-synapse[173761]:     raise ValueError('Unable to configure handler '
Jan 04 19:24:48 spartaco matrix-synapse[173761]: ValueError: Unable to configure handler 'file'

[proudhon]

Somehow log permission changed and that was causing the problem.