nginx gave a "502 Bad Gateway".

```

systemctl status munin-graph

× munin-graph.service - Munin FastCGI Graph Loaded: loaded (/etc/systemd/system/munin-graph.service; static) Active: failed (Result: exit-code) since Fri 2023-12-08 08:29:38 CET; 17s ago Duration: 531ms TriggeredBy: × munin-graph.socket Process: 155856 ExecStart=/usr/lib/munin/cgi/munin-cgi-graph (code=exited, status=28) Main PID: 155856 (code=exited, status=28) CPU: 527ms

Dec 08 08:29:37 dojo systemd[1]: Started munin-graph.service - Munin FastCGI Graph. Dec 08 08:29:38 dojo munin-cgi-graph[155856]: Fontconfig error: No writable cache directories ```

Solution:

1. Free space on /var partition (was full)
2. Run fc-cache --force