jellyfin/debian/conf/logging.json

{
    "Serilog": {
        "MinimumLevel": "Information",
        "WriteTo": [
            { "Name": "Console",
                "Args": {
                    "outputTemplate": "[{Timestamp:HH:mm:ss}] [{Level:u3}] {Message:lj}{NewLine}{Exception}"
                }
            },
            { "Name": "File",
                "Args": {
                    "path": "%JELLYFIN_LOG_DIR%//jellyfin.log",
                    "fileSizeLimitBytes": 10485700,
                    "rollOnFileSizeLimit": true,
                    "retainedFileCountLimit": 10,
                    "outputTemplate": "[{Timestamp:yyyy-MM-dd HH:mm:ss.fff zzz}] [{Level:u3}] {Message}{NewLine}{Exception}"
                }
            }
        ]
    }
}