> ## Documentation Index > Fetch the complete documentation index at: https://mintlify.com/freerdp/freerdp/llms.txt > Use this file to discover all available pages before exploring further. # Logging > Configure WLog, the hierarchical logging system used throughout FreeRDP and WinPR. ## Overview WLog is a configurable and flexible logging system used throughout WinPR and FreeRDP. The primary concept is a hierarchy of loggers that can be configured independently. Each logger is identified by a dotted name (e.g., `core.channel`, `com.freerdp.client.x11`) and inherits settings from its parent unless overridden. Configuration is done entirely through environment variables — no source changes are required. *** ## Log levels Levels are cumulative: setting a level includes all levels below it in the hierarchy. | Level | Description | | ------- | ---------------------------------------- | | `TRACE` | Print everything, including packet dumps | | `DEBUG` | Debug messages | | `INFO` | General information | | `WARN` | Warnings | | `ERROR` | Errors | | `FATAL` | Fatal problems | | `OFF` | Completely disable WLog output | *** ## Environment variables ### Core variables | Variable | Description | | --------------- | ----------------------------------------------------------------------------------------------------------- | | `WLOG_LEVEL` | The minimum level to output. Applies globally unless overridden by `WLOG_FILTER`. | | `WLOG_FILTER` | Comma-separated list of `:` pairs. Only matching loggers at the specified level are printed. | | `WLOG_PREFIX` | Format string controlling the prefix of every log line. See [Format specifiers](#format-specifiers). | | `WLOG_APPENDER` | Selects the output target. See [Appenders](#appenders). | ### File appender variables | Variable | Description | | ------------------------------------ | ------------------------------------------- | | `WLOG_FILEAPPENDER_OUTPUT_FILE_PATH` | Directory in which the log file is written. | | `WLOG_FILEAPPENDER_OUTPUT_FILE_NAME` | Name of the output log file. | ### Journald appender variable | Variable | Description | | ------------------ | ------------------------------------------------------------------- | | `WLOG_JOURNALD_ID` | Identifier used with the journal (defaults to the executable name). | ### UDP appender variable | Variable | Description | | ----------------- | ------------------------------------------------------------ | | `WLOG_UDP_TARGET` | Target in `host:port` format. Defaults to `127.0.0.1:20000`. | *** ## Format specifiers The `WLOG_PREFIX` variable controls what appears before each log message. Specifiers are prefixed with `%`. | Specifier | Description | | --------- | ------------- | | `%lv` | Log level | | `%mn` | Module name | | `%fl` | File name | | `%fn` | Function name | | `%ln` | Line number | | `%pid` | Process ID | | `%tid` | Thread ID | | `%yr` | Year | | `%mo` | Month | | `%dw` | Day of week | | `%hr` | Hour | | `%mi` | Minute | | `%se` | Second | | `%ml` | Millisecond | A maximum of 16 specifiers can be used in a single format string. ### Example prefix ```bash theme={null} WLOG_PREFIX="pid=%pid:tid=%tid:fn=%fn -" xfreerdp /v:192.168.1.100 ``` *** ## Appenders An appender defines where log output is written. Select one with `WLOG_APPENDER`. Writes to the console. On Android, `log_print` is used instead. **`outputstream` option values:** * `stdout` — write everything to stdout * `stderr` — write everything to stderr * `default` — errors and fatal messages go to stderr; everything else to stdout * `debug` — use debug output (Windows only; behaves like `default` on other platforms) ```bash theme={null} WLOG_APPENDER=CONSOLE xfreerdp /v:192.168.1.100 ``` Writes textual log output to a file. ```bash theme={null} WLOG_APPENDER=FILE \ WLOG_FILEAPPENDER_OUTPUT_FILE_PATH=/var/log \ WLOG_FILEAPPENDER_OUTPUT_FILE_NAME=freerdp.log \ xfreerdp /v:192.168.1.100 ``` Writes log data in a binary format file. ```bash theme={null} WLOG_APPENDER=BINARY \ WLOG_FILEAPPENDER_OUTPUT_FILE_PATH=/tmp \ WLOG_FILEAPPENDER_OUTPUT_FILE_NAME=freerdp.bin \ xfreerdp /v:192.168.1.100 ``` Sends log messages to a remote host over UDP. The default target is `127.0.0.1:20000`. ```bash theme={null} WLOG_APPENDER=UDP WLOG_UDP_TARGET=127.0.0.1:20000 xfreerdp /v:192.168.1.100 ``` Receive messages with netcat in a second terminal: ```bash theme={null} nc -u 127.0.0.1 -p 20000 -l ``` Outputs log messages to syslog. No additional options are available. ```bash theme={null} WLOG_APPENDER=SYSLOG xfreerdp /v:192.168.1.100 ``` Syslog support is optional and depends on build-time configuration. Outputs log messages to the systemd journal. ```bash theme={null} WLOG_APPENDER=JOURNALD WLOG_JOURNALD_ID=freerdp xfreerdp /v:192.168.1.100 ``` Read the journal: ```bash theme={null} journalctl -t freerdp -f ``` Journald support is optional. It requires building with `-DWITH_LIBSYSTEMD=ON`. *** ## Filtering specific modules Use `WLOG_FILTER` to restrict output to particular loggers and levels. The format is a comma-separated list of `:` pairs. ```bash theme={null} # Show DEBUG messages for the core channel logger and TRACE for a specific component WLOG_FILTER=core.channel:DEBUG,dummy:TRACE xfreerdp /v:192.168.1.100 ``` Only loggers matching the filter are printed; all others are suppressed regardless of `WLOG_LEVEL`. *** ## Common recipes ```bash Enable TRACE logging globally theme={null} WLOG_LEVEL=TRACE xfreerdp /v:192.168.1.100 ``` ```bash Log to a file at DEBUG level theme={null} WLOG_LEVEL=DEBUG \ WLOG_APPENDER=FILE \ WLOG_FILEAPPENDER_OUTPUT_FILE_PATH=/tmp \ WLOG_FILEAPPENDER_OUTPUT_FILE_NAME=freerdp-debug.log \ xfreerdp /v:192.168.1.100 ``` ```bash Stream logs over UDP with netcat theme={null} # Terminal 1 - receive nc -u 127.0.0.1 -p 20000 -l # Terminal 2 - connect with UDP logging WLOG_APPENDER=UDP WLOG_LEVEL=DEBUG xfreerdp /v:192.168.1.100 ``` ```bash Verbose prefix with PID, TID, and function name theme={null} WLOG_PREFIX="pid=%pid:tid=%tid:fn=%fn -" WLOG_LEVEL=DEBUG xfreerdp /v:192.168.1.100 ```