## Overview

This module provides APIs to log information when running applications.

A sample log message logged from the `foo` module would look as follows:
```bash
time = 2021-05-12T11:20:29.362+05:30 level = ERROR module = myorg/foo message = "Something went wrong"
```

### Log Levels

The `log` module provides APIs to log at four levels, which are `DEBUG`, `ERROR`, `INFO`, and `WARN`. By default, all log messages are logged to the console at the `INFO` level.

The log level can be configured via a Ballerina configuration file.
To set the global log level, place the entry given below in the `Config.toml` file:

```
[ballerina.log]
level = "[LOG_LEVEL]"
```

Each module can also be assigned its own log level. To assign a log level to a module, provide the following entry in the `Config.toml` file:

```
[[ballerina.log.modules]]
name = "[ORG_NAME]/[MODULE_NAME]"
level = "[LOG_LEVEL]"
```

### Log Output

Logs are written to the `stderr` stream by default.

To publish the logs to a file, redirect the `stderr` stream to a file as follows.
```bash
$ bal run program.bal 2> b7a-user.log
```

By default, logs are printed in the `LogFmt` format. To set the output format to JSON, place the entry given below in the `Config.toml` file.

```
[ballerina.log]
format = "json"
```

A sample log message logged from the `foo` module in JSON format would look as follows:
```bash
{"time":"2021-05-12T11:26:00.021+05:30", "level":"INFO", "module":"myorg/foo", "message":"Authenticating user"}
```

For information on the operations, which can be performed with the log module, see the below **Functions**.


Represents file opening options for writing.



Overwrite(truncate the existing content)


OVERWRITE

APPEND

FileWriteOption

Error

Prints debug logs.
```ballerina
log:printDebug("debug message", id = 845315)
```



printDebug

string

'error

error

keyValues

KeyValues

Prints error logs.
```ballerina
error e = error("error occurred");
log:printError("error log with cause", 'error = e, id = 845315);
```



printError

Prints info logs.
```ballerina
log:printInfo("info message", id = 845315)
```



printInfo

Prints warn logs.
```ballerina
log:printWarn("warn message", id = 845315)
```



printWarn

Set the log output to a file. Note that all the subsequent logs of the entire application will be written to this file.
```ballerina
var result = log:setOutputFile("./resources/myfile.log");
var result = log:setOutputFile("./resources/myfile.log", log:OVERWRITE);
```



setOutputFile

path

To indicate whether to overwrite or append the log output


option

A `log:Error` if an invalid file path was provided


Key-Value pairs that needs to be desplayed in the log.



never

Value

This module provides APIs to log information when running applications.


Types