Question 1

How do I set up basic logging in a Rust executable using log?

Accepted Answer

Add log and a backend like env_logger to your Cargo.toml, then early in main, initialize the logger with e.g., env_logger::init(). This enables log macros to output messages based on the backend's configuration.

Question 2

What's the difference between log and tracing in Rust?

Accepted Answer

log is a simple facade for traditional leveled logging, ideal for basic needs and library compatibility. tracing offers advanced features like spans and context propagation for distributed systems observability, so choose log for simplicity or tracing for complex monitoring.

Question 3

How can I enable structured logging with the log crate?

Accepted Answer

Enable the `kv` feature in your Cargo.toml under log dependencies. Then, use the extended macro syntax with key-value pairs, like `info!(key:value; 'message')`, to attach structured data as shown in the README's structured logging example.

Question 4

Which logger backend is best for production Rust applications?

Accepted Answer

It depends: env_logger is simple and popular for development; log4rs offers rich configuration for production; syslog or systemd-journal-logger integrate with system logging. Evaluate based on performance, features, and deployment environment.

Question 5

Why are my log messages not showing up in Rust?

Accepted Answer

This usually happens if the logger isn't initialized—ensure you call the backend's init function early in main. Also, check log levels; backends like env_logger default to showing only info and above, which you can adjust via environment variables.

Question 6

How to change log levels dynamically at runtime with log?

Accepted Answer

log itself doesn't provide dynamic level changes; you need a backend that supports it. For example, with env_logger, use the RUST_LOG environment variable, or with log4rs, reload configuration files to update levels without restarting.

Question 7

Can I use log in WebAssembly projects?

Accepted Answer

Yes, use the console_log backend which logs to the browser's console. Add console_log to your dependencies, initialize it in your WASM code, and log messages will appear in the browser's developer tools, as noted in the README's WebAssembly section.

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