How to enable logging

When troubleshooting issues, a debug log can provide valuable information. This guide explains how to enable logging in Chrome and Chromium to generate a log file that you can attach to a bug report.

How to Collect a Debug Log File

To create a log file, you need to launch the browser with a specific command-line flag. This will create a file named chrome_debug.log on your computer.

On Windows

1. Close any running instances of the browser.
2. Launch the Command Prompt and run the following command.

path\to\chrome.exe --enable-logging --v=1

On Mac and Linux

1. Close any running instances of the browser.
2. Launch the Terminal and run the following command:

/path/to/chrome --enable-logging --v=1

On these platforms, this command will create the log file in your user data directory and will not print output to the terminal.

Finding the Log File (chrome_debug.log)

After running the browser with logging enabled, the chrome_debug.log file will be created. It is overwritten each time you restart the browser. Here’s where to find it:

• Release builds: In the user data directory, which is the parent directory of the Default/ profile folder.
• Debug builds: In the build output directory (e.g., out/Debug).
• Chrome OS:
  • Logs are available in /var/log/chrome/.
  • At the login screen, they can be found in /var/log/ui/.
  • For more details, see the Chrome OS debugging guide.

Controlling Verbosity

You can control the level of detail in the logs with these flags:

• --v=N: Sets the default maximum active V-logging level; 0 is default. Any VLOG(x) with x <= N will be displayed. 1 is a good level for bug reports.
• --vmodule=module1=N,module2=M,...: Overrides the V-logging level for specific modules. For example, --vmodule=metrics=2 enables verbose logging for code in files named metrics.*. Wildcards are supported, e.g., --vmodule=*/metrics/*=2. See details in base/logging.h. You can add --v=-1 to suppress all other logging.

Advanced: Viewing Logs in Real-Time (stderr)

For developers who want to see log output directly in the terminal, you can direct the logs to standard error (stderr). This is useful for live debugging but is not ideal for creating a log file for a bug report.

On Linux and Mac

/path/to/chrome --enable-logging=stderr --v=1

This will print log messages to your terminal. You can also redirect this output to a file:

/path/to/chrome --enable-logging=stderr --v=1 > log.txt 2>&1

On Windows

On Windows, logging to stderr is possible, but output from sandboxed renderer processes will not be visible in the console. The output is available to a debugger via OutputDebugStringA.

Advanced: Other Ways to Control Logging

Overriding the Log File Path with an Environment Variable

You can force the browser to write its log file to a specific location by setting the CHROME_LOG_FILE environment variable.

• Example: export CHROME_LOG_FILE="chrome_debug.log" will write the log to the current working directory.

Overriding the Log File Path in Tests

To override the log file path in a C++ test, use this pattern:

#include "chrome/common/env_vars.h"
...
// Set the log file path in the environment for the test browser.
base::FilePath log_file_path = ...;
SetEnvironmentVariable(env_vars::kLogFileName, log_file_path.value().c_str());

How do I specify the command line flags?

See the command line flags page.

What personal information does the log file contain?

Before attaching chrome_debug.log to a bug report, be aware that it can contain some personal information, such as URLs opened during that session of Chrome.

Since the debug log is a human-readable text file, you can open it with a text editor and review the information it contains, and erase anything you do not want bug investigators to see.

The boilerplate values enclosed by brackets on each line are in the format: [process_id:thread_id:timestamp:log_level:file_name(line_number)]

Legacy Tools: Sawbuck (Windows)

Sawbuck is a tool for viewing log messages on Windows in a GUI. However, it is no longer actively maintained and may not work correctly with modern versions of Chrome, especially 64-bit builds (see crbug.com/456884).

If you still wish to use it, you can download it from the Sawbuck GitHub releases page.