Start Ray with Custom Temp Dir

Oct 13, 2025 by wbrum.org 144 views

What happened + What you expected to happen

When using ray start with the --temp-dir option to specify a custom temporary directory, the get_user_temp_dir() function in ray._private.utils fails to honor this user-specified directory. This is a critical issue that affects the functionality of Ray, as it prevents users from customizing the temporary directory for their Ray sessions.

Expected Behavior

The get_user_temp_dir() function should return the user-specified temporary directory when ray start is used with the --temp-dir option. This would allow users to control the location of temporary files generated by Ray, which is essential for managing disk space and ensuring data integrity.

Versions / Dependencies

This issue is specific to the Nightly version of Ray. It is essential to note that this issue may not be present in the stable version of Ray.

Reproduction Script

To reproduce this issue, follow these steps:

Start Ray with Custom Temp Dir: Run the following command to start Ray with a custom temporary directory:

ray start --head --temp-dir=/tmp/my-temp-dir

   This command starts Ray in head mode and specifies the custom temporary directory `/tmp/my-temp-dir`.

2. **Verify get_user_temp_dir()**: Run the following Python code to verify that `get_user_temp_dir()` returns the correct temporary directory:
   ```python
import ray
print(ray._private.utils.get_user_temp_dir())

This code imports the ray module and prints the result of get_user_temp_dir(). However, instead of returning the custom temporary directory /tmp/my-temp-dir, it returns the default temporary directory tmp.

Issue Severity

The severity of this issue is Low. While it may cause frustration for users who rely on custom temporary directories, it does not prevent the execution of Ray or cause any critical errors.

Solution

To fix this issue, the get_user_temp_dir() function needs to be modified to honor the user-specified temporary directory. This can be achieved by checking the --temp-dir option passed to ray start and returning the custom temporary directory if it is specified.

Modified get_user_temp_dir() Function

Here is an example of how the get_user_temp_dir() function can be modified to honor the user-specified temporary directory:

import argparse

def get_user_temp_dir():
    parser = argparse.ArgumentParser()
    parser.add_argument('--temp-dir', help='Custom temporary directory')
    args = parser.parse_args()
    if args.temp_dir:
        return args.temp_dir
    else:
        return '/tmp'

This modified function uses the argparse module to parse the --temp-dir option passed to ray start. If the option is specified, it returns the custom temporary directory; otherwise, it returns the default temporary directory /tmp.

Conclusion

Q&A: Frequently Asked Questions

Q: What is the purpose of the `get_user_temp_dir()` function in Ray?

A: The get_user_temp_dir() function is used to retrieve the temporary directory for Ray. It is essential for managing disk space and ensuring data integrity.

Q: Why doesn't the `get_user_temp_dir()` function honor the user-specified temporary directory?

A: The get_user_temp_dir() function fails to honor the user-specified temporary directory because it does not check the --temp-dir option passed to ray start. As a result, it returns the default temporary directory instead of the custom directory specified by the user.

Q: How can I reproduce this issue?

A: To reproduce this issue, follow these steps:

Start Ray with a custom temporary directory using the --temp-dir option: ray start --head --temp-dir=/tmp/my-temp-dir
Run the following Python code to verify that get_user_temp_dir() returns the correct temporary directory:

import ray print(ray._private.utils.get_user_temp_dir())

   This code imports the `ray` module and prints the result of `get_user_temp_dir()`. However, instead of returning the custom temporary directory `/tmp/my-temp-dir`, it returns the default temporary directory `tmp`.

#### Q: What is the severity of this issue?

A: The severity of this issue is **Low**. While it may cause frustration for users who rely on custom temporary directories, it does not prevent the execution of Ray or cause any critical errors.

#### Q: How can I fix this issue?

A: To fix this issue, the `get_user_temp_dir()` function needs to be modified to honor the user-specified temporary directory. This can be achieved by checking the `--temp-dir` option passed to `ray start` and returning the custom temporary directory if it is specified.

#### Q: What is the modified `get_user_temp_dir()` function?

A: Here is an example of how the `get_user_temp_dir()` function can be modified to honor the user-specified temporary directory:
```python
import argparse

def get_user_temp_dir():
    parser = argparse.ArgumentParser()
    parser.add_argument('--temp-dir', help='Custom temporary directory')
    args = parser.parse_args()
    if args.temp_dir:
        return args.temp_dir
    else:
        return '/tmp'

Q: Why is it essential to honor the user-specified temporary directory?

A: Honoring the user-specified temporary directory is essential for managing disk space and ensuring data integrity. By allowing users to customize the temporary directory, Ray can prevent data loss and ensure that temporary files are stored in a location that is easily accessible and manageable.

Q: Can I use a different temporary directory for different Ray sessions?

A: Yes, you can use a different temporary directory for different Ray sessions by specifying the --temp-dir option when starting Ray. For example:

ray start --head --temp-dir=/tmp/session1

This command starts Ray in head mode and specifies the custom temporary directory /tmp/session1 for the current session.

Q: How can I report this issue to the Ray developers?

A: If you encounter this issue, you can report it to the Ray developers by creating a new issue on the Ray GitHub repository. Please provide a detailed description of the issue, including the steps to reproduce it, and any relevant code or logs.