Magento2: Cron script readiness check failed. Found non-writable path(s): [magento_dir]/bin/magento [magento_dir]/setup/html

[JoshuaFlood]

When attempting to perform a readiness check via the system update utility in the backend, I receive the following error:

Check Cron Scripts
Cron script readiness check failed.
Error from Updater Application Cron Script:
Found non-writable path(s):
[magento_dir]/bin/magento
[magento_dir]/setup/html

I have attempted to properly set permissions again, to no avail.

I can see in var/log/update.log that the filepaths to both of these directories contain whitespace, both at the beginning of the filepath and following the [magento_dir] directory, before the trailing forward slash. I'm not sure if this is the source of the issue, or something to do with the formatting of log files.

I have confirmed, though, that the symlink at [magento_dir]/setup/html is broken.
When I issue the command ls [magento_dir]/setup/html, then I recieve the following error ls: cannot access 'setup/html': Too many levels of symbolic links.

Preconditions

1. Magento 2.2.3 installed via composer using Redis for all cache storage, running in Developer mode.
2. Ubuntu 16.04
3. Apache 2.4
4. MySQL 5.7.22
5. PHP 7.1
6. Varnish Cache with nginx for SSL termination running on a separate server.
7. Permissions set for a post-installation developer environment as per magento documentation.
8. Ownership has been assigned to the www-data group in order to retain proper permissions on upgrade/deployment etc.
9. Magento user has been added to the www-data group.

Steps to reproduce

1. Access Magento System Upgrade utility via admin panel.
2. Perform readiness check.

Expected result

1. Readiness check successful.

Actual result

1. Received 'Cron script readiness check failed' error during 'Check Cron Scripts' test.

[JoshuaFlood]

Following the steps described in this issue, the error for the path [magento_dir]/bin/magento has disappeared, however the error for path [magento_dir]/setup/html still occurs.

[anthr76]

I'm having this same issue

[JoshuaFlood]

It seems incredibly common and caused by all kinds of different things, from what I've read, though I haven't found any reports of exactly the same error message. Are you having problems with the setup/html symlink as well?

I have added this issue as a question to the magento stackexchange. My question contains links to solutions for other errors with the Cron readiness check, but not this one. Hopefully at least one of us can get it working!

[JoshuaFlood]

The issue is also mentioned here, albeit with errors about different paths.

[ghost]

@JoshuaFlood , thank you for your report.
We were not able to reproduce this issue by following the steps you provided. If you'd like to update it, please reopen the issue.