The specified file 'temporary://file4b1kc1' could not be copied

 Got error ‘PHP message: Uncaught PHP Exception Drupal\Core\File\Exception\DirectoryNotReadyException: “The specified file ‘temporary://file4b1kc1’ could not be copied because the destination directory is not properly configured. This may be caused by a problem with file or directory permissions.” at /var/www/site/web/core/lib/Drupal/Core/File/FileSystem.php line 488\n’, referer: http://site.com/admin/config/development/backup_migrate

Or same from

referer: http://site.com/admin/reports/updates

https://www.drupal.org/forum/support/installing-drupal/2014-01-24/the-specified-file-temporaryfileh4oxvi-could-not-be

This is a file permissions issue.

From base of drupal site run

sudo chgrp -R www-data .

From site folder (e.g., sites/default) run

sudo chmod -R g+w files