I enabled captcha with "Number of unsuccessful attempts to login=0" for admin sign in then cleared all the caches, but after I logged out then tried to log in admin page, Captcha is invisible, so I always got error message "incorrect form key". I tried cleared browser cache as well, did not help.
from the log file, the problem seems to be related to "main.CRITICAL: Cannot change permissions for path "/var/www/html/magento2/pub/media/captcha/admin" Warning!chmod(): Operation not permitted"
Is this a known bug?
BTW I checked one more thing. I can see entry in /etc/passwd for apache user but I cannot su to it, also there is no /home/apache directory. I exactly followed the magento2 installation procedure step by step, not sure whether this is normal.
Thanks in advance!