afivan

What I did was to switch from Apache to Nginx, started from scratch latest WP and put back the content, theme and plugins. For now it works, but the permissions are restricted so that WP cannot update itself or make any changes to its files. It works for ~5 days now, I really don’t know where the issue is/was, I think it’s something Apache or PHP related

I’ve activated the debug, you can see the error now

So if I do this in my wordpress folder:
mkdir wp-includes2
cp wp-includes/* -r wp-includes2/
rm wp-includes/* -r
cp wp-includes2/* -r wp-includes

It works again, but I expect it to crash again in 1-2 days. It means the wordpress installation is not broken, but there’s something wrong somewhere else, that’s why I suspect a bug in Apache or PHP.

Yes I did that. I ran these commands in /var/www directory. In ~/wordpress I’ve extracted the clean WP

cp wordpress/ wordpress2 -r
cp ~/wordpress/* wordpress -r
cp wordpress2/wp-config.php wordpress
~/fix-wp-permissions.sh /var/www/wordpress

My fix-wp-permissions.sh looks like this:
#!/bin/bash
#
# This script configures WordPress file permissions based on recommendations
# from http://codex.ww.wp.xz.cn/Hardening_WordPress#File_permissions
#
# Author: Michael Conigliaro <mike [at] conigliaro [dot] org>
#
WP_OWNER=www-data # <– wordpress owner
WP_GROUP=www-data # <– wordpress group
WP_ROOT=$1 # <– wordpress root directory
WS_GROUP=www-data # <– webserver group

# reset to safe defaults
find ${WP_ROOT} -exec chown ${WP_OWNER}:${WP_GROUP} {} \;
find ${WP_ROOT} -type d -exec chmod 755 {} \;
find ${WP_ROOT} -type f -exec chmod 644 {} \;

# allow wordpress to manage wp-config.php (but prevent world access)
chgrp ${WS_GROUP} ${WP_ROOT}/wp-config.php
chmod 660 ${WP_ROOT}/wp-config.php

# allow wordpress to manage wp-content
find ${WP_ROOT}/wp-content -exec chgrp ${WS_GROUP} {} \;
find ${WP_ROOT}/wp-content -type d -exec chmod 775 {} \;
find ${WP_ROOT}/wp-content -type f -exec chmod 664 {} \;