nginx - what is causing wordpress file empty error on uploads?

I can't seem to figure out why I get the following when I try to upload anything in wordpress... for both media uploads and wordpress import xml:

"Sorry, there has been an error.
File is empty. Please upload something more substantial. This error could also be >caused by uploads being disabled in your php.ini or by post_max_size being >defined as smaller than upload_max_filesize in php.ini."

Seems to be very little on how to troubleshoot this is online in way of nginx/php-fpm... most of which is about php.ini max configs or chmod, which... in my setup post_max_size is large enough as well as upload_max_filesize in /etc/php5/fpm/php.ini (as well as timeouts)... and chmod/chown seems correct for using separate php pools. Maybe someone can make heads or tails of this?

Here's my setup:

• Cloudflare (is off) to Floating IP


• Digitalocean Floating IP to droplet


• Droplet is Ubuntu 14.04 with nginx using php-fpm with pools created for each wordpress ms installation (x4 atm)



• SSL with Let's encrypt used for each wpms installation


• Chmod 755 for all wpms directories in site roots


• Chmod 644 for all wpms files in each site roots


• Chmod 660 for wp-config.php


• Chown each php5-fpm pool user on all files/directories for within their own site root
  eg: chown -R example1:example1 /home/example1/*


• Wordpress is one directory below their nginx conf roots. eg /home/example1/app/wordpress_files_here


• php.ini has uploads enabled with directory defined (/home/tmp/)

The users are NOT in www-data group nor sudo group,
I read doing so is a security risk but even so I temporarily tried adding them to www-data group to see if the wordpress uploading would work... it didn't.
I've also tried chown example1:www-data ownership as well, didn't work.
I've also tried chmod 777 for uploads folder, didn't work.

Error logs have the following:
in wpms-error.log (this also doesn't make sense to me)

2016/05/20 01:12:00 [crit] 1584#0: *1251 open() "/home/example1/example1.com-access.log" failed (13: Permission denied) while logging request, client: [my IP address], server: example1.com, request: "POST /wp-admin/admin-ajax.php HTTP/1.1", upstream: "fastcgi://unix:/var/run/php5-fpm-example1.sock", host: "example1.com", referrer: "https://example1.com/wp-admin/admin.php?import=wordpress&step=1&_wpnonce=dad4d82487"

in these site's nginx conf files I have:
access_log /home/example1/$host-access.log;

access logs are enabled in nginx.conf (even though not recommended) but access logs for each site is not being written to their site roots.

so... after trying everything I've read online... I've yet to find out even what the underlying issue is... because file permissions alone doesn't seem to be it? .. is it???

The following (after changing usernames to example1 etc) is ps aux | grep php results:

root       993  0.0  0.2 266688 11396 ?        Ss   May18   0:10 php-fpm: master process (/etc/php5/fpm/php-fpm.conf)
example1  1003  0.0  1.1 302568 45856 ?        S    May18   0:32 php-fpm: pool example1              
example1  1004  0.0  1.1 304620 47808 ?        S    May18   0:31 php-fpm: pool example1             
example2     1005  0.0  1.1 304360 47648 ?        S    May18   0:30 php-fpm: pool example2                   
example2     1007  0.0  1.1 302308 45956 ?        S    May18   0:30 php-fpm: pool example2                  
example3  1008  0.0  0.1 268640  7704 ?        S    May18   0:00 php-fpm: pool example3               
example3  1009  0.0  0.1 268640  7744 ?        S    May18   0:00 php-fpm: pool example3               
www-data  1010  0.0  0.1 266680  7560 ?        S    May18   0:00 php-fpm: pool www                     
www-data  1011  0.0  0.1 266680  7564 ?        S    May18   0:00 php-fpm: pool www                     
example4      1013  0.0  0.9 296016 39704 ?        S    May18   1:24 php-fpm: pool example4                   

example4      1014  0.0  1.3 310952 55024 ?        S    May18   1:23 php-fpm: pool example4                   
example5     1015  0.0  1.0 297352 40940 ?        S    May18   0:32 php-fpm: pool example5                  
example5     1016  0.0  1.1 305104 48232 ?        R    May18   0:32 php-fpm: pool example5                  
example4      1105  0.0  0.9 296016 39596 ?        S    May18   1:20 php-fpm: pool example4                    
example1  1313  0.0  0.9 296284 39884 ?        S    May18   0:31 php-fpm: pool example1              
example2     1317  0.0  1.1 304364 47628 ?        S    May18   0:29 php-fpm: pool example2                   
example5     1332  0.0  0.9 296880 39056 ?        S    May18   0:29 php-fpm: pool example5                   
example3  3727  0.0  0.0  11744   932 pts/1    S+   18:42   0:00 grep --color=auto php

example3 above is not a wpms site, it's just an empty root atm and that user is also in the sudo group and has it's own ssh login. I don't know if that's relevant.

Answer

This sounds like a permissions issue to me, likely around groups. I go into detail in this tutorial, but the gist is below

First the script I use to reset permissions

chown -R tim:www-data *
find /var/www/wordpress -type d -exec chmod 755 {} \;
find /var/www/wordpress -type f -exec chmod 644 {} \;
find /var/www/wordpress/wp-content/uploads -type f -exec chmod 664 {} \;

find /var/www/wordpress/wp-content/plugins -type f -exec chmod 664 {} \;
find /var/www/wordpress/wp-content/themes -type f -exec chmod 644 {} \;
chmod 440 /var/www/wordpress/wp-config.php
chmod -R g+s /var/www/wordpress/

Here are the main points from my tutorial - the information from that came from the wordpress.org website, mostly, I have references in my tutorial

• set owner to the user you created earlier, and group ownership to
  
  www-data


• Folder default is 755, standard


• File default is owner writable, readable by everyone


• Uploads folder writable by user and web server, so media can be uploaded by users


• Plugins folder writable by user and web server, so plugins can be added


• Themes folder only modifiable by owner