default wordpress limit is 2m. But this is not a wordpress limit.
Changed on debian:
$ cat /etc/php5/cgi/php.ini | grep post_max
post_max_size = 8M
In the server context:
$ cat /etc/nginx/sites-enabled/default | grep max
client_max_body_size 8M;
restart:
# sh /etc/init.d/php5-cgi restart
# /usr/sbin/nginx -s reload
materials used:
http://www.cyberciti.biz/faq/linux-unix-bsd-nginx-413-request-entity-too-large/
http://wiki.nginx.org/HttpCoreModule#client_max_body_size