nginx core dump backtrace

add strings to nginx.conf

worker_rlimit_core 500m;
working_directory /path/to/corefiles;

restart nginx.

Follow to /path/to/corefiles and wait for segfault :)

then gdb /path/to/nginx /path/to/core

inside gdb input bt

nginx basic auth (htpasswd)

Nginx supports basic auth (ngx_http_auth_basic_module)

directives:
auth_basic [|off]
auth_basic_user_file path/to/file

htpasswd file format:
# comment
login:password

Command htpasswd should be used with option -d , because nginx supports crypt() algorithm only.

Example:
htpasswd -c -d /etc/nginx/htpasswd asalnikov

nginx.conf part:
location /
{
auth_basic "closed site";
auth_basic_user_file /etc/nginx/htpasswd;
...
}

Nginx rewrite for user subdomains

For example you need to store few userpics for each user with possibility to set default userpic. First we must determine that for static content we will use nginx as one of the fastest web server. Userpics will be stored by scheme: "files/userpics/[first two letters from username]/[username]/"
directories scheme:

root@server:~# tree files
files
`-- userpics
|-- te
|   |-- test11
|   |   |-- 0.gif
|   |   |-- 1246347162.gif
|   |   |-- 1246362446.jpg
|   |   `-- 1246363739.gif
|   `-- test44
|       |-- 0.gif
|       |-- 1246365659.gif
|       `-- 1246366597.gif
`-- tu
   |-- turkish
   |   |-- 0.gif
   |   |-- 1246357650.gif
   |   |-- 1246357669.gif
   |   `-- 1246363992.gif
   `-- tuzik
       |-- 0.jpg
       |-- 1246365938.jpg
       `-- 1246365974.jpg

Default userpic will be addressed to 0.[jpg|png|gif] (file extension depends on extension the parent file)
Http request http://test11.mydomain.com/userpics/1246347162.gif must return this file:
/opt/www/files/userpics/te/test11/1246347162.gif
if file does not exist, nginx must return default userpic for this user:
/opt/www/files/userpics/te/test11/0.[jpg|png|gif]
if default userpic does not exist, nginx return default userpic for all users "/userpic-default.png"

part of nginx.conf:

location /userpics/ {
default_type image/jpeg;
root   /opt/www;
access_log /var/log/nginx/static.access.log  main;
if ($host ~* "(..)(.*)\.mydomain\.com") {
        set $a $1;
        set $b $2;
        rewrite ^/userpics/(.*)$ /files/userpics/$a/$a$b/$1;
}
if (!-f $request_filename) {
    rewrite ^/files/userpics/(.*)$ /files/userpics/$a/$a$b/0.jpg;
}
if (!-f $request_filename) {
    rewrite ^/files/userpics/(.*)$ /files/userpics/$a/$a$b/0.gif;
}
if (!-f $request_filename) {
    rewrite ^/files/userpics/(.*)$ /files/userpics/$a/$a$b/0.png;
}

break;
error_page   404 =200   /userpic-default.png;

}

UPD Best way: don't use "if" in location level.

try_files /files/userpics/$a/$a$b/0.jpg /files/userpics/$a/$a$b/0.gif /files/userpics/$a/$a$b/0.png /userpic-default.png;

regular expressions

Some tips about regular expressions:
(..) - two symbols
([0-9]{4}) - 4 numeric symbols
([a-c]+) - letters from a to c. many times as you like
(.*) - any symbols. many times as you like

A bit later I'll write about useful rewrite :)