1. I think you modify the configure file to install mbstring in the first place
2. Not unless you clear the configure files when doing a complete apache/php upgrade following the instructions located here:
http://help.directadmin.com/item.php?id=26
Otherwise I think it should be fine.
3. I have no idea on this since I am not on the DA Staff, but my guts tell me no since its not really a base system necessity. (for the most part)
I haven't tried installing mbstring but you can give this a try if you feel up to it. Just to help you get started hopefully since I gathered this from the php.net website.
Modify the file /usr/local/directadmin/customapache/configure.php
and add the following to the end of the file
And maybe the following as well, not sure
Code:
--enable-mbstr-enc-trans
--enable-mbregex
See
http://us3.php.net/mbstring under the installation section.
After you've done that try running
./build php in the /usr/local/directadmin/customapache directory.
[font color=red]
Be sure to backup your original configure.php file and php.ini just in case. [/font]
If that seemed successful verify the variables available in the php.ini file to configure mbstring. (See the php.net/mbstring under Runtime Configuration)
After you've done all that try restarting apache or your server and see if it all works. If not better restore your php.ini file and recompile php without mbstring and start to debug.d