Thread:Project:Support desk/upload tmp dir - MediaWiki ignores php specified path/reply

Set the TMP (or TEMP or TMPDIR) environment variables for what you want your temp directory. (for the upload by url error)

For the install error, this can be caused if php is configured to store session files in the temp directory (sesssion.save_path in your php.ini). This should cause logins to not work at all, but perhaps only mediawiki is dissallowed, and php session handlers don't have the open_basedir restriction. If you get that warning when installing, but can still log in after the install is done, then the warning is in error, and is a bug in the installer (should probably file a bug about it).