/updatenow is an undocumented parameter, although it is defined in the executable.
Whether it actually performs any real function is unknown. Personally I've never seen any evidence that the /updatenow switch does what it's name implies, but it's possible that's because it's never been launched in the correct context.
I did get this log entry from the WindowsUpdate.log of a v7.6 WUA when running wuauclt /updatenow, which is more than I've ever seen with previous versions of the WUA.
2014-05-15 16:21:08:882 1088 2148 AU No installable updates are available
The only way I'm aware of to force the installation of detected patches is to launch the Windows Update applet (or launch an install from the Notification Area on WinXP/2003 systems).
Or use the Update Management tools in Patch Manager.
Even if it does have functionality, it's going to require that the installation files are already downloaded and ready for installation.
If that were the case here, we wouldn't be having this conversation. :-)
There are only three documented/functional parameters for use with the WUA:
- /detectnow
- /resetauthorization
- /reportnow
The official syntax is
wuauclt [[resetauthorization] detectnow] | [reportnow]