Casper has this built into inventory, you can look up any machine and it should tell you want software updates are available, otherwise from the terminal you can do this:

bash-3.2# softwareupdate -l Software Update Tool Copyright 2002-2007 Apple

Software Update found the following new or updated software: RemoteDesktopAdmin34-3.4 Remote Desktop Admin Update (3.4), 57930K [recommended] Safari5.0.5Leopard-5.0.5 Safari (5.0.5), 48209K [recommended] [restart] AirPortUtility-5.5.2 AirPort Utility (5.5.2), 11990K [recommended] QuickTime-7.6.9 QuickTime (7.6.9), 70195K [recommended] [restart] JavaForMacOSX10.5Update9-1.0 Java for Mac OS X 10.5 Update 9 (1.0), 122901K [recommended] SecUpd2011-002-1.0 Security Update 2011-002 (1.0), 249666K [recommended] [restart] * iTunesX-10.2.2 iTunes (10.2.2), 75674K [recommended] bash-3.2#

That does not seem to work for me for some reason. It complains that it is not able to talk to "swscan.apple.com" possibly b/c of a proxy issue although SoftwareUpdate -l just works fine. Has anyone else seen this?
Adil

We also get this because we're behind a proxy. It seems that if you do a jamf recon it runs into the problem but if a recon is run via policy then it seems to work ok. Not sure why a machine would need to go out to Apple if it's using a local SUS. JAMF support confirmed that the jamf binary is not proxy aware so that may be the root issue.

j
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Jared F. Nichols
Desktop Engineer, Client Services
Information Services Department
MIT Lincoln Laboratory
244 Wood Street
Lexington, Massachusetts 02420
781.981.5436