With version 4.x most sensors will not show their serial number with any command.
The 4240 and 4255 being newer models do have a "show inventory" command in version 4.x that will show the serial number.
The IDSM-2 and NM-CIDS serial numbers should be viewable through the switch or router in which they are installed. Try the "show module" or "show inventory" commands on the switch or router.
For all other older appliance models (4210, 4215, 4235, 4250) you will need to physically look for the sticker on the box if you are running version 4.x.
In version 5.x the serial number of the sensor was added to the output of "show version". This functionality was added to all sensor models (all appliances and modules) as part of version 5.x.
I am assuming that you are looking for the serial numbers in order to get your contracts up to date and get the licenses for when you upgrade to version 5.0.
The easiest solution at this point is to just wait on getting the serial numbers until you've done the upgrade to 5.0. Then a simple "show version" will give you the serial number.
One concern you might have is that if you upgrade to 5.0 without having the serial number on hand then your sensors might stop working.
This is not the case. When you upgrade from 4.1 to 5.0 the sensor will convert the 4.1 config to 5.0 style config and will continue to work as normal even without a license.
All the license does is control the installation of signature updates on a version 5.0 sensor.
Without a license the signature update would be rejected by the sensor, but all other features on the sensor continue to work just fine.
The best thing to do is upgrade to 5.0 when you are ready, and use "show version" to get the serial number.
Then attempt to get a license for that serial number. If your service contracts are up to date then you should be able to get and apply the new license without a problem
BUT if you do have a problem getting the license, you do have another alternative. You can request a free 60 day Trial License (the Trial License would have to be requested for each sensor serial number).
This will give you an additional 60 days to get your contract up to date and get a full license (the only difference between the full and trial license is the time frame. The trial is only 60 days, the full license is for as long as your service contract).
Something to be aware of.
The service contracts that were purchased for version 4.x or earlier sensors are being converted to new version 5.x service contracts.
Most of these contracts have been converted, but there are still several that are in this conversion process.
Cisco is trying to get these converted as soon as possible, but it may still be a few weeks.
So if you can't get your sensors licensed this may be the issue.
In the meantime we have disabled the license checking in all of our updates. So the updates can be installed on the sensors with a license being required.
We won't be enforcing the license until after we have received word that all version 4.x service contracts have been converted to version 5.x contracts, and users have an opportunity to get their sensors licensed.
So if you upgrade to version 5.0 today, you can install the latest (and next few weeks worth) updates without any license. Once we start enforcing licenses then you can request the Trial License and get an additional 60 days of updates.
This hopefully will give you plenty of time to get the serial numbers, get your service contracts in order, and get your sensors licensed.
