update package to 2.3.5?

https://launchpad.net/ubuntu/+ppas

Just because something is newer doesn't get it in the main repos. Packages are tested as good so that new users get a solid experience of Ubuntu. If there is sufficient reason to update it (bug fixes / security fixes it will be included. The link above may help you find a PPA of someone whom has packaged the later version for you to download.

You can request that it be updated in n-series, by submitting a bug report. Please make sure to read https://help.ubuntu.com/community/ReportingBugs carefully first.

Sorry, I mean p-series. (n-series was Natty. ;-) )

what is the p-series exactly?

p-series refers to future release 12.04 LTS. I don't think its codename has been selected yet. (Terms like p-series are used officially on launchpad as milestone names, see https://launchpad.net/ubuntu/p-series.) While Oneiric is not yet out, it is close enough to release that it is very unlikely for a new upstream version of gkrellm to be included, as per https://wiki.ubuntu.com/FeatureFreeze and https://wiki.ubuntu.com/FreezeExceptionProcess.

p-series (12.04) is not derived from another series.

So no wonder :)

It seems that such derivation information may be recent metadata. Lucid, Maverick, and Natty are also indicated not to derive from any other series. Oneiric is indicated to derive from Sid (which is the permanent codename for Debian's unstable series, from which all releases of Ubuntu derive). I presume that this metadatum will be updated for p-series at some point.

Alternatively, perhaps older series are indicated to no longer derive from Sid when Sid gets new enough that the package versions don't match up. I'm not sure.