Thanks for reporting the issue.

Waiting we transition to Qt5, I suggest that function "defaultTemporaryPath" is updated to use something like what is done here: https://github.com/commontk/CTK/blob/cdb75ce742f618112b8a0f299a484d00baa4e8ff/Applications/ctkPluginGenerator/ctkPluginGenerator.cpp#L45-L70

This is not a blocking issue, as a workaround is available:

• Go to menu: Edit / Application settings / Modules,
• Select a writeable directory as Temporary directory.

I think chances are it is definitely blocking for someone who just downloaded Slicer, and has no idea about what the problem or the workarounds are.

This issue is not new, and it has not prevented creating several stable versions. This is just one of many issues that users can solve without any software change, if they ask in the forum. Probably there are only very few Linux users, many of them do not have the issue or figure out the solution, because I don't see people complaining about it (even if only 1 out of 10 people reports the issue, we should see complaints coming in). Anyway, fix is scheduled for 4.8.

Submitted pull request with proposed fix:
https://github.com/Slicer/Slicer/pull/834

Fix integrated into r26549.

On unix-like systems, username is now appended to temporary directory name: (SystemTemporaryDir)/(ApplicationName)-(UserName)