There might be several reasons for that, most of them revealing themselves by information in the startServer.log. But earlier today when trying to start the deployment manager it just would not start, saying that I had to look into the startServer.log, but even if I tried several times no new info was to be found. “ps -ef | grep java” revealed no WebSphere processes running, so still no clues. So I gave up and wanted to create a PMR, thus needing to zip the logs-folder, but that process failed. So then I ended up issuing a df-command, realizing that due to some previous heap dumps there was no more disk space left, which caused the dmgr not being able to start. Cleared the disk and voila, back on track.
Then later I got a problem when applications would not install, the error message was
WASX7114E: Cannot create temporary file in directory “null”
Found this technote http://www-01.ibm.com/support/docview.wss?uid=swg21300016 which mentions the same message, but the solution is simpler than in this case. In fact the /tmp-folder was full with dump-files as well. So when cleaned up, application installation worked as a charm again.