I have this problem: my /tmp in root is a separate partition and not very large. I have therefore changed the path in LyX (tools>settings) to a /tmp in my home and emptied the /tmp in root. That was apparently a bad idea, since now by trying to start lyx I get:
LyX could not create the temporary directory '/tmp/lyx_tmpdir63043uH0e4' Lyx is not starting anymore. Do I have to install LyX anew? Wolfgang
