Error in writing to directory /tmp Please ensure that this directory is writable and has atleast 60 MB of disk space. Installation cannot continue.

I recently got an increasing flood of the same error in all the server environments:

Error in writing to directory /tmp/OraInstallYYYY-MM-DD_HH-MM-SSAM Please ensure that this directory is writable and has atleast 60 MB of disk space. Installation cannot continue.

Tmp has always got 0777, always plenty of space, Oracle Installer creates a folder in Tmp, but fails writing. Some sources online suggest Temp2 type solution of creating another temporary folder, pass TMP and TEMP variables to the shell, but not all shells and environments accept those.

I have no cure, but based on recent testing it all boils down to this checklist:
- place installer in Oracle home directory (or complete equivalent)
- unpack zips, cpios with Oracle user you are going to use for installation
- run installer from an installation directory with Oracle user (not using full path)
- check if unzip is installed

At least last couple of times first step solved the problem. It looks like Oracle user fails writing somewhere, but it reports it with dummy error.