Updated Linux Mint as below post in anticipation of installing Java. Which because of a recent serious Java issue I’m a little leery about. Why do this? Because I read about Z390 Portable Mainframe Assembler and Emulator and it sounds interesting. This PDF says “A test program named ZOPCHECK was developed to verify all 2357 opcode, mnemonic, and operand combination. They have a github which saw activity 16 days ago, as of this post. I also found this interesting because it says z390 is written in J2SE compatible Java and is distributed under a GNU open source license. So perhaps Oracle Java isn’t required. There are many other interesting thing mentioned such as a VSAM, CICS, COBOL and a DFSORT compatible sort. There is a user group here.