Is Informix 11 DB Unix needs to be re-installed as Informix 11 DB for Linux?

Thanks in advance.

Not sure what you call "unix". It's probably some version of AIX, HP-UX, Solaris or something similar, which runs on different hardware.

As any other software, Informix binaries must match the OS and architecture you're using. So at least the software installation must be done on Linux.

Porting the datafiles is not supported. You should export/import the database. But it could work... theoretically... if the architecture is similar (32/64bits and same endianess)
Regards

As Mr F.N. says, if you install Informix on another server, you need to install the binaries adapted to the target machine, because you need at least you need to be licensed for this new installation, even for Innovator-C Edition.

As per data files, don't play with fire, run a dbexport/dbimport to migrate your databases.

If you are above 11.50 xC5, this is also an excellent opportunity to play around with the external tables instead of dbimport :-)
You will how faster this technique is.

Best regards
E.