INFORMIX-SQL 4.1 - There's this ASCII UNIX file called "passwd" in /usr/informix/etc which
holds all the user id's and encrypted passwords to log into ISQL.
Is there a system catalog table which holds the logged in users?
I see a SYSUSERS.DAT file but when I queried it, it didnt show my login id, date or time.
First of all, INFORMIX-SQL 4.10 was released in 1989 or 1990; you have a seriously ancient product there (not as ancient as ISQL 2.10.06, though--not quite). Since you have a file 'SYSUSERS.DAT' in upper-case, you must be running on a DOS or Windows machine - the Unix platforms would have the name in lower case. Your database engine is Informix Standard Engine (rather than Informix OnLine or Informix Dynamic Server).
The file /usr/informix/etc/passwd is not a standard, Informix-provided file. It is some add-on created by someone.
Given the commentary below, it appears that the DOS or Windows versions of ISQL did provide some password management tools - something I was not aware of. It was never propagated to the Unix line of the code.
The sysusers system catalog table records who is allowed to connect to the database - and who is the DBA, and so on. It does not record who is connected; in fact, with Informix Standard Engine, there is no record of who is currently connected anywhere in the DBMS or DB.
The columns in the sysusers table are user name (with 'public' as a special pseudo-username meaning 'anybody') plus their status (C connect, D DBA, R resource), and a priority - I don't know that there's much meaning to that, though the person who creates the database gets a priority of 9 - and in some versions a password which has no documented use.
Frank asks:
What was the last version of ISQL for MS-DOS, 4.1?
I don't keep as good a record of when software was and was not available for MS-DOS or MS Windows variants. There is a moderate chance that there was a version 5.x servers for these platforms, which would mean that the corresponding ISQL was 4.1x. I doubt if there was ever a version of ISQL for MS-DOS with the 6.x or later servers; by that time, it would have been for Windows rather than just MS-DOS.
Was NEW-ERA = I4GL for MS-DOS, or was there another I4GL version for DOS?
No. NewEra was a replacement for I4GL that ran on Windows (not DOS). There was a separate I4GL for DOS - it would have been released at the same time as ISQL for DOS. NewEra is dead; very dead. I seem to remember there being an I4GL for Windows (separate from NewEra), but that has not been produced for many (15+) years either.
Are any of these versions still around (available)?
No. I would estimate that Informix stopped supporting MS-DOS (as opposed to Windows) about 15 years ago (±3 years, probably). The material is unlikely to be available in even archival form. As already stated in answers to other questions - this stuff is simply not available any more. As in, the original supplier no longer has the material to ship. As far as Informix is concerned, there are no machines using MS-DOS any more; there are only Windows machines.
I don't have an answer to the password issue, but I would like to say that I wrote a program many years ago using ISQL for MS-DOS 4.1 and I an still using it TODAY. I have ALL the user manuals and have ALL the software for Informix 4.1 for DOS.