encountered the same problem in Informix on Redhat linux:
15:22:27 Event alarms enabled. ALARMPROG = '/opt/informix/etc/log_full.sh'
15:22:27 Booting Language <c> from module <>
15:22:27 Loading Module <CNULL>
15:22:27 Booting Language <builtin> from module <>
15:22:27 Loading Module <BUILTINNULL>
15:22:32 Informix Dynamic Server 2000 Version 9.21.UC4 Software Serial Number ACN#J334914
15:22:33 Informix Dynamic Server 2000 Initialized -- Shared Memory Initialized.
15:22:33 Physical Recovery Started at Page(1:580).
15:22:33 Physical Recovery Complete: 0 Pages Examined 0 Pages Restored.
15:22:33 Logical Recovery Started.
15:22:33 10 recovery worker threads will be started.
15:22:36 Logical Recovery Complete.
0 Committed, 0 Rolled Back, 0 Open, 0 Bad Locks
15:22:37 Dataskip is now OFF for all dbspaces
15:22:37 On-Line Mode
15:22:37 Checkpoint Completed: duration was 0 seconds.
15:22:37 Checkpoint loguniq 6, logpos 0x213018
16:28:06 Fuzzy Checkpoint Completed: duration was 0 seconds, 38 buffers not flushed.
16:28:06 Checkpoint loguniq 6, logpos 0x26216c
16:33:06 Fuzzy Checkpoint Completed: duration was 0 seconds, 38 buffers not flushed.
16:33:06 Checkpoint loguniq 6, logpos 0x26316c
16:55:58 listener-thread: err = -951: oserr = 0: errstr = informix2000: Incorrect password or user informix2000 is not known on the database server.
17:18:08 Fuzzy Checkpoint Completed: duration was 2 seconds, 38 buffers not flushed.
17:18:08 Checkpoint loguniq 6, logpos 0x2c916c
17:19:19 Logical Log Files are Full -- Backup is Needed