alert log stop writing suddenly...

alert log stopped writing since around 2 hrs...please help..

FS has plenty of space.

Filesystem GB blocks Free %Used Iused %Iused Mounted on/dev/picore_diag 34.00 33.84 1% 501 1% /opt/oracle/diag/rdbms/picore

size of alert log is also small..

/opt/oracle/diag/rdbms/picore/PICORE/trace> ls -ltr|grep alert

-rw-r----- 1 oracle dba 150683 Sep 27 10:39 alert_PICORE.log_bkp

-rwxr-x--- 1 oracle dba 0 Sep 27 14:04 alert_PICORE.log

took a backup of alert log and created a new one....still not writing....

here are the last few lines:

Fri Sep 27 10:39:13 2013Shutting down instance (immediate)Stopping background process SMCOShutting down instance: further logons disabledStopping background process MMNLStopping background process MMONLicense high water mark = 2ALTER DATABASE CLOSE NORMALFri Sep 27 10:39:18 2013SMON: disabling tx recoverySMON: disabling cache recoveryFri Sep 27 10:39:18 2013Shutting down archive processesArchiving is disabledArchive process shutdown avoided: 0 activeThread 1 closed at log sequence 7Successful close of redo thread 1Completed: ALTER DATABASE CLOSE NORMALALTER DATABASE DISMOUNTShutting down archive processesArchiving is disabledCompleted: ALTER DATABASE DISMOUNTARCH: Archival disabled due to shutdown: 1089Shutting down archive processesArchiving is disabledFri Sep 27 10:39:18 2013Stopping background process VKTMARCH: Archival disabled due