Script Description:
This Linux shell script runs from the PRIMARY DB server to monitor and checks the lag/synchronization status between Primary and Standby Oracle DBs and reports the lag [if happened] to the user.

Download the script:
https://www.dropbox.com/s/a9k3rn928vj3ooc/check_standby_lag.sh?dl=0

How to use the script:
Unfortunately, this script will not work unless you manually modify the variables’ values in brown color to match your environment: [Those variables are at the begging of the script]

# Here you replace youremail@yourcompany.com with your Email address:
EMAIL_RECEIVER=”youremail@yourcompany.com“
export EMAIL_RECEIVER

# Replace ${ORACLE_SID} with the Primary DB instance SID:
ORACLE_SID=${ORACLE_SID}
export ORACLE_SID

# Replace STANDBY_TNS_ENTRY with the Standby Instance TNS entry you configured in the primary site tnsnames.ora file: e.g. orcl_standby
DRDBNAME=STANDBY_TNS_ENTRY
export DRDBNAME

# Replace ${ORACLE_HOME} with the ORACLE_HOME path on the primary server:
ORACLE_HOME=${ORACLE_HOME}
export ORACLE_HOME

# Log Directory Location:
LOG_DIR=’/tmp’
export LOG_DIR

# Here you replace SYSPASS with user SYS password on the standby DB: [The worst part I know :-)]
CRD=’SYSPASS‘
export CRD

# Replace “5” with the number of LAGGED ARCHIVELOGS if reached an Email alert will be sent to the receiver:
LAGTHRESHOLD=5
export LAGTHRESHOLD

You can schedule this script in the crontab to run e.g. every 15 minutes to get you alerted if the number of lagged archive logs cross the predefined threshold.

Reminder: This script runs from the primary DB server NOT from the standby server.
Hope you will find it useful.

This script is part of DBA Bundle scripts: http://dba-tips.blogspot.ae/2014/02/oracle-database-administration-scripts.html