How do I check Data Guard apply lag?

Query V$DATAGUARD_STATS and review the Apply Lag value.

How do I check Data Guard transport lag?

Query V$DATAGUARD_STATS and review the Transport Lag value.

How do I detect archive gaps?

Use SELECT * FROM V$ARCHIVE_GAP.

What is RMAN Backup Validation?

RMAN Backup Validation verifies Oracle backup integrity and recoverability without performing a restore.

What does RESTORE DATABASE VALIDATE do?

It verifies that RMAN backups can be restored successfully without actually restoring files.

How do I detect Oracle block corruption?

Use V$DATABASE_BLOCK_CORRUPTION and RMAN VALIDATE DATABASE CHECK LOGICAL.

What are the most important Oracle DBA interview topics?

Oracle Architecture, RMAN, Backup and Recovery, Data Guard, RAC, Performance Tuning, Security, and Troubleshooting are the most important Oracle DBA interview topics.

Is Oracle DBA still a good career in 2026?

Yes. Oracle DBA remains a strong career path due to the widespread use of Oracle databases in enterprise environments.

What Oracle version should I learn in 2026?

Oracle 19c and Oracle 23ai are the most valuable Oracle database versions to learn in 2026.

What does ORA-01034 ORACLE Not Available mean?

ORA-01034 indicates that the Oracle database instance is unavailable because it is not started, cannot be accessed, or failed during startup.

How do I fix ORA-01034?

Verify ORACLE_HOME and ORACLE_SID, review the Alert Log, check listener status, confirm background processes are running, and start the database using SQL*Plus as SYSDBA.

Why does ORA-27101 appear with ORA-01034?

ORA-27101 usually occurs when Oracle cannot locate the shared memory for the specified database instance because the database is not running or the environment variables are incorrect.

sqlplus: error while loading shared libraries: cannot restore segment prot after reloc: Permission denied

Applies to:

Oracle Enterprise Linux 5.5

Database 11gR1

Description:

I am using Oracle Enterprise Linux 5.5 and install Oracle Database 11gR1. After successfull installation of OS and Database when I try to login database it give me the following error:

sqlplus / as sysdba
sqlplus: error while loading shared libraries: /d01/app/oracle/product/11.2.0/dbhome_1/lib/libclntsh.so.11.1: cannot restore segment port after reloc: Permission denied

Solution:

Reason of the above error because of SELinux is running in ENFORCING mode, Oracle development has recommended the following workaround while they correct the problem. To check the mode execute the following command from root user:

root> getenforce
Enforcing

Switch SELinux from the default “Enforcing” mode that it is running in, to the “Permissive” mode.

root> setenforce 0

Now check again:

root> getenforce

Permissive

This allows SELinux to continue running, and logging denial messages, but SELinux will not actually deny any operations. Once Development has resolved this issue, you can (and should) return SELinux to the default “Enforcing” mode

Now successfully connect to SQL:

sqlplus / as sysdba

SQL*Plus: Release 11.2.0.1.0 Production on Tue Oct 30 11:56:08 2012

Connected to an idle instance.

SQL> startup;

ORACLE instance started.

Total System Global Area 4275781632 bytes

Fixed Size 2220200 bytes

Variable Size 1728057176 bytes

Database Buffers 2533359616 bytes

Redo Buffers 12144640 bytes

Database mounted.

Database opened.

SQL>

👉 Check our complete guide: Oracle Error Codes Guide

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About the Author

Rana Abdul Wahid is an experienced Oracle Database Administrator with expertise in Oracle Database Administration, Oracle Data Guard, RMAN Backup & Recovery, Oracle RAC, Oracle E-Business Suite, Performance Tuning, and High Availability Solutions.

Through this blog, he shares practical Oracle DBA solutions, troubleshooting guides, interview preparation resources, and production-tested best practices for database professionals worldwide.

5 comments:

AhmedFebruary 15, 2013 at 12:03:00 PM GMT+5
Thanks for sharing useful information. I've a question, does Oracle normally recommends to disable SELinux, I read it somewhere and did so on my server.
UnknownFebruary 15, 2013 at 10:55:00 PM GMT+5
Thanks for sharing.
UnknownFebruary 18, 2013 at 12:24:00 PM GMT+5
There are four shared libraries in the distribution , have to compile using Intel ICC compiler ,and those libraries perform relocation
so Oracle recommended SELINUX should be disable .
you can find these libraries by setting SELINUX to "permissive" which will log errors but allow actions SELINUX would otherwise deny.Now use audit2allow command or leave
leave SELINUX in "enforcing" mode use SELINUX troubleshooter to determine each error and troubleshooting report to fix.
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