One of our customer want to check their rman backup can be restore or not. As you know Oracle RMAN utility which you can try Verification whole backup, controlfile and so on.

While I am making this scenario I faced with below error message:

Starting restore at 19-AUG-20
using channel ORA_DISK_1
RMAN-00571: ================
RMAN-00569: ==== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ================
RMAN-03002: failure of restore command at 08/19/2020 23:13:41
RMAN-06026: some targets not found - aborting restore
RMAN-06025: no backup of archived log for thread 2 with sequence 26302 and starting SCN of 24674954085 found to restore
RMAN-06025: no backup of archived log for thread 2 with sequence 26301 and starting SCN of 24674835189 found to restore
RMAN-06025: no backup of archived log for thread 2 with sequence 26300 and starting SCN of 24674673364 found to restore
RMAN-06025: no backup of archived log for thread 2 with sequence 26299 and starting SCN of 24674438135 found to restore
RMAN-06025: no backup of archived log for thread 2 with sequence 26298 and starting SCN of 24674341864 found to restore
RMAN-06025: no backup of archived log for thread 2 with sequence 26297 and starting SCN of 24674135281 found to restore

Before start my db version is 11gR2 and I do not have RMAN catalog. So why this happen. Here is the explanations of this error:

The issue occurs when RMAN is not using catalog database and/or no catalog connection is made.  With a target only connection, the “ALL” keyword in the “RESTORE ARCHIVELOG ALL VALIDATE” statement does not take into account backup retention policy or archivelog files which are marked as deleted in the controlfile. 
Instead, it tries to access all archive log files referenced and will report RMAN-06025 for those of which it does not have a backup.   

When not using an RMAN catalog, use the below syntax from RMAN command prompt,for validating a subset of archivelog file backups.

RMAN> restore archivelog from time='<RECOVERY WINDOWS DAYS#>’ validate;

For example, suppose retention is set to ‘recovery window of 7 days’, then use the below command.

RMAN> show RETENTION POLICY;

RMAN configuration parameters are:

RMAN> CONFIGURE RETENTION POLICY TO RECOVERY WINDOW OF 3 DAYS;
RMAN> restore archivelog from time='SYSDATE-3' validate;

Reference:RMAN Command “RESTORE ARCHIVELOG ALL VALIDATE” Failing with RMAN-06025 (Doc ID 1391263.1)