DOCUMENTATION: When and how to clear the NetBackup host cache

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NetBackup 7.0.1 introduces the caching of host name to IP address mappings, which minimizes the delays encountered during repeated lookups for an name or address that cannot be resolved. Each NetBackup process has an in-memory cache and all NetBackup processes on the same host also share a on-disk cache.


Each cache entry has a life span of one hour, for both successful and unsuccessful resolution attempts, to suppress the otherwise repeated lookups. Accordingly, NetBackup may not recognize changes to the hosts file or DNS immediately.

NetBackup 7.1 retains the same one hour default life span for cache entries.  However, if the host_cache on-disk is manually cleared, the in-memory caches will be discarded after 10 seconds.


Manual : NetBackup 7.0 Commands, Page 77

Modification Type:  Addition


bpclntcmd -clear_host_cache

For NetBackup 7.0.1 and above, this option will remove all the entries in the NetBackup on-disk host cache that resides on the file system.  Cleared entries are recreated the next time a NetBackup process, that does not have an associated entry within the in-memory cache, attempts to resolve the hostname or IP address.


Clearing the cache on the file system does not immediately affect the in-memory cache of each currently running NetBackup process.  

For NetBackup 7.0.1, the in-memory cache entries are refreshed only when their life span is exceeded.  To force an immediate update of the in-memory cache, stop and restart the process or processes.  

For NetBackup 7.1, clearing the on-disk cache will result in an update to the in-memory cache after 10 seconds.


Clearing the cache on one host does not affect hostname or IP address resolution on other hosts, so it may be necessary clear the on-disk cache and restart processes on multiple hosts if it is not possible to wait an hour for the life span of an outdated entry to expire on all the hosts.


Basic Troubleshooting:

If a stale host cache entry is believed to be causing a NetBackup problem, the bpclntcmd can be used to display the cached IP address associated with the hostname or cached hostname associated with the IP address. 


bpclntcmd -hn <hostname> 

bpclntcmd -ip <ip_address>   

If the returned value differs from those shown by operating system tools – such as ping and traceroute and tracert - the local host cache should be cleared.   To recreate the cache entry, simply display the name/IP mapping again using either bpclntcmd or the Host Properties within the administrative console.

NetBackup 7.6 will also display stale cache entries in the bptestnetconn output.


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