Intermittent authentication problems on SSH sessions

This document (7005754) is provided subject to the disclaimer at the end of this document.

Environment

SUSE Linux Enterprise Server 10 Service Pack 2
SUSE Linux Enterprise Server 10 Service Pack 3

Situation

A system, that has been upgraded from SUSE Linux Enterprise Server (SLES) 9 Service Pack (SP) 4 to SLES 10 SP 3, serves a high number of short term ssh connections from other clients (up to 10 authentication requests per second).
After the upgrade a small fraction of these (password based) authentication requests fail - even for users that have already been connected to the server with a message in the syslog like :

Invalid user <username> from <client-address>

All users are present in /etc/passwd, no LDAP or NIS involved.

This problem only occurs on less than one in thousand authentication requests.

Resolution

Disabling the name service cache daemon (nscd) and preventing it from being started during system boot resolves the issue.
This is done with the following commands :

# rcnscd stop
# chkconfig nscd off

Since the purpose of the name service cache daemon is to cache non-local user information, it is not needed in this setup and disabling it will not cause a performance degradation.

Disclaimer

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