Zimbra backup broken after upgrade to Ubuntu 16.04 LTS
After upgrading from Zimbra ZCS 7.8.0 on Ubuntu 14.04 LTS to Zimbra ZCS 7.8.1 on Ubuntu 16.04 LTS, backups where suddenly not working any longer. Instead of the usual “SUCCESS” e-mail, I would get two e-mails about a failure, both essentially containing the error message “Error occurred: system failure: LDAP backup failed: system failure: exception during auth {RemoteManager: myzimbrahost.example.com->zimbra@myzimbrahost.example.com:22}”.
As it turns out, this was caused by an SSH authentication problem. Zimbra was still using an old DSA key for SSH, which is not supported in Ubuntu 16.04 LTS any longer (at least it is deactivated by default). The fix is simple: After running zmsshkeygen and zmupdateauthekys (both must be run as the zimbra user), Zimbra uses an RSA key-pair and authentication works again.