(1) Download zcs-8.0.8 – do not use zimbra 8.0.5 because it causes problems
(2) Backup the /opt/zimbra/ directory somewhere after shutting down zimbra
(3) Unpack the zcs-8.0.8 somewhere and then install ./install.sh –platform-override
(4) When upgrading – you have to install memcache and zimbra proxy – these two things are required by 8.8 – so if these are not installed we cannot upgrade to 8.8
(5) After zimbra 8.0.8 is installed and that you have tested things to work then we can proceed to upgrade to 8.8
(6) Make sure that ldap accepts untrusted certs otherwise a lot of problems to follow; run the following:-

su - zimbra
zmlocalconfig -e ssl_allow_untrusted_certs=true
zmlocalconfig -e ldap_starttls_supported=0
zmlocalconfig -e ldap_starttls_required=false
zmlocalconfig -e ldap_common_require_tls=0
zmcontrol restart

the above is important because somehow there will be ldap problems with the upgrade.

Recently (as of around November 2021) the Zimbra repo stopped working properly and some important packages have become unavailable. If you run into upgrade problems from 8.0.8 to 8.8.15 like:-

** During the upgrade process if you get errors such as:-
zimbra-ldap-components is missing. ERROR

Then need to check install logs to see what the problem is:-
perl-Socket6-0.23-4.el6.x86_64.rpm is needed on centos 6 so that needs to be downloaded and installed

if there is a problem with domain names not being resolvable-
zmprov md domain.com -zimbraVirtualHostname webmail.domain.com

e.g. there are problems starting nginx saying that the domains are not recognised then you can try to remove them:-

Actually zimbra should be running at the point of upgrading to 8.8 because ldap needs to be online.

(7) Unpack zcs-8.8 and then perform the install ./install.sh

You might want to run the upgrade using the command “screen” as the upgrade process can take around 20-30 minutes….

If you run into problems then the following resources might help.

Failed upgrades:-
https://wiki.zimbra.com/wiki/Recovering_from_upgrade_failure

Basically, you need to check the reason for the failure – in our case it could be because the rpms did not install. The install file is here:-
/tmp/install.log.XXXXXX <= this is different for each install attempt If the problem can be fixed then we could run the command to redo the installation/upgrade ./install.sh --force-upgrade --skip-activation-check --skip-upgrade-check error: Failed dependencies: zimbra-mbox-war >= 8.8.15.1568694943-1.r6 is needed by zimbra-mbox-service-8.8.15.1568694943-1.r6.x86_64
zimbra-mbox-admin-console-war is needed by zimbra-store-8.8.15_GA_3869.RHEL6_64-20190917004220.x86_64
zimbra-mbox-store-libs is needed by zimbra-store-8.8.15_GA_3869.RHEL6_64-20190917004220.x86_64
zimbra-mbox-webclient-war is needed by zimbra-store-8.8.15_GA_3869.RHEL6_64-20190917004220.x86_64
zimbra-mbox-war is needed by zimbra-store-8.8.15_GA_3869.RHEL6_64-20190917004220.x86_64

Other potential issues are with yum, and you can clear the cache for yum by running these commands:-

yum clean all
yum clean metadata
yum clean dbcache
yum makecache