please test update local/different server
turn on error reporting = development
all extentions/template up to date? (or post list/screenshot)
or set to different template
or https://forum.joomla.org/viewtopic.php?t=951496
or check for highlighted PHP settings: System → System Information → PHP Settings
or give more System information (as much as possible) php-version etc. https://docs.joomla.org/Help38:Site_System_Information
please report back when solved

@Mony25 Has your problem been resolved?

Set error reporting to development causes page to not display any content, no frontend nor backend, no joomla related error is shown.
System info:

Database Version | 5.5.55-0+deb7u1
Database Connection Collation | utf8mb4_general_ci
PHP Version | 5.6.30-1~dotdeb+7.1
Web Server | Apache/2.2.22 (Debian)
WebServer to PHP Interface | apache2handler

Extensions are up to date, change template didn't help, backend works fine but no frontend.
I can also send result of fpa script if you specify what values are important as result is quite long.

Thank you for testing.

Set error reporting to development causes page to not display any content, no frontend nor backend

Just to clarify:
Set error reporting to development while on 3.7.5 causes page to not display any content? (Please test "Fix database"-button)
Or set error reporting to development while on 3.7.5 shows no issues but after update to 3.8.0 it causes page to not display any content? (Please test your 3.7.5-backup+error reporting development+update on a different server)

to clarify: I set error reporting to development while on joomla 3.7.5 database is fine, I did fix database before setting error reporting. No content of backend or frontend is displayed (just "the site can't be reached" ) so I don't see any joomla errors, because of that.

@Mony25 We can try to resolve errors wile on 3.8.0 but if you have access to different server then restore 3.7.5 backup there and rerun the update as suggested by @CEWebDesign.

@wojsmol I don't have access to different server, so cannot try this option. I restored backup with version 3.7.5 to have working page for our copy writers.

@Mony25 Ok, then setup,a dev version from a 3.7.5 backup and run update there. Then in configuration.php set error reporting to at least maximum and report displayed errors.

updated 2 other sites all went fine, all is working

(this made me assume access to other servers...)
so these 2 other sites are on the same server/same php settings etc.
and we can exclude server based issues?

@wojsmol this is the one
Fatal error: Cannot redeclare class JModuleHelper in /var/www/sites2/testprelive.glocalities.com/plugins/system/t3/includes/joomla30/modulehelper.php on line 19

Based on this issue I assume to wait 'till fix for template will be available. T3 template issue

@CEWebDesign same server same settings for all sites, all of them also use same template T3_bs3_blank

From error we can see there is t3 system plugin issue.

Seeing this on one site. The upgrade did work on a Dev server.
What I see in the upgrade log is:
2017-09-26T11:46:37+00:00 INFO 204.187.34.100 update File Joomla_3.8.0-Stable-Update_Package.zip downloaded. 2017-09-26T11:46:37+00:00 INFO 204.187.34.100 update Starting installation of new version. 2017-09-26T11:47:23+00:00 INFO 204.187.34.100 update COM_JOOMLAUPDATE_UPDATE_LOG_FINALISE 2017-09-26T11:47:24+00:00 INFO 204.187.34.100 update COM_JOOMLAUPDATE_UPDATE_LOG_CLEANUP 2017-09-26T11:47:24+00:00 INFO 204.187.34.100 update COM_JOOMLAUPDATE_UPDATE_LOG_COMPLETE

When the upgrade works I am seeing:
2017-09-26T11:30:32+00:00 INFO 204.187.34.100 update File Joomla_3.8.0-Stable-Update_Package.zip downloaded. 2017-09-26T11:30:33+00:00 INFO 204.187.34.100 update Starting installation of new version. 2017-09-26T11:31:31+00:00 INFO 204.187.34.100 update Finalising installation. 2017-09-26T11:31:31+00:00 INFO 204.187.34.100 update Cleaning up after installation. 2017-09-26T11:31:31+00:00 INFO 204.187.34.100 update Update to version 3.8.0 is complete.

Not sure what the issue is, reverting to 3.7.5

Cheers.

@Mony25 Yes, please wait for the t3 template fix
@nsheehan Thank you for reporting. This is (just a minor) issue with the language strings. Please create a new issue for this issue, if you do not see error 500 on frontend and backend.

Seeing 500 errors on both front and back end. Front end just 500 error, backend blank admin area, menus shown but clicking anything also produces the 500 Application instantiation error, however it is only displayed in the page's tab.

Cheers

@nsheehan Thank you for info. Which template (and template-framework) is installed and are template+extentions up to date? Can you change template and set php to 7.0.x and test update please?

Using Yootheme, everything is up to date, no odd extensions. Troubleshooting included transferring the site to the dev server (identical IIS setups), restoring the database, testing that everything was working as expected and then we ran the Joomla update. There were some database errors at the end of the update, performing a database fix resolved those. The update log showed the expected entries on the dev server while the failed update logs are not quite as happy.

I'm testing moving the updated site to the live server now....

Can you post the failed update logs + database errors?

2017-09-26T11:46:37+00:00 INFO 204.187.34.100 update File Joomla_3.8.0-Stable-Update_Package.zip downloaded. 2017-09-26T11:46:37+00:00 INFO 204.187.34.100 update Starting installation of new version. 2017-09-26T11:47:23+00:00 INFO 204.187.34.100 update COM_JOOMLAUPDATE_UPDATE_LOG_FINALISE 2017-09-26T11:47:24+00:00 INFO 204.187.34.100 update COM_JOOMLAUPDATE_UPDATE_LOG_CLEANUP 2017-09-26T11:47:24+00:00 INFO 204.187.34.100 update COM_JOOMLAUPDATE_UPDATE_LOG_COMPLETE

Database error: ALTER TABLE #__fields_groups ADD COLUMN params TEXT NOT NULL AFTER ordering;

Appears to be the same as: https://issues.joomla.org/tracker/joomla-cms/17626

New postupdate problem on forum please.

@wojsmol isn't it better if i close most of the Update-Error-Threads?

New in forum, if any old get response please mention me :)

Set to "closed" on behalf of @franz-wohlkoenig by The JTracker Application at issues.joomla.org/joomla-cms/18064

closed as discussed above. This Issue can always reopened if necessary.

I reckon this issue is not resolved. I am getting the exact same error message front end and back end when updating from 3.7.5 to 3.8.1. Everything, extension and database, was up to date. Just googling around it seems to me that this is a much broader and general problem.

It may depend of your 3rd party extensions (plugins, templates).

I suggest to disable for a while

• all 3rd party plugins (specially from system group),
• disable core plugin "System - Remember Me"

Then try again to upgrade.

@swvanderlaan Please open new topic in https://forum.joomla.org/viewforum.php?f=710 if problem persist after @csthomas advice.