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example
Or for longer, use three backticks above and below the code snippet:
longer
example
here
Some or all of the below information will be requested if it isn’t supplied; for fastest response please provide as much as you can 
Nextcloud version (eg, 12.0.2): Nextcloud 15.0.4
Operating system and version (eg, Ubuntu 17.04): debian strech
Apache or nginx version (eg, Apache 2.4.25): nginx version: nginx/1.10.3
PHP version (eg, 7.1): PHP 7.0.33-0+deb9u1
The issue you are facing:
Is this the first time you’ve seen this error? (Y/N): Y
Steps to replicate it:
In Admin > external storage I’m obtain this error:
Internal server error
The server is unable to execute your request.
If this happens again, please send the technical details below to the server administrator.
The server log file can provide more information.
Technical information
Remote address: Ip gateway
Request ID: yUAHUBTgwlZsmuIxtCBr
The output of your Nextcloud log in Admin > Logging:
[index] Error: Exception: HMAC does not match. at <<closure>>
0. /var/www/nextcloud/lib/private/Security/CredentialsManager.php line 92
decrypt("*** sensitive parameters replaced ***")
1. /var/www/nextcloud/apps/files_external/lib/Lib/Auth/Password/GlobalAuth.php line 55
retrieve("", "password::global")
2. /var/www/nextcloud/apps/files_external/lib/Settings/Admin.php line 71
getAuth("")
3. /var/www/nextcloud/settings/Controller/CommonSettingsTrait.php line 115
getForm()
4. /var/www/nextcloud/settings/Controller/AdminSettingsController.php line 74
formatSettings({40: [OCA\Files_ ... ]})
5. /var/www/nextcloud/settings/Controller/CommonSettingsTrait.php line 126
getSettings("externalstorages")
6. /var/www/nextcloud/settings/Controller/AdminSettingsController.php line 65
getIndexResponse("admin", "externalstorages")
7. /var/www/nextcloud/lib/private/AppFramework/Http/Dispatcher.php line 166
index("externalstorages")
8. /var/www/nextcloud/lib/private/AppFramework/Http/Dispatcher.php line 99
executeController(OC\Settings\Cont ... {}, "index")
9. /var/www/nextcloud/lib/private/AppFramework/App.php line 118
dispatch(OC\Settings\Cont ... {}, "index")
10. /var/www/nextcloud/lib/private/AppFramework/Routing/RouteActionHandler.php line 47
main("OC\\Settings\\C ... r", "index", OC\AppFramework\ ... {}, {section: "exter ... "})
11. <<closure>>
__invoke({section: "exter ... "})
12. /var/www/nextcloud/lib/private/Route/Router.php line 297
call_user_func(OC\AppFramework\ ... {}, {section: "exter ... "})
13. /var/www/nextcloud/lib/base.php line 987
match("/settings/admin/externalstorages")
14. /var/www/nextcloud/index.php line 42
handleRequest()
GET /index.php/settings/admin/externalstorages
from 192.168.1.254 by christophe at 2019-02-21T13:29:02+00:00
The output of your config.php file in /path/to/nextcloud (make sure you remove any identifiable information!):
cat /var/www/nextcloud/config/config.php
<?php
$CONFIG = array (
'passwordsalt' => 'SALT',
'secret' => 'password',
'trusted_domains' =>
array (
0 => 'localhost',
1 => 'tld.tld.fr',
),
'datadirectory' => '/media/data/cloud',
'overwrite.cli.url' => 'http://localhost',
'dbtype' => 'mysql',
'version' => '15.0.4.0',
'dbname' => 'nextcloud',
'dbhost' => 'localhost',
'dbport' => '',
'dbtableprefix' => 'oc_',
'dbuser' => 'nextcloud',
'dbpassword' => 'password',
'installed' => true,
'instanceid' => 'IDinstance',
'ldapIgnoreNamingRules' => false,
'ldapProviderFactory' => '\\OCA\\User_LDAP\\LDAPProviderFactory',
'updatechecker' => false,
'memcache.local' => '\\OC\\Memcache\\APCu',
'integrity.check.disabled' => true,
'filelocking.enabled' => true,
'memcache.locking' => '\\OC\\Memcache\\Redis',
'redis' =>
array (
'host' => 'localhost',
'port' => '6379',
'timeout' => '0.0',
'password' => '',
),
'logout_url' => 'https://tld.tld.fr/yunohost/sso/?action=logout',
'theme' => '',
'loglevel' => 2,
'maintenance' => false,
'mail_smtpmode' => 'sendmail',
'mail_from_address' => 'christophe',
'mail_domain' => 'tld.fr',
);
The output of your Apache/nginx/system log in /var/log/____:
192.168.1.254 - - [21/Feb/2019:15:36:34 +0100] "GET /index.php/settings/admin/externalstorages HTTP/2.0" 500 11447 "-" "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/72.0.3626.81 Safari/537.36"
192.168.1.254 - - [21/Feb/2019:15:36:34 +0100] "POST /index.php/apps/ojsxc/http-bind HTTP/2.0" 200 911 "-" "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/72.0.3626.81 Safari/537.36"
192.168.1.254 - - [21/Feb/2019:15:36:35 +0100] "GET /core/fonts/Nunito-Bold.woff2 HTTP/2.0" 302 782 "https://tld.tld.fr/core/css/guest.css?v=71e96c6d-0" "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/72.0.3626.81 Safari/537.36"
192.168.1.254 - - [21/Feb/2019:15:36:35 +0100] "GET /core/fonts/Nunito-Regular.woff2 HTTP/2.0" 302 779 "https://tld.tld.fr/core/css/guest.css?v=71e96c6d-0" "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/72.0.3626.81 Safari/537.36"
192.168.1.254 - - [21/Feb/2019:15:36:35 +0100] "GET /index.php/apps/ojsxc/js/config HTTP/2.0" 200 1004 "-" "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/72.0.3626.81 Safari/537.36"
192.168.1.254 - - [21/Feb/2019:15:36:35 +0100] "GET /index.php/settings/admin/undefined/img/notifications.svg HTTP/2.0" 302 782 "-" "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/72.0.3626.81 Safari/537.36"
192.168.1.254 - - [21/Feb/2019:15:36:35 +0100] "GET /ocs/v2.php/apps/notifications/api/v2/notifications HTTP/2.0" 200 627 "-" "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/72.0.3626.81 Safari/537.36"
192.168.1.254 - - [21/Feb/2019:15:36:35 +0100] "GET /index.php/apps/files/ HTTP/2.0" 200 67176 "-" "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/72.0.3626.81 Safari/537.36"
192.168.1.254 - - [21/Feb/2019:15:36:36 +0100] "GET /index.php/apps/files/ HTTP/2.0" 200 67179 "-" "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/72.0.3626.81 Safari/537.36"
192.168.1.254 - - [21/Feb/2019:15:36:36 +0100] "GET /index.php/apps/files/ HTTP/2.0" 200 67176 "-" "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/72.0.3626.81 Safari/5
in database, this table “oc_external_mounts” have not one rows.
Have you got idea for this error?
I want share one foleder for all users this my server an on user have authorized for deposit more file this.
thank’s for your help.