If you get errors like this when upgrading LibreNMS to 1.40, see the article Resolving LibreNMS error "RuntimeException: The only supported ciphers are AES-128-CBC and AES-256-CBC with the correct key lengths" for a solution.
[root@beast42 /path/to/librenms]# tail -100 logs/librenms.log
[2018-06-04 18:16:17] production.ERROR: RuntimeException: The only supported ciphers are AES-128-CBC and AES-256-CBC with the correct key lengths. in /path/to/librenms/vendor/laravel/framework/src/Illuminate/Encryption/Encrypter.php:43
Stack trace:
#0 /path/to/librenms/vendor/laravel/framework/src/Illuminate/Encryption/EncryptionServiceProvider.php(27): Illuminate\Encryption\Encrypter->__construct('', 'AES-256-CBC')
#1 /path/to/librenms/vendor/laravel/framework/src/Illuminate/Container/Container.php(726): Illuminate\Encryption\EncryptionServiceProvider->Illuminate\Encryption\{closure}(Object(Illuminate\Foundation\Application), Array)
#2 /path/to/librenms/vendor/laravel/framework/src/Illuminate/Container/Container.php(608): Illuminate\Container\Container->build(Object(Closure))
#3 /path/to/librenms/vendor/laravel/framework/src/Illuminate/Container/Container.php(575): Illuminate\Container\Container->resolve('encrypter')
#4 /path/to/librenms/vendor/laravel/framework/src/Illuminate/Foundation/Application.php(728): Illuminate\Container\Container->make('encrypter')
#5 /path/to/librenms/vendor/laravel/framework/src/Illuminate/Container/Container.php(862): Illuminate\Foundation\Application->make('encrypter')
#6 /path/to/librenms/vendor/laravel/framework/src/Illuminate/Container/Container.php(790): Illuminate\Container\Container->resolveClass(Object(ReflectionParameter))
#7 /path/to/librenms/vendor/laravel/framework/src/Illuminate/Container/Container.php(757): Illuminate\Container\Container->resolveDependencies(Array)
#8 /path/to/librenms/vendor/laravel/framework/src/Illuminate/Container/Container.php(608): Illuminate\Container\Container->build('App\\Http\\Middle...')
#9 /path/to/librenms/vendor/laravel/framework/src/Illuminate/Container/Container.php(575): Illuminate\Container\Container->resolve('App\\Http\\Middle...')
#10 /path/to/librenms/vendor/laravel/framework/src/Illuminate/Foundation/Application.php(728): Illuminate\Container\Container->make('App\\Http\\Middle...')
#11 /path/to/librenms/vendor/laravel/framework/src/Illuminate/Pipeline/Pipeline.php(138): Illuminate\Foundation\Application->make('App\\Http\\Middle...')
#12 /path/to/librenms/vendor/laravel/framework/src/Illuminate/Routing/Pipeline.php(53): Illuminate\Pipeline\Pipeline->Illuminate\Pipeline\{closure}(Object(Illuminate\Http\Request))
#13 /path/to/librenms/vendor/laravel/framework/src/Illuminate/Pipeline/Pipeline.php(102): Illuminate\Routing\Pipeline->Illuminate\Routing\{closure}(Object(Illuminate\Http\Request))
#14 /path/to/librenms/vendor/laravel/framework/src/Illuminate/Routing/Router.php(574): Illuminate\Pipeline\Pipeline->then(Object(Closure))
#15 /path/to/librenms/vendor/laravel/framework/src/Illuminate/Routing/Router.php(533): Illuminate\Routing\Router->runRouteWithinStack(Object(Illuminate\Routing\Route), Object(Illuminate\Http\Request))
#16 /path/to/librenms/vendor/laravel/framework/src/Illuminate/Routing/Router.php(511): Illuminate\Routing\Router->dispatchToRoute(Object(Illuminate\Http\Request))
#17 /path/to/librenms/vendor/laravel/framework/src/Illuminate/Foundation/Http/Kernel.php(176): Illuminate\Routing\Router->dispatch(Object(Illuminate\Http\Request))
#18 /path/to/librenms/vendor/laravel/framework/src/Illuminate/Routing/Pipeline.php(30): Illuminate\Foundation\Http\Kernel->Illuminate\Foundation\Http\{closure}(Object(Illuminate\Http\Request))
#19 /path/to/librenms/vendor/laravel/framework/src/Illuminate/Foundation/Http/Middleware/TransformsRequest.php(30): Illuminate\Routing\Pipeline->Illuminate\Routing\{closure}(Object(Illuminate\Http\Request))
#20 /path/to/librenms/vendor/laravel/framework/src/Illuminate/Pipeline/Pipeline.php(148): Illuminate\Foundation\Http\Middleware\TransformsRequest->handle(Object(Illuminate\Http\Request), Object(Closure))
#21 /path/to/librenms/vendor/laravel/framework/src/Illuminate/Routing/Pipeline.php(53): Illuminate\Pipeline\Pipeline->Illuminate\Pipeline\{closure}(Object(Illuminate\Http\Request))
#22 /path/to/librenms/vendor/laravel/framework/src/Illuminate/Foundation/Http/Middleware/TransformsRequest.php(30): Illuminate\Routing\Pipeline->Illuminate\Routing\{closure}(Object(Illuminate\Http\Request))
#23 /path/to/librenms/vendor/laravel/framework/src/Illuminate/Pipeline/Pipeline.php(148): Illuminate\Foundation\Http\Middleware\TransformsRequest->handle(Object(Illuminate\Http\Request), Object(Closure))
#24 /path/to/librenms/vendor/laravel/framework/src/Illuminate/Routing/Pipeline.php(53): Illuminate\Pipeline\Pipeline->Illuminate\Pipeline\{closure}(Object(Illuminate\Http\Request))
#25 /path/to/librenms/vendor/laravel/framework/src/Illuminate/Foundation/Http/Middleware/ValidatePostSize.php(27): Illuminate\Routing\Pipeline->Illuminate\Routing\{closure}(Object(Illuminate\Http\Request))
#26 /path/to/librenms/vendor/laravel/framework/src/Illuminate/Pipeline/Pipeline.php(148): Illuminate\Foundation\Http\Middleware\ValidatePostSize->handle(Object(Illuminate\Http\Request), Object(Closure))
#27 /path/to/librenms/vendor/laravel/framework/src/Illuminate/Routing/Pipeline.php(53): Illuminate\Pipeline\Pipeline->Illuminate\Pipeline\{closure}(Object(Illuminate\Http\Request))
#28 /path/to/librenms/vendor/laravel/framework/src/Illuminate/Foundation/Http/Middleware/CheckForMaintenanceMode.php(46): Illuminate\Routing\Pipeline->Illuminate\Routing\{closure}(Object(Illuminate\Http\Request))
#29 /path/to/librenms/vendor/laravel/framework/src/Illuminate/Pipeline/Pipeline.php(148): Illuminate\Foundation\Http\Middleware\CheckForMaintenanceMode->handle(Object(Illuminate\Http\Request), Object(Closure))
#30 /path/to/librenms/vendor/laravel/framework/src/Illuminate/Routing/Pipeline.php(53): Illuminate\Pipeline\Pipeline->Illuminate\Pipeline\{closure}(Object(Illuminate\Http\Request))
#31 /path/to/librenms/vendor/laravel/framework/src/Illuminate/Pipeline/Pipeline.php(102): Illuminate\Routing\Pipeline->Illuminate\Routing\{closure}(Object(Illuminate\Http\Request))
#32 /path/to/librenms/vendor/laravel/framework/src/Illuminate/Foundation/Http/Kernel.php(151): Illuminate\Pipeline\Pipeline->then(Object(Closure))
#33 /path/to/librenms/vendor/laravel/framework/src/Illuminate/Foundation/Http/Kernel.php(116): Illuminate\Foundation\Http\Kernel->sendRequestThroughRouter(Object(Illuminate\Http\Request))
#34 /path/to/librenms/html/index.php(53): Illuminate\Foundation\Http\Kernel->handle(Object(Illuminate\Http\Request))
#35 {main}
[2018-06-04 18:16:17] production.ERROR: RuntimeException: The only supported ciphers are AES-128-CBC and AES-256-CBC with the correct key lengths. in /path/to/librenms/vendor/laravel/framework/src/Illuminate/Encryption/Encrypter.php:43
Stack trace:
#0 /path/to/librenms/vendor/laravel/framework/src/Illuminate/Encryption/EncryptionServiceProvider.php(27): Illuminate\Encryption\Encrypter->__construct('', 'AES-256-CBC')
#1 /path/to/librenms/vendor/laravel/framework/src/Illuminate/Container/Container.php(726): Illuminate\Encryption\EncryptionServiceProvider->Illuminate\Encryption\{closure}(Object(Illuminate\Foundation\Application), Array)
#2 /path/to/librenms/vendor/laravel/framework/src/Illuminate/Container/Container.php(608): Illuminate\Container\Container->build(Object(Closure))
#3 /path/to/librenms/vendor/laravel/framework/src/Illuminate/Container/Container.php(575): Illuminate\Container\Container->resolve('encrypter')
#4 /path/to/librenms/vendor/laravel/framework/src/Illuminate/Foundation/Application.php(728): Illuminate\Container\Container->make('encrypter')
#5 /path/to/librenms/vendor/laravel/framework/src/Illuminate/Container/Container.php(862): Illuminate\Foundation\Application->make('encrypter')
#6 /path/to/librenms/vendor/laravel/framework/src/Illuminate/Container/Container.php(790): Illuminate\Container\Container->resolveClass(Object(ReflectionParameter))
#7 /path/to/librenms/vendor/laravel/framework/src/Illuminate/Container/Container.php(757): Illuminate\Container\Container->resolveDependencies(Array)
#8 /path/to/librenms/vendor/laravel/framework/src/Illuminate/Container/Container.php(608): Illuminate\Container\Container->build('App\\Http\\Middle...')
#9 /path/to/librenms/vendor/laravel/framework/src/Illuminate/Container/Container.php(575): Illuminate\Container\Container->resolve('App\\Http\\Middle...')
#10 /path/to/librenms/vendor/laravel/framework/src/Illuminate/Foundation/Application.php(728): Illuminate\Container\Container->make('App\\Http\\Middle...')
#11 /path/to/librenms/vendor/laravel/framework/src/Illuminate/Foundation/Http/Kernel.php(215): Illuminate\Foundation\Application->make('App\\Http\\Middle...')
#12 /path/to/librenms/vendor/laravel/framework/src/Illuminate/Foundation/Http/Kernel.php(189): Illuminate\Foundation\Http\Kernel->terminateMiddleware(Object(Illuminate\Http\Request), Object(Illuminate\Http\Response))
#13 /path/to/librenms/html/index.php(58): Illuminate\Foundation\Http\Kernel->terminate(Object(Illuminate\Http\Request), Object(Illuminate\Http\Response))
#14 {main}