Answers.Body: <blockquote>
    <p>This answer was contributed after troubleshooting in comments on the original question.</p>
  </blockquote>
  
  <p>This error can appear for a variety of reasons, but most commonly when Craft believes it isn't installed.</p>
  
  <p>The installation process begins at <code>/admin/install</code>, but is dependent upon the <a href="https://docs.craftcms.com/v3/config/config-settings.html#cptrigger" rel="nofollow noreferrer"><code>cpTrigger</code></a> config value. That this page wasn't accessible (or, more specifically, produced the same error instead the Admin or installation wizard) led the asker to conclude that the config value had been updated by the prior developer.</p>
  
  <p>Craft may believe it isn't installed if it can't find the expected tables—sometimes complicated by using a <a href="https://docs.craftcms.com/v3/config/db-settings.html#tableprefix" rel="nofollow noreferrer"><code>tablePrefix</code> setting</a>, in the database configuration. This setting exists in the event you need to maintain more than one Craft install side-by-side, in the same database.</p>
  
  <p>In this case, a combination of these two settings made it difficult to tell why Craft was producing the <code>503</code> error.</p>
  
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2019-12-06T00:27:17.387Z
Answers.LastActivityDate: 2019-12-06T00:27:17.387Z
Answers.UserDisplayName: August Miller
Answers.Body: <p>Try accessing the CP-Panel, in most cases this error occurs due to config files not being set correctly, thus not allowing craft to connect to the DB.</p>
  
  <p>If you get the installer page when accessing the CP-Pannel, that means it's most likely not able to access the DB with your current configs.</p>
  
  <p>Usually the URL would be my-host.com/backstage
  however this may differ based on your <code>cpTrigger</code> config value in <code>config/general.php</code>.</p>
  
  <p>Edit: <code>devMode</code> should be set to <code>true</code> in <code>config/general.php</code>.</p>
  
  <p>If this doesn't resolve the issue, try clearing your entire logs folder, calling your page and then uploading those log files as a zip file to any file hoster so we can take closer look at it, your current output from your web.log doesn't show too much... </p>
  
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2019-12-05T19:07:23.840Z
Answers.Text: `admin` is the default `cpTrigger` value—might be worth updating, granted most installs will be configured as such, out of the box. Otherwise, great recommendations, thorough answer! 
Answers.UserDisplayName: August Miller
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2019-12-05T21:33:08.840Z
Answers.Text: This was another stumbling block. The cpTrigger had been set to a different value so I was getting the same error when trying to access the default /admin.
Answers.UserDisplayName: Tyssen
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2019-12-05T14:25:18.453Z
Answers.LastActivityDate: 2019-12-05T14:25:18.453Z
Answers.UserDisplayName: Campiotti
Body: <p>I've cloned a Craft 3 repo that was created by another developer and I'm trying to get it running on my local server but I get</p>
  
  <blockquote>
    <p>HTTP 503 – Service Unavailable – craft\web\ServiceUnavailableHttpException</p>
  </blockquote>
  
  <p>I've created a quick db test script to test my database connection…</p>
  
  <pre><code>&lt;?php
  $dbname = 'local';
  $dbuser = 'root';
  $dbpass = 'root';
  $dbhost = 'localhost';
  
  $link = mysqli_connect($dbhost, $dbuser, $dbpass) or die("Unable to Connect to '$dbhost'");
  mysqli_select_db($link, $dbname) or die("Could not open the db '$dbname'");
  
  $test_query = "SHOW TABLES FROM $dbname";
  $result = mysqli_query($link, $test_query);
  
  $tblCnt = 0;
  while($tbl = mysqli_fetch_array($result)) {
    $tblCnt++;
    #echo $tbl[0]."&lt;br /&gt;\n";
  }
  
  if (!$tblCnt) {
    echo "There are no tables&lt;br /&gt;\n";
  } else {
    echo "There are $tblCnt tables&lt;br /&gt;\n";
  }
  ?&gt;
  </code></pre>
  
  <p>which works fine. The settings for the db are the same as in my <code>.env</code> file…</p>
  
  <pre><code># Craft general settings
  ENVIRONMENT="dev"
  SECURITY_KEY="ftwC-@gdkN3H7XakRd8ekYQ.n6BrNq_t3DaoZZnY"
  
  # Craft database settings
  DB_DRIVER="mysql"
  DB_SERVER="localhost"
  DB_USER="root"
  DB_PASSWORD="root"
  DB_DATABASE="local"
  DB_SCHEMA="public"
  DB_TABLE_PREFIX=""
  DB_PORT="4095"
  </code></pre>
  
  <p>I've checked the permissions of files and folders as described in the installation docs. </p>
  
  <p>What else should I be looking for?</p>
  
  <p>EDIT: As suggested, I've looked in <code>storage/logs/web.log</code> and this is what I get:</p>
  
  <pre><code>    2019-12-05 08:35:08 [-][-][d97bb3d28a3fdd84f8c8edc795e22e6d][info][yii\db\Connection::open] Opening DB connection: mysql:host=localhost;dbname=local;port=4095;
      2019-12-05 08:35:08 [-][-][d97bb3d28a3fdd84f8c8edc795e22e6d][profile begin][yii\db\Connection::open] Opening DB connection: mysql:host=localhost;dbname=local;port=4095;
      2019-12-05 08:35:08 [-][-][d97bb3d28a3fdd84f8c8edc795e22e6d][profile end][yii\db\Connection::open] Opening DB connection: mysql:host=localhost;dbname=local;port=4095;
      2019-12-05 08:35:08 [-][-][d97bb3d28a3fdd84f8c8edc795e22e6d][info][yii\db\Command::query] SHOW TABLES
      2019-12-05 08:35:08 [-][-][d97bb3d28a3fdd84f8c8edc795e22e6d][profile begin][yii\db\Command::query] SHOW TABLES
      2019-12-05 08:35:08 [-][-][d97bb3d28a3fdd84f8c8edc795e22e6d][profile end][yii\db\Command::query] SHOW TABLES
      2019-12-05 08:35:09 [-][-][d97bb3d28a3fdd84f8c8edc795e22e6d][trace][yii\base\Module::getModule] Loading module: exifReturn
      2019-12-05 08:35:09 [-][-][d97bb3d28a3fdd84f8c8edc795e22e6d][trace][yii\base\Application::bootstrap] Bootstrap with modules\exifreturn\ExifReturn
      2019-12-05 08:35:09 [-][-][d97bb3d28a3fdd84f8c8edc795e22e6d][info][yii\web\Session::open] Session started
      2019-12-05 08:35:09 [-][-][d97bb3d28a3fdd84f8c8edc795e22e6d][error][yii\web\HttpException:503] craft\web\ServiceUnavailableHttpException in /app/pb-repo/vendor/craftcms/cms/src/web/Application.php:529
      Stack trace:
      #0 /app/pb-repo/vendor/craftcms/cms/src/web/Application.php(187): craft\web\Application-&gt;_processInstallRequest(Object(craft\web\Request))
      #1 /app/pb-repo/vendor/yiisoft/yii2/base/Application.php(386): craft\web\Application-&gt;handleRequest(Object(craft\web\Request))
      #2 /app/pb-repo/web/index.php(21): yii\base\Application-&gt;run()
      #3 {main}
      2019-12-05 08:35:09 [-][-][d97bb3d28a3fdd84f8c8edc795e22e6d][trace][yii\base\View::renderFile] Rendering view file: /app/pb-repo/vendor/yiisoft/yii2/views/errorHandler/exception.php
      2019-12-05 08:35:09 [-][-][d97bb3d28a3fdd84f8c8edc795e22e6d][trace][yii\base\View::renderFile] Rendering view file: /app/pb-repo/vendor/yiisoft/yii2/views/errorHandler/callStackItem.php
      2019-12-05 08:35:09 [-][-][d97bb3d28a3fdd84f8c8edc795e22e6d][trace][yii\base\View::renderFile] Rendering view file: /app/pb-repo/vendor/yiisoft/yii2/views/errorHandler/callStackItem.php
      2019-12-05 08:35:09 [-][-][d97bb3d28a3fdd84f8c8edc795e22e6d][trace][yii\base\View::renderFile] Rendering view file: /app/pb-repo/vendor/yiisoft/yii2/views/errorHandler/callStackItem.php
      2019-12-05 08:35:09 [-][-][d97bb3d28a3fdd84f8c8edc795e22e6d][trace][yii\base\View::renderFile] Rendering view file: /app/pb-repo/vendor/yiisoft/yii2/views/errorHandler/callStackItem.php
      2019-12-05 08:35:08 [-][-][d97bb3d28a3fdd84f8c8edc795e22e6d][info][application] $_GET = []
  
      $_POST = []
  
      $_FILES = []
  
      $_COOKIE = [
          'CraftSessionId' =&gt; 'd97bb3d28a3fdd84f8c8edc795e22e6d'
      ]
  
      $_SESSION = [
          'bd62416aa8538ede709019a5e113eea5__flash' =&gt; []
      ]
  
      $_SERVER = [
          'USER' =&gt; 'www-data'
          'HOME' =&gt; '/var/www'
          'SCRIPT_NAME' =&gt; '/index.php'
          'REQUEST_URI' =&gt; '/'
          'QUERY_STRING' =&gt; ''
          'REQUEST_METHOD' =&gt; 'GET'
          'SERVER_PROTOCOL' =&gt; 'HTTP/1.0'
          'GATEWAY_INTERFACE' =&gt; 'CGI/1.1'
          'REMOTE_PORT' =&gt; '50902'
          'SCRIPT_FILENAME' =&gt; '//app/pb-repo/web/index.php'
          'SERVER_ADMIN' =&gt; 'webmaster@localhost'
          'CONTEXT_DOCUMENT_ROOT' =&gt; '/app/pb-repo/web'
          'CONTEXT_PREFIX' =&gt; ''
          'REQUEST_SCHEME' =&gt; 'http'
          'DOCUMENT_ROOT' =&gt; '/app/pb-repo/web'
          'REMOTE_ADDR' =&gt; '172.17.0.1'
          'SERVER_PORT' =&gt; '80'
          'SERVER_ADDR' =&gt; '172.17.0.5'
          'SERVER_NAME' =&gt; 'pb.local'
          'SERVER_SOFTWARE' =&gt; 'Apache/2.4.10 (Debian)'
          'SERVER_SIGNATURE' =&gt; ''
          'PATH' =&gt; '/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin'
          'HTTP_COOKIE' =&gt; 'CraftSessionId=d97bb3d28a3fdd84f8c8edc795e22e6d'
          'HTTP_UPGRADE_INSECURE_REQUESTS' =&gt; '1'
          'HTTP_ACCEPT_ENCODING' =&gt; 'gzip, deflate, br'
          'HTTP_ACCEPT_LANGUAGE' =&gt; 'en-GB,en;q=0.5'
          'HTTP_ACCEPT' =&gt; 'text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8'
          'HTTP_USER_AGENT' =&gt; 'Mozilla/5.0 (Macintosh; Intel Mac OS X 10.13; rv:70.0) Gecko/20100101 Firefox/70.0'
          'HTTP_CONNECTION' =&gt; 'close'
          'HTTP_X_FORWARDED_PROTO' =&gt; 'https'
          'HTTP_X_FORWARDED_HOST' =&gt; 'pb.local'
          'HTTP_X_FORWARDED_FOR' =&gt; '192.168.95.1'
          'HTTP_X_REAL_IP' =&gt; '192.168.95.1'
          'HTTP_HOST' =&gt; 'pb.local'
          'proxy-nokeepalive' =&gt; '1'
          'HTTPS' =&gt; 'on'
          'FCGI_ROLE' =&gt; 'RESPONDER'
          'PHP_SELF' =&gt; '/index.php'
          'REQUEST_TIME_FLOAT' =&gt; 1575534907.7596
          'REQUEST_TIME' =&gt; 1575534907
          'ALLOW_UPDATES' =&gt; '1'
          'ALLOW_ADMIN_CHANGES' =&gt; '1'
          'BACKUP_ON_UPDATE' =&gt; '0'
          'DEV_MODE' =&gt; '1'
          'ENABLE_TEMPLATE_CACHING' =&gt; '1'
          'ENVIRONMENT' =&gt; 'dev'
          'IS_SYSTEM_LIVE' =&gt; '1'
          'RUN_QUEUE_AUTOMATICALLY' =&gt; '1'
          'SECURITY_KEY' =&gt; '••••••••••••••••••••••••••••••••••••••••'
          'SITE_NAME' =&gt; ''
          'DB_DRIVER' =&gt; 'mysql'
          'DB_SERVER' =&gt; 'localhost'
          'DB_USER' =&gt; 'root'
          'DB_PASSWORD' =&gt; '••••'
          'DB_DATABASE' =&gt; 'local'
          'DB_SCHEMA' =&gt; 'public'
          'DB_TABLE_PREFIX' =&gt; ''
          'DB_PORT' =&gt; '4095'
          'ASSETS_URL' =&gt; ''
          'UPLOADS_URL' =&gt; '/uploads/'
          'SITE_URL' =&gt; 'https://pb.local/'
          'WEB_ROOT_PATH' =&gt; '.'
          'PUBLIC_PATH' =&gt; './web/'
          'DEFAULT_SITE_URL' =&gt; 'https://pb.local'
      ]
  </code></pre>
  
  <p>So it seems to be connecting OK, showing tables, loading some modules, starting the session, and then returning the httpException error. </p>
  
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2019-12-05T04:46:56.463Z
Comments.Text: I'd recommend [turning on `devMode`](https://docs.craftcms.com/v3/config/config-settings.html#devmode) for the development environment to get more information about the error, and checking `storage/logs/web.log` for a stack trace.
Comments.UserDisplayName: August Miller
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2019-12-05T08:42:37.427Z
Comments.Text: I've added the most recent output from `web.log`.
Comments.UserDisplayName: Tyssen
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2019-12-05T19:09:46.950Z
Comments.Text: Also worth looking at your table names to ensure it's not [using a `tablePrefix`](https://docs.craftcms.com/v3/config/db-settings.html) (if your tables all begin with something like `craft_`, then you may need to include this in your database config / `.env`.
Comments.UserDisplayName: August Miller
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2019-12-05T21:32:23.050Z
Comments.Text: That was it! There was a table prefix but I hadn't bothered to look closely at the tables after I imported the database.
Comments.UserDisplayName: Tyssen
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2022-03-16T00:35:19.100Z
Comments.Text: I had a similar problem, and found that my database user was not set up with proper permissions. I found this in the logs, very helpful.
Comments.UserDisplayName: 4midori
Tags: <craft3><error-message>
Title: HTTP 503 – Service Unavailable error
ThreadText: # HTTP 503 – Service Unavailable error
  
  (Asked by: username_0 on 2019-12-04)
  
  I've cloned a Craft 3 repo that was created by another developer and I'm trying to get it running on my local server but I get
  
  > HTTP 503 – Service Unavailable – craft\web\ServiceUnavailableHttpException
  
  I've created a quick db test script to test my database connection…
  
  ```
  <?php
  $dbname = 'local';
  $dbuser = 'root';
  $dbpass = 'root';
  $dbhost = 'localhost';
  
  $link = mysqli_connect($dbhost, $dbuser, $dbpass) or die("Unable to Connect to '$dbhost'");
  mysqli_select_db($link, $dbname) or die("Could not open the db '$dbname'");
  
  $test_query = "SHOW TABLES FROM $dbname";
  $result = mysqli_query($link, $test_query);
  
  $tblCnt = 0;
  while($tbl = mysqli_fetch_array($result)) {
    $tblCnt++;
    #echo $tbl[0]."<br />\n";
  }
  
  if (!$tblCnt) {
    echo "There are no tables<br />\n";
  } else {
    echo "There are $tblCnt tables<br />\n";
  }
  ?>
  
  ```
  
  which works fine. The settings for the db are the same as in my `.env` file…
  
  ```
  # Craft general settings
  ENVIRONMENT="dev"
  SECURITY_KEY="ftwC-@gdkN3H7XakRd8ekYQ.n6BrNq_t3DaoZZnY"
  
  # Craft database settings
  DB_DRIVER="mysql"
  DB_SERVER="localhost"
  DB_USER="root"
  DB_PASSWORD="root"
  DB_DATABASE="local"
  DB_SCHEMA="public"
  DB_TABLE_PREFIX=""
  DB_PORT="4095"
  
  ```
  
  I've checked the permissions of files and folders as described in the installation docs.
  
  What else should I be looking for?
  
  EDIT: As suggested, I've looked in `storage/logs/web.log` and this is what I get:
  
  ```
      2019-12-05 08:35:08 [-][-][d97bb3d28a3fdd84f8c8edc795e22e6d][info][yii\db\Connection::open] Opening DB connection: mysql:host=localhost;dbname=local;port=4095;
      2019-12-05 08:35:08 [-][-][d97bb3d28a3fdd84f8c8edc795e22e6d][profile begin][yii\db\Connection::open] Opening DB connection: mysql:host=localhost;dbname=local;port=4095;
      2019-12-05 08:35:08 [-][-][d97bb3d28a3fdd84f8c8edc795e22e6d][profile end][yii\db\Connection::open] Opening DB connection: mysql:host=localhost;dbname=local;port=4095;
      2019-12-05 08:35:08 [-][-][d97bb3d28a3fdd84f8c8edc795e22e6d][info][yii\db\Command::query] SHOW TABLES
      2019-12-05 08:35:08 [-][-][d97bb3d28a3fdd84f8c8edc795e22e6d][profile begin][yii\db\Command::query] SHOW TABLES
      2019-12-05 08:35:08 [-][-][d97bb3d28a3fdd84f8c8edc795e22e6d][profile end][yii\db\Command::query] SHOW TABLES
      2019-12-05 08:35:09 [-][-][d97bb3d28a3fdd84f8c8edc795e22e6d][trace][yii\base\Module::getModule] Loading module: exifReturn
      2019-12-05 08:35:09 [-][-][d97bb3d28a3fdd84f8c8edc795e22e6d][trace][yii\base\Application::bootstrap] Bootstrap with modules\exifreturn\ExifReturn
      2019-12-05 08:35:09 [-][-][d97bb3d28a3fdd84f8c8edc795e22e6d][info][yii\web\Session::open] Session started
      2019-12-05 08:35:09 [-][-][d97bb3d28a3fdd84f8c8edc795e22e6d][error][yii\web\HttpException:503] craft\web\ServiceUnavailableHttpException in /app/pb-repo/vendor/craftcms/cms/src/web/Application.php:529
      Stack trace:
      #0 /app/pb-repo/vendor/craftcms/cms/src/web/Application.php(187): craft\web\Application->_processInstallRequest(Object(craft\web\Request))
      #1 /app/pb-repo/vendor/yiisoft/yii2/base/Application.php(386): craft\web\Application->handleRequest(Object(craft\web\Request))
      #2 /app/pb-repo/web/index.php(21): yii\base\Application->run()
      #3 {main}
      2019-12-05 08:35:09 [-][-][d97bb3d28a3fdd84f8c8edc795e22e6d][trace][yii\base\View::renderFile] Rendering view file: /app/pb-repo/vendor/yiisoft/yii2/views/errorHandler/exception.php
      2019-12-05 08:35:09 [-][-][d97bb3d28a3fdd84f8c8edc795e22e6d][trace][yii\base\View::renderFile] Rendering view file: /app/pb-repo/vendor/yiisoft/yii2/views/errorHandler/callStackItem.php
      2019-12-05 08:35:09 [-][-][d97bb3d28a3fdd84f8c8edc795e22e6d][trace][yii\base\View::renderFile] Rendering view file: /app/pb-repo/vendor/yiisoft/yii2/views/errorHandler/callStackItem.php
      2019-12-05 08:35:09 [-][-][d97bb3d28a3fdd84f8c8edc795e22e6d][trace][yii\base\View::renderFile] Rendering view file: /app/pb-repo/vendor/yiisoft/yii2/views/errorHandler/callStackItem.php
      2019-12-05 08:35:09 [-][-][d97bb3d28a3fdd84f8c8edc795e22e6d][trace][yii\base\View::renderFile] Rendering view file: /app/pb-repo/vendor/yiisoft/yii2/views/errorHandler/callStackItem.php
      2019-12-05 08:35:08 [-][-][d97bb3d28a3fdd84f8c8edc795e22e6d][info][application] $_GET = []
  
      $_POST = []
  
      $_FILES = []
  
      $_COOKIE = [
          'CraftSessionId' => 'd97bb3d28a3fdd84f8c8edc795e22e6d'
      ]
  
      $_SESSION = [
          'bd62416aa8538ede709019a5e113eea5__flash' => []
      ]
  
      $_SERVER = [
          'USER' => 'www-data'
          'HOME' => '/var/www'
          'SCRIPT_NAME' => '/index.php'
          'REQUEST_URI' => '/'
          'QUERY_STRING' => ''
          'REQUEST_METHOD' => 'GET'
          'SERVER_PROTOCOL' => 'HTTP/1.0'
          'GATEWAY_INTERFACE' => 'CGI/1.1'
          'REMOTE_PORT' => '50902'
          'SCRIPT_FILENAME' => '//app/pb-repo/web/index.php'
          'SERVER_ADMIN' => 'webmaster@localhost'
          'CONTEXT_DOCUMENT_ROOT' => '/app/pb-repo/web'
          'CONTEXT_PREFIX' => ''
          'REQUEST_SCHEME' => 'http'
          'DOCUMENT_ROOT' => '/app/pb-repo/web'
          'REMOTE_ADDR' => '172.17.0.1'
          'SERVER_PORT' => '80'
          'SERVER_ADDR' => '172.17.0.5'
          'SERVER_NAME' => 'pb.local'
          'SERVER_SOFTWARE' => 'Apache/2.4.10 (Debian)'
          'SERVER_SIGNATURE' => ''
          'PATH' => '/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin'
          'HTTP_COOKIE' => 'CraftSessionId=d97bb3d28a3fdd84f8c8edc795e22e6d'
          'HTTP_UPGRADE_INSECURE_REQUESTS' => '1'
          'HTTP_ACCEPT_ENCODING' => 'gzip, deflate, br'
          'HTTP_ACCEPT_LANGUAGE' => 'en-GB,en;q=0.5'
          'HTTP_ACCEPT' => 'text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8'
          'HTTP_USER_AGENT' => 'Mozilla/5.0 (Macintosh; Intel Mac OS X 10.13; rv:70.0) Gecko/20100101 Firefox/70.0'
          'HTTP_CONNECTION' => 'close'
          'HTTP_X_FORWARDED_PROTO' => 'https'
          'HTTP_X_FORWARDED_HOST' => 'pb.local'
          'HTTP_X_FORWARDED_FOR' => '192.168.95.1'
          'HTTP_X_REAL_IP' => '192.168.95.1'
          'HTTP_HOST' => 'pb.local'
          'proxy-nokeepalive' => '1'
          'HTTPS' => 'on'
          'FCGI_ROLE' => 'RESPONDER'
          'PHP_SELF' => '/index.php'
          'REQUEST_TIME_FLOAT' => 1575534907.7596
          'REQUEST_TIME' => 1575534907
          'ALLOW_UPDATES' => '1'
          'ALLOW_ADMIN_CHANGES' => '1'
          'BACKUP_ON_UPDATE' => '0'
          'DEV_MODE' => '1'
          'ENABLE_TEMPLATE_CACHING' => '1'
          'ENVIRONMENT' => 'dev'
          'IS_SYSTEM_LIVE' => '1'
          'RUN_QUEUE_AUTOMATICALLY' => '1'
          'SECURITY_KEY' => '••••••••••••••••••••••••••••••••••••••••'
          'SITE_NAME' => ''
          'DB_DRIVER' => 'mysql'
          'DB_SERVER' => 'localhost'
          'DB_USER' => 'root'
          'DB_PASSWORD' => '••••'
          'DB_DATABASE' => 'local'
          'DB_SCHEMA' => 'public'
          'DB_TABLE_PREFIX' => ''
          'DB_PORT' => '4095'
          'ASSETS_URL' => ''
          'UPLOADS_URL' => '/uploads/'
          'SITE_URL' => 'https://pb.local/'
          'WEB_ROOT_PATH' => '.'
          'PUBLIC_PATH' => './web/'
          'DEFAULT_SITE_URL' => 'https://pb.local'
      ]
  
  ```
  
  So it seems to be connecting OK, showing tables, loading some modules, starting the session, and then returning the httpException error.
  
  **Tags:** craft3, error-message
  
  > **Comments:**
  > **username_1**: I'd recommend [turning on `devMode`](https://docs.craftcms.com/v3/config/config-settings.html#devmode) for the development environment to get more information about the error, and checking `storage/logs/web.log` for a stack trace.  
  > **username_0**: I've added the most recent output from `web.log`.  
  > **username_1**: Also worth looking at your table names to ensure it's not [using a `tablePrefix`](https://docs.craftcms.com/v3/config/db-settings.html) (if your tables all begin with something like `craft_`, then you may need to include this in your database config / `.env`.  
  > **username_0**: That was it! There was a table prefix but I hadn't bothered to look closely at the tables after I imported the database.  
  > **username_2**: I had a similar problem, and found that my database user was not set up with proper permissions. I found this in the logs, very helpful.  
  
  ---
  
  ## 2 answers
  
  ### Answer by username_1 on 2019-12-06. Score: 1 | Accepted answer
  
  > This answer was contributed after troubleshooting in comments on the original question.
  
  This error can appear for a variety of reasons, but most commonly when Craft believes it isn't installed.
  
  The installation process begins at `/admin/install`, but is dependent upon the [`cpTrigger`](https://docs.craftcms.com/v3/config/config-settings.html#cptrigger) config value. That this page wasn't accessible (or, more specifically, produced the same error instead the Admin or installation wizard) led the asker to conclude that the config value had been updated by the prior developer.
  
  Craft may believe it isn't installed if it can't find the expected tables—sometimes complicated by using a [`tablePrefix` setting](https://docs.craftcms.com/v3/config/db-settings.html#tableprefix), in the database configuration. This setting exists in the event you need to maintain more than one Craft install side-by-side, in the same database.
  
  In this case, a combination of these two settings made it difficult to tell why Craft was producing the `503` error.
  
  
  ---
  
  ### Answer by username_3 on 2019-12-05. Score: 4
  
  Try accessing the CP-Panel, in most cases this error occurs due to config files not being set correctly, thus not allowing craft to connect to the DB.
  
  If you get the installer page when accessing the CP-Pannel, that means it's most likely not able to access the DB with your current configs.
  
  Usually the URL would be my-host.com/backstage
  however this may differ based on your `cpTrigger` config value in `config/general.php`.
  
  Edit: `devMode` should be set to `true` in `config/general.php`.
  
  If this doesn't resolve the issue, try clearing your entire logs folder, calling your page and then uploading those log files as a zip file to any file hoster so we can take closer look at it, your current output from your web.log doesn't show too much...
  
  > **Comments:**
  > **username_1**: `admin` is the default `cpTrigger` value—might be worth updating, granted most installs will be configured as such, out of the box. Otherwise, great recommendations, thorough answer!   
  > **username_0**: This was another stumbling block. The cpTrigger had been set to a different value so I was getting the same error when trying to access the default /admin.  
  
  ---
  
  