After submitting, I got a generic error message:
INTERNAL APPLICATION ERROR

Can you please temporarily edit config_defaults_inc.php, and set $g_show_detailed_errors = ON; then try the installation again.
The error page should display a stack trace, please report that here (be careful to mask any sensitive information)

Your connection test mentions that there is 1 table in the DB, what is it ?

I registered a freehosting, where I was able to generate SQL queries, but it also failed.
[...]
-- Schema step 159
0001061 - Duplicate key name 'idx_bug_rev_id_time'

That index should have been dropped at step 154.

INTERNAL APPLICATION ERROR

Call to undefined function shell_exec()

Detailed error information
Full path: /data/web/virtuals/368768/virtual/www/subdom/mantis/core/error_api.php
Line number: 95
Stack trace
#   Filename    Line    Class   Type    Function    Args
0   /data/web/virtuals/368768/virtual/www/subdom/mantis/admin/install.php   498 -   -   url_get <string>'https://mantis.vwg-displays.eu/subdom/mantis/'

This is strange, because I tried to set $g_path to 'https://mantis.vwg-displays.eu/' as is supposed to.

Regarding the DB test, I created one table (which does not interfere with mantis) to test the same credentials (server/login/password/db) I also use for mantis.

OK so you seem to be hitting a variant of 0034783.

I tried to set $g_path to 'https://mantis.vwg-displays.eu/' as is supposed to.

This is not the issue. The problem is a shortcoming of url_get() function, combined with your system's PHP config, which I guess has the following characteristics:

• allow_url_fopen = OFF
• curl extension not installed
• shell_exec disabled

The last point causes an error as url_get() never considered that shell_exec() would be unavailable. Clearly, yet another shortcoming of that api, which needs to be fixed as mentioned in 0034783:0069295.

As a workaround, you can try one of these approaches:

• installing curl extension

• patch url_get() function in core/url_api.php, so it does not try to execute shell_exec() if the function is not present, as follows:

  
  diff --git a/core/url_api.php b/core/url_api.php
  index bb4962baa..77ac9d673 100644
  --- a/core/url_api.php
  +++ b/core/url_api.php
  @@ -74,6 +74,10 @@ function url_get( $p_url ) {
      }
  
      # Last resort system call

• $t_url = escapeshellarg( $p_url );
• return shell_exec( 'curl ' . $t_url );
• if( function_exists( 'shell_exec' ) ) {
• $t_url = escapeshellarg( $p_url );
• return shell_exec( 'curl ' . $t_url );
• }
• return null;

• replace the $t_page_contents = url_get( $f_path ); at line by $t_page_contents = null;

Then the installer will show you a warning, but the installation should continue.

Let me know how it goes.

PR https://github.com/mantisbt/mantisbt/pull/2117 implements a function_exists() check to prevent the error from occuring - url_get() will just return null if shell_exec() is not available.

Hello,

I have allow_url_fopen = ON and CURL installed, only shell_exec is disabled (it seems to be a common practise for some webhosting services).

It seems everything runs fine after the patch.

Thank you very much!

I have allow_url_fopen = ON and CURL installed

Then it's a bit strange that url_get() would fall back to calling shell_exec()... But anyway if it works for you now then it's good enough for me.

Thanks for the feedback, I'll merge the PR soon.