this should be the mojolicious's problem. normal socket program is ok .

foreaxmple, the following code, close_on_exec works. 
#!/bin/env perl
use Modern::Perl;
use IO::Socket; # or Socket;

$^F=2;

# server
my $server_port = 4444;
my $server = IO::Socket::INET->new(
    LocalPort => $server_port,
    Type => SOCK_STREAM,
    Reuse => 1,
    Listen => 10) 
    or die "Couldn't be a tcp server on port $server_port:$!\n";
my $client;
while($client = $server->accept()){
    say 'client connected ...';
    system('/home/admin/t.sh &>/dev/null &');
    
}

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In reply to Re^2: close_on_exec in Perl : close socket opened in parent process when fork child , is not working by chinaxing
in thread close_on_exec in Perl : close socket opened in parent process when fork child , is not working by chinaxing

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