APT - HowTo's

1. get the exact package name :
   dpkg -l | awk '/fpm/ {print $1" "$2}'

   ii php-fpm
   ii php8.1-fpm

2. list its configuration files :
   dpkg --status php8.1-fpm

   
   Conffiles:
    /etc/apache2/conf-available/php8.1-fpm.conf b1e43a02b16bef4f689f6a32eaf8c3a9
    /etc/init.d/php8.1-fpm 40246d5e9590bae90b133167b9bfc118
    /etc/logrotate.d/php8.1-fpm 4bbd87237b3b0883169be0d7f856aad4
    /etc/php/8.1/fpm/php-fpm.conf 75494c14cd7739481ba87d225e031b49
    /etc/php/8.1/fpm/pool.d/www.conf 0e7522a4780a6e196ba34653d7f18ada
   

3. remove / disable those you want to reinstall :

   mv /etc/php/8.1/fpm/php-fpm.conf{,_DELETEME}
   mv /etc/php/8.1/fpm/pool.d/www.conf{,_DELETEME}

4. (re)install the package's missing files :
   apt install --reinstall -o Dpkg::Options::="--force-confmiss" php8.1-fpm

1. retrieve the name of the package that created php.ini :
   dpkg -S php.ini

   php8.1-common: /usr/lib/php/8.1/php.ini-production
   php8.1-common: /usr/lib/php/8.1/php.ini-development
   php8.1-common: /usr/lib/php/8.1/php.ini-production.cli

   answer : php8.1-common
2. check it by listing the package contents :
   dpkg -L php8.1-common | grep php.ini

   /usr/lib/php/8.1/php.ini-development
   /usr/lib/php/8.1/php.ini-production
   /usr/lib/php/8.1/php.ini-production.cli

3. in this specific case, /etc/php/8.1/cgi/php.ini was copied from /usr/lib/php/8.1/php.ini-production.cli. View differences between files :
   diff /usr/lib/php/8.1/php.ini-production.cli /etc/php/8.1/cgi/php.ini

   503c503
   < display_errors = Off
   ---
   > display_errors = On
   846c846
   < ;upload_tmp_dir =
   ---
   > upload_tmp_dir = /path/to/some/dir

4. so, I can either
   • undo changes manually
     I've simplified the changes made to /etc/php/8.1/cgi/php.ini for this article, things are never that simple in real life .
   • overwrite the file I changed :
     cp /usr/lib/php/8.1/php.ini-production.cli /etc/php/8.1/cgi/php.ini

• Although you may configure this in apt's main configuration file /etc/apt/apt.conf, using a dedicated file such as /etc/apt/apt.conf.d/proxy.conf is cleaner.
• Depending on the proxy type :
  • proxy without authentication :
    Acquire::http::Proxy "http://12.34.56.78:1234/";
  • otherwise :
    Acquire::http::Proxy "http://stuart:P@ssw0rd@12.34.56.78:1234/";
  • HTTPS proxy :
    Acquire::https::Proxy "http://12.34.56.78:1234/";
• Alternate syntax :

  Acquire {
  	HTTP::proxy  "http://12.34.56.78:1234/";
  	HTTPS::proxy "http://12.34.56.78:1234/";
  	}

• proxyAddress='12.34.56.78'; proxyPort='1234'
  cat << EOF > /etc/apt/apt.conf.d/proxy.conf
  Acquire::http::Proxy  "http://$proxyAddress:$proxyPort/";
  Acquire::https::Proxy "http://$proxyAddress:$proxyPort/";
  EOF

hold the package packageName :

list packages currently on hold :

un-hold the package packageName :