If you get following error while installing Joomla components or plugins,
It was not possible to copy the selected file. JInstaller::install: Failed to copy file: /var/www/localhost/htdocs/tmp/install_4d621e648af3f/plg_sslredirect/sslredirect.php to /var/www/localhost/htdocs/plugins/system/sslredirect.php
You can resolve this by changing permissions (chmod to 777) on following directories in your Joomla website.
chmod 777 /tmp chmod 777 /plugins/content chmod 777 /plugins/system
Install From Directory Solution
Using the second Box inside Admin Panel of Joomla on Extensions > Install / Uninstall screen
you can simply unzip the files of the plugin and upload the folder in the path shown in the “Install Directory:” field.
Add the path of your plugin folder to this install directory path “/var/www/localhost/htdocs/tmp” will become this
Hope that helps.