When I instal nextgen-gallery
plugins. This error message appears
Downloading update from https://downloads.wordpress.org/plugin/nextgen-gallery.zip…
Unpacking the update…
Could not create directory.
How can I fix this problem ?
This is a permissions issue. Ensure the directory is writable by apache. Plugins are unpacked into the wp-content/plugins directory, so I would first attempt writing to the directory as apache:
sudo -u apache touch /path/to/wp-content/plugins/test.txt
Set permissions accordingly to correct the issue. You can read about permissions here: https://www.pluralsight.com/blog/it-ops/linux-file-permissions
You can read about the correct file permission scheme for Wordpress here: https://wordpress.org/support/article/changing-file-permissions/