Hi, Till, and thanks for the thorough response.
Dont remove the immutable attribute on servers that allow access by ftp client to sites for your customers. The immutable bit is required for security reasons.
I see. I didn't realize that this feature was added with ISPConfig 3.0.5. It's a relief to know that ISPC set the immutable flags intentionally. I won't remove them in the future.
Is there any way to re-apply these settings (such as toggling the feature on and off in the ISPC interface)?
You should consider to reinstall the php cgi / fcgi packages and their dependencies.
What process do you recommend? Something like this?
apt-get install --reinstall php5 php5-dev php5-common php5-cli php5-cgi libapache2-mod-fcgid apache2-suexec libapache2-mod-suphp
From what I understand, using --reinstall doesn't touch any of the dependencies, though. And frankly, I'm a little hesitant to uninstall any dependencies, as some of them are critical, core packages (right?).
Maybe the first thing to try (before trying to reinstall packages) is to look at the phpinfo() output for the ISPC vhost and see what (if anything) appears related to zlib.
Thoughts? Thanks again for your help!