server:~# apt-get install php5-xsl
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following package was automatically installed and is no longer required:
  libc-client2007b
Use 'apt-get autoremove' to remove them.
The following extra packages will be installed:
  apache2-mpm-prefork apache2.2-bin apache2.2-common libapache2-mod-php5 libapr1 libaprutil1 libaprutil1-dbd-sqlite3 libaprutil1-ldap libc-client2007e liblqr-1-0 libltdl7
  libmagickcore3 libmagickwand3 libmysqlclient16 libonig2 libpcre3 libqdbm14 mysql-common php5-adodb php5-cgi php5-cli php5-common php5-curl php5-gd php5-imagick php5-imap
  php5-mcrypt php5-mysql php5-suhosin
Suggested packages:
  uw-mailutils libmagickcore3-extra
The following packages will be REMOVED:
  apache2-mpm-worker php5-mhash
The following NEW packages will be installed:
  apache2-mpm-prefork apache2.2-bin libapache2-mod-php5 libaprutil1-dbd-sqlite3 libaprutil1-ldap libc-client2007e liblqr-1-0 libltdl7 libmagickcore3 libmagickwand3
  libmysqlclient16 libonig2 libqdbm14 php5-suhosin php5-xsl
The following packages will be upgraded:
  apache2.2-common libapr1 libaprutil1 libpcre3 mysql-common php5-adodb php5-cgi php5-cli php5-common php5-curl php5-gd php5-imagick php5-imap php5-mcrypt php5-mysql
15 upgraded, 15 newly installed, 2 to remove and 434 not upgraded.
Need to get 0 B/20.7 MB of archives.
After this operation, 32.1 MB of additional disk space will be used.
Do you want to continue [Y/n]? Y
E: Could not perform immediate configuration on 'apache2-mpm-prefork'. Please see man 5 apt.conf under APT::Immediate-Configure for details. (2)









   Immediate-Configure
           Defaults to on which will cause APT to install essential and important packages as fast as possible in the install/upgrade operation. This is done to limit the
           effect of a failing dpkg(1) call: If this option is disabled APT does treat an important package in the same way as an extra package: Between the unpacking of the
           important package A and his configuration can then be many other unpack or configuration calls, e.g. for package B which has no relation to A, but causes the dpkg
           call to fail (e.g. because maintainer script of package B generates an error) which results in a system state in which package A is unpacked but unconfigured - each
           package depending on A is now no longer guaranteed to work as their dependency on A is not longer satisfied. The immediate configuration marker is also applied to
           all dependencies which can generate a problem if the dependencies e.g. form a circle as a dependency with the immediate flag is comparable with a Pre-Dependency. So
           in theory it is possible that APT encounters a situation in which it is unable to perform immediate configuration, errors out and refers to this option so the user
           can deactivate the immediate configuration temporarily to be able to perform an install/upgrade again. Note the use of the word "theory" here as this problem was
           only encountered by now in real world a few times in non-stable distribution versions and was caused by wrong dependencies of the package in question or by a system
           in an already broken state, so you should not blindly disable this option as the mentioned scenario above is not the only problem immediate configuration can help
           to prevent in the first place. Before a big operation like dist-upgrade is run with this option disabled it should be tried to explicitly install the package APT is
           unable to configure immediately, but please make sure to report your problem also to your distribution and to the APT team with the buglink below so they can work
           on improving or correcting the upgrade process.