I config my vps step by step with the help of lincode libery:https://library.linode.com/hosting-website.
My OS is ubuntu 13.10.when installing PHP,at the last step: sudo apt-get install php5-suhosin,I get an error:
Package php5-suhosin is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source

E: Package 'php5-suhosin' has no installation candidate

I do like this to update:apt-get update,but still failed.How to resolve this problem?

Suhosin is a dead project it's not been touched in 2 years and is incompatible with php 5.4+ it was removed in ubuntu 13.04.

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thanks your reply.i come back to ubuntu 12.04 and there is no problem.

I've also hit upon this problem with Ubuntu Saucy. Is it advisable to install the Suhosin package to harden PHP scripts or is this now obsolete for PHP > 5.2 ? Is there an alternative package for PHP security or would I need to downgrade my Ubuntu version to be able to install Suhosin (undesirable).

One last thing, wouldn't it be a good idea to update the Linode start guides regarding all this as it a causes a fair bit of confusion