[cups] CUPS + VPN

[Michael Sweet]

Lisa,

> On Oct 14, 2015, at 2:32 PM, Lisa Marie Maginnis <lisam at fsf.org> wrote:
> 
> Hello,
> 
> We are having issues with CUPS and shared printers over our VPN. The issue is that if a user is not on the VPN when CUPS starts, they are unable to see printers until they restart CUPS by hand. It crossed my mind to add a restart of CUPS to the scripts that run when a client connects to the VPN, but I wanted to ask around to see if there is a CUPS only solution to try first.
> 
> Clients are configured by adding the following line to /etc/cups/client.conf:
> ServerName printserver.example.com
> 
> Is there a way to increase the polling time of the remote cups server? Or maybe a better way to configure CUPS clients for using a remote cups server that might not be there when the system first boots?

The client.conf setting is checked on the startup of every program that uses the CUPS API (actually for every thread in every program ...)  And all of the standard CUPS programs and APIs will retry both the address lookup and connection to the server.

So theoretically an application that is started before the VPN is up *might* not be able to print, but generally speaking that should never happen unless the program is written explicitly to not retry such issues.

So without more information it is difficult to help you here - what software isn't working? Where are the printers not showing up?

........

PS: The ServerName directive in client.conf is officially deprecated for all platforms and explicitly not supported on OS X - sandboxing, AppArmor, SELinux, etc. can all interfere with an application's ability to access remote servers, so its continued use is not recommended.  Other CUPS APIs (cupsEnumDests in particular) can be used by applications to get a dynamic view of available shared printers (from multiple servers); adoption of the newer (4 years old now) APIs has been slow, however... :/

_________________________________________________________
Michael Sweet, Senior Printing System Engineer, PWG Chair