Comment 5 for bug 63707

Till Kamppeter (till-kamppeter) wrote :

The problem was introduced by the following Debian change:

cupsys (1.2.4-2) unstable; urgency=low

  [ Kenshi Muto ]
  * PPD transition to /usr/share/ppd is mostly finished.
    Now I remove old symlink /usr/share/ppd/cups-transitional-dir and
    /usr/share/cups/cups-included. (closes: #381266, #383291)
  * Update debconf translations:
    - Brazilian Portuguese (closes: #389222)
  * Tried to solve the backend permission problem. CUPS scheduler
    uses a permission and owner information of backend program.
    - Install ipp and lpd as mode 0700.
    - Create backend links as hardlink instead of symlink.

I do not know really why this was done in the Debian package, the IPP backend works also as normal user. For the LPD backend this is correct for a distro which runs CUPS as root (Debian), as the LPD backend has to run as root (Ubuntu uses SUID root for it).

Setting a backend to 0700 mode and to owner root is the (documented) method of CUPS 1.2, that a backend is run as root. By default, CUPS 1.2 runs backends as the user "lp". This naturally works only if CUPS itself runs as root (and in Ubuntu CUPS does not run as root).