Parfois, portage peut signaler une collision de fichiers et refuser la poursuite de l’installation d’un package :

>>> Installing sys-libs/timezone-data-2009c
* checking 1712 files for package collisions
1000 files checked ...
* This package will overwrite one or more files that may belong to other
* packages (see list below). You can use a command such as `portageq
* owners / <filename>` to identify the installed package that owns a
* file. If portageq reports that only one package owns a file then do
* NOT file a bug report. A bug report is only useful if it identifies at
* least two or more packages that are known to install the same file(s).
* If a collision occurs and you can not explain where the file came from
* then you should simply ignore the collision since there is not enough
* information to determine if a real problem exists. Please do NOT file
* a bug report at unless you report exactly which
* two packages install the same file(s). Once again, please do NOT file
* a bug report unless you have completely understood the above message.
* Detected file collision(s):
*     /usr/bin/tzselect
*     /usr/sbin/zic
*     /usr/sbin/zdump
*     /usr/share/zoneinfo/GB
* Package 'sys-libs/timezone-data-2009c' NOT merged due to file
* collisions. If necessary, refer to your elog messages for the whole
* content of the above message.

Les fichiers en collision ont été installés par un autre package; il refuse donc de les supprimer. Si cela est nécessaire, il est possible de le débloquer :

# COLLISION_IGNORE="/usr" emerge -av timezone-data