Gentoo

eix

eix -c -I --world

... list packages that are not dependencies (not -1)

gentoolkit

equery belongs /usr/bin/xmms

... show which package /usr/bin/xmms belongs to

equery depends xine-lib

... show the packages depending on xine-lib

equery files --tree gentoolkit

... lists installed files in a tree format

equery hasuse qt3 qt4x

... searches for installed packages that use the qt3 or qt4 USE flags

equery uses firefox

... list USE flags and their descriptions for the 'firefox' port

portage

ebuild firefox-17.0.ebuild digest

... updates the digest for the given ebuild

emerge -uavDNt --with-bdeps=y @world

... updates everything, including B-deps

emerge -e @world

... rebuilds the entire system

emerge -pvc dev-lang/python:3.11

... displays why a dependency can not be "dep. cleaned"

quickpkg www-client/firefox

... makes a binary package of a existing package (www-client/firefox)

Hacks

GRUB on EFI

Assuming EFI partition mounted on /efi/

Some motherboard manufacturers with poor UEFI implementations seem to only support the /EFI/BOOT directory location for the .EFI file in the EFI System Partition (ESP).
The GRUB installer can create the .EFI file in this location automatically by appending the --removable option to the install command.
Ensure the ESP has been mounted before running the following command; presuming it is mounted at /efi (as defined earlier), run:

grub-install --target=x86_64-efi --efi-directory=/efi --removable

... creates the 'default' directory defined by the UEFI specification, and then creates a file with the default name: BOOTX64.EFI.

ssh-agent session

Insert ssh-agent in front of each session

Edit /etc/lightdm/Xsession and replace:

exec ${command}

with

exec /usr/bin/ssh-agent ${command}