Modifying USE flags in Gentoo

To modify the global USE flags, set the USE variable in /etc/make.conf

You can set USE flags for individual packages by specifying the package name and USE flag, in /etc/portage/package.use (the file or directory may not exist).

Eg of /etc/portage/package.use

dev-db/mysql berkdb -java[/code]

The above example disables java use flag and enables berkdb for package dev-db/mysql.
If you want only a temporary USE flag during emerge of just the current package, you can specify the flag on the same command line where you specify the emerge:
USE="-java" emerge seamonkey[/code]

To view the current USE flags, run:
emerge --info
Once some USE flags have been set, one must make Portage see the new flags, with:
emerge --update --deep --newuse world[/code]