ufed edits the USE flag settings in your make.conf file only. It can not be used to edit your package.use file.
If you have two make.conf files, /etc/make.conf and /etc/portage/make.conf, ufed reads the first, overrides its settings with the second, and writes changes to the second.
If /etc/portage/make.conf is a directory, ufed will parse all files in this directory recursively, omitting files that begin with a Changes are written to the last file found, overriding all others.
What are USE flags?
The USE settings system is a flexible way to enable or disable various features at package build-time on a global level and for individual packages. This allows an administrator to control how packages are built in regards to the optional features which can be compiled into those packages.
For instance, packages with optional GNOME support can have this support disabled at compile time by disabling the "gnome" USE flag. Enabling the "gnome" USE flag would enable GNOME support in these packages.
The effect of USE flags on packages is dependent on whether both the software itself and the package ebuild supports the USE flag as an optional feature. If the software does not have support for an optional feature then the corresponding USE flag will obviously have no effect.
Also many package dependencies are not considered optional by the software and thus USE flags will have no effect on those mandatory dependencies.
A list of USE keywords used by a particular package can be found by checking the IUSE line in any ebuild file or by using "equery" from gentoolkit.
See http://www.gentoo.org/doc/en/handbook/handbook-x86.xml?part=2&chap=2 for more information on USE flags.
Please also note that if UFED describes a flag (Unknown) it generally means that it is either a spelling error in one of the three configuration files or it is not an officially sanctioned USE flag. Sanctioned USE flags can be found in /usr/portage/profiles/use.desc and in /usr/portage/profiles/use.local.desc.
What are global and local USE flags?
Global USE flags are called such because they represent functionality that is found in a wider variety of packages. For example, the global flag "cjk" is about adding / not adding support for Eastern-Asian languages, which affects a multitude of various packages. Global flags are described in /usr/portage/profiles/use.desc.
Local USE flags are unique package-wise, because the functionality they stand for is only found in that particular package and no other. See /usr/portage/profiles/use.local.desc for a full, per-package listing of all local USE flags.
It still happens that a flag which is defined as global is also defined as local for one or more packages. That is because the general definition of the global flag takes on specialized semantics in some particular package. It also occurs that multiple packages define a local flag of the same name - the meaning of the flag differs, however, for each package.
What are Masked and Forced flags?
ufed allows to view the descriptions of flags that are either masked or forced.
If a USE flag does not apply to your system, or is highly experimental, it is
"masked" and can not be enabled.
If a USE flag is mandatory for your system or for a specific package, it is "forced" and can not be disabled.
Flags that are masked or forced globally have their names displayed in
parentheses, and are prefixed with a '-' if they are masked. If one of these
flags is set in your make.conf, you can remove it with ufed.
If a flag is only masked or forced for specific packages, a lower case 'm' or 'f' in the defaults column (see "Display layout" below) indicates this.
ufed will present you with a list of descriptions for each USE flag. If a description is too long to fit on your screen, you can use the Left and Right arrow keys to scroll the descriptions. Alternatively you can change the description to show a reduced variant using the F10 key, or change the display to wrap long lines into multiple lines using the F11 key.
Use the Up and Down arrow keys, the Page Up and Page Down keys, the Home and End keys, or start typing the name of a flag to select it. Use the space bar to toggle the setting.
You can apply various filters on the flags to display. The text of the bottom line buttons show, which filter the button (or key press) will switch to.
F5: Toggle display of local / global / all flag descriptions.
F6: Toggle display of flags supported by at least one installed package / supported by no installed package / all flags.
F7: Toggle display of masked and forced flags / flags that are neither masked nor forced / all flags.
The default is to display all flags that are neither masked nor forced.
You can change the way the descriptions are displayed. The text of the bottom line buttons show, which way the button (or key press) the display will change to.
F9: Toggle the order of the affected package list and the description.
F10: Toggle whether to display the full description or a stripped version.
F11: Enable / disable wrapping of long lines.
The stripped version has various wordings like "Enables support for" or "Build and install the" at the beginning of the description removed. Although somewhat crippled, the descriptions key information then needs less space and allows, with switched order of the package list and the description, to determine a flags meaning without scrolling the text in most cases; even on low resolution displays.
The default is to display the full description preceded by the list of affected packages.
Below the list of descriptions an indicator line is displayed that shows the
current setting of all filters and settings.
The order and layout is:
glob : Global USE flags are shown.
loca : Local USE flags are shown.
all : All USE flags are shown.
inst : USE flags affecting installed packages are shown.
noti : USE flags affecting not installed packages are shown.
all : All USE flags are shown
mask : Masked and forced USE flags are shown
norm : USE flags that are neither masked nor forced are shown.
all : All USE flags are shown.
left : The list of affected packages is shown left of the description.
righ : The list of affected packages is shown right of the description.
orig : The original full description is shown.
stri : The stripped version of the description is shown.
long : The original one-line layout with horizontal scrolling.
wrap : Wrapped lines that do not need horizontal scrolling.
If ncurses is installed with the "gpm" use flag enabled, you can use your mouse to navigate and to toggle the settings, too.
After changing flags, press the Return or Enter key to save your USE flag setup to make.conf, or press Escape to revert your changes.
Note: Depending on your system, you may need to wait a second before ufed detects the Escape key or mouse clicks; in some cases, you can use the ncurses environment variable ESCDELAY to change this. See ncurses(3X) for more info.
ufed attempts to show you where a particular use setting came from, and what its scope and state is.
Each line consists of the following elements:
(s) flag |DPC|Si| (packages) description
If the character in any of the D, P or C column is a + then that USE flag was set in that file(s), if it is a space then the flag was not mentioned in that file(s) and if it is a - then that flag was unset in that file(s).
Flags marked as [+] or [-] will be saved in your make.conf when you leave the program by hitting the 'Enter' key.
You can change the order of the (packages) and the description with the F9 key.