We have briefly encountered emerge in the previous chapter, but not to the extent that you are now able to work with it to its fullest potential. We will fix that right now ;-)

emerge is the command used to install, remove, query and maintain software packages. It is a front-end for ebuild; people interested in becoming Gentoo professionals will learn how to use ebuild later on. For now, we will focus on emerge as it has functionality that ebuild lacks (such as resolving dependencies, searching the Portage tree, etc.).

Since emerge is the most important tool for Gentoo users, it has an extensive manpage you can read by issuing man emerge. You can also view the in-command help by running emerge --help.

# man emerge
# emerge --help

Before we continue describing emerge, let us first take a look at the Portage Tree. Go to /usr/portage and do a listing of the available directories.

# cd /usr/portage; ls --classify
(The --classify will append a special character to note the filetype)
app-admin/       dev-ml/            gnome-libs/     net-print/
app-arch/        dev-perl/          gnome-office/   net-wireless/
app-benchmarks/  dev-php/           header.txt      net-www/
app-cdr/         dev-python/        incoming/       net-zope/
app-crypt/       dev-ruby/          jython/         packages/
app-dicts/       dev-tcltk/         kde-apps/       profiles/
app-doc/         dev-tex/           kde-base/       releases/
app-editors/     dev-util/          kde-i18n/       scripts/
app-emacs/       distfiles/         kde-libs/       sec-policy/
app-emulation/   eclass/            licenses/       skel.ChangeLog
app-games/       experimental/      media-fonts/    skel.ebuild
app-gnustep/     files/             media-gfx/      skel.metadata.xml
app-i18n/        fresco-base/       media-libs/     snapshots/
app-misc/        games-action/      media-plugins/  sys-apps/
app-office/      games-arcade/      media-radio/    sys-build/
app-pda/         games-board/       media-sound/    sys-cluster/
app-portage/     games-emulation/   media-tv/       sys-devel/
app-sci/         games-engines/     media-video/    sys-fs/
app-shells/      games-fps/         metadata/       sys-kernel/
app-text/        games-kids/        net-analyzer/   sys-kmods/
app-vim/         games-misc/        net-apache/     sys-libs/
app-xemacs/      games-mud/         net-dialup/     unix2tcp/
berlin-base/     games-puzzle/      net-dns/        x11-base/
dev-ada/         games-roguelike/   net-firewall/   x11-libs/
dev-cpp/         games-rpg/         net-fs/         x11-misc/
dev-db/          games-server/      net-ftp/        x11-plugins/
dev-dotnet/      games-simulation/  net-im/         x11-terms/
dev-embedded/    games-sports/      net-irc/        x11-themes/
dev-games/       games-strategy/    net-libs/       x11-wm/
dev-haskell/     games-util/        net-mail/       xfce-base/
dev-java/        glep/              net-misc/       xfce-extra/
dev-lang/        gnome-apps/        net-nds/
dev-libs/        gnome-base/        net-news/
dev-lisp/        gnome-extra/       net-p2p/

As you can see, the Portage tree has several subdirectories. Most of them are the categories in which the Gentoo packages, called ebuilds, reside. Take a look at, for instance, app-office:

# cd app-office; ls --classify
abiword/     gnotime/   kmymoney2/  ooodi/              plan/     timestamp.x
dia/         gnucash/   koffice/    oooqs/              qhacc/
dia2code/    gnumeric/  lxbank/     openoffice/         sc/
facturalux/  ical/      lyx/        openoffice-bin/     scribus/
gaby/        kbudget/   mdbtools/   openoffice-ximian/  siag/
gnofin/      khacc/     mrproject/  phprojekt/          texmacs/

Inside a category you will find the packages belonging to that category, with a seperate directory for each package. Let us take a look at the openoffice package:

# cd openoffice; ls --classify
ChangeLog  files/        openoffice-1.0.3-r1.ebuild  openoffice-1.1.0-r2.ebuild
Manifest   metadata.xml  openoffice-1.1.0-r1.ebuild  openoffice-1.1.0.ebuild

Remember that we told you that a Gentoo package is called an ebuild? Well, in the example directory four of such ebuilds are stored. Their naming is almost identical: they only differ in the version name. You are free to view the contents of such a package: they are plain scripts. We will not discuss it right now as it isn't important to know if you plan on just using Gentoo.

The other files are the ChangeLog (which contains a listing of all the changes done to the ebuilds), Manifest (which contains the checksums and permissions of all the files in the directory) and metadata.xml (which contains more information about the package, such as the responsible development group -- called herd and a more extensive description).

Inside the files directory you will find extra files, needed by Portage: digests (checksums and permissions of the files needed by a single version of the package), patches, example configuration files, etc.

# cd files; ls --classify
1.0.3/  digest-openoffice-1.0.3-r1  digest-openoffice-1.1.0-r1
1.1.0/  digest-openoffice-1.1.0     digest-openoffice-1.1.0-r2
# cd 1.1.0; ls --classify
fixed-gcc.patch      ooffice-wrapper-1.3
newstlportfix.patch  openoffice-1.1.0-linux-2.6-fix.patch
no-mozab.patch       openoffice-1.1.0-sparc64-fix.patch
nptl.patch

If you go back to the root of the Portage tree (/usr/portage) you will notice that there are other, non-category directories too. We will discuss those later in this chapter.

If you are new to Linux or Gentoo, you might not know what tool you need for what job. To facilitate searching, emerge provides you with a way to search through the available packages on your system. There are two ways you can search through packages: by name, or by name and description.

To search through the Portage tree by name, use emerge search. For instance, to find out more about mozilla:

# emerge search mozilla
Searching...   
[ Results for search key : mozilla ]
[ Applications found : 5 ]
(Some output removed to improve readability)
*  net-www/mozilla
      Latest version available: 1.5-r1
      Latest version installed: 1.4-r3
      Size of downloaded files: 29,153 kB
      Homepage:    http://www.mozilla.org
      Description: The Mozilla Web Browser

*  net-www/mozilla-firebird
      Latest version available: 0.7
      Latest version installed: [ Not Installed ]
      Size of downloaded files: 37,850 kB
      Homepage:    http://www.mozilla.org/projects/firebird/
      Description: The Mozilla Firebird Web Browser
(...)

If you want to include a search through the descriptions too, use the --searchdesc argument:

# emerge --searchdesc mozilla
Searching...   
[ Results for search key : mozilla ]
[ Applications found : 10 ]
(Some output removed to improve readability)
*  dev-libs/nss-3.8
      Latest version available: 3.8
      Latest version installed: 3.8
      Size of downloaded files:  2,782 kB
      Homepage:    http://www.mozilla.org/projects/security/pki/nss/
      Description: Mozilla's Netscape Security Services Library that implements PKI support

As you can see, the output of emerge informs you about the category and name of the package, the available version, the currently installed version, the size of the downloaded files, the homepage and the small description.

You see something new? Yes, downloaded files. When you tell Portage to install a package, it ofcourse needs to have the necessary sources (or precompiled packages) available. It therefor checks the contents of /usr/portage/distfiles (for sourcecode) or /usr/portage/packages/All (for precompiled packages) to see if the necessary files are already available. If not, it downloads the necessary files and places them in those directories.

While browsing through the Portage Tree, you saw that there was a ChangeLog for each package. You can view this ChangeLog with emerge too. Use the --pretend --changelog (-pl in short) options. As an example we will view the ChangeLog entries for gnumeric:

# emerge --pretend --changelog gnumeric

Searching through Portage is nice, but if you don't update your Portage Tree regularly, you will be stuck with the packages and versions available on your system. This means that your system will get outdated pretty soon, and that packages with possible security problems will remain on your system.

There are several ways to update your Portage Tree. The most popular method is by using one of our rsync mirrors. Another one is by using a Portage snapshot (in case a firewall or unavailability of a network prohibits the use of the rsync server).

It is adviseable to first select a fast mirror close to you. You can do this manually (by setting the SYNC variable in /etc/make.conf) or use mirrorselect to do this for you automatically. As the SYNC variable will be discussed later on, we will focus on using mirrorselect. First install mirrorselect by emerging it:

# emerge --usepkg mirrorselect

Now run mirrorselect to automatically select mirrors for you (it will also setup Portage to use a mirror for the sourcecode):

# mirrorselect -a -s3

To update Portage using rsync, simply run emerge sync:

# emerge sync

If this fails (due to network problems, or a firewall), you can try using emerge-webrsync which will download a Portage Tree snapshot using wget. This also means that you can use proxies if you want. We discussed how to setup your system to use proxies during the Gentoo installation.

# emerge-webrsync

Gentoo provides ebuilds, the Gentoo packages if you like. But when you want to install such an ebuild, you can choose between building the package, or using a prebuild package. But what are the advantages/disadvantages of both approaches, and can they be used next to each other?

As you probably have guessed, building packages takes a lot of time (especially if you have little resources or want to build big packages, such as KDE, OpenOffice.org, etc.). By building the package, you can use the USE setting to tweak the package to your system. Ofcourse, you can also define high optimization options (in the CFLAGS and CXXFLAGS variables) to compile the package with.

Using prebuild packages improves the installation time (as no more compilation is needed), but you will lose the advantages of the USE setting and the CFLAGS & CXXFLAGS variables.

As previously stated, prebuild packages are stored in the /usr/portage/packages/All directory, while the sourcecode of the packages are placed in /usr/portage/distfiles. If you have finished installing a package you can remove the package or sourcecode from the respective directory. However, you might want to keep the package/sourcecode of the latest version, just in case you want to reinstall the package (so you don't have to redownload it).

Okay, enough talking, let's cut to the chase. To install a package, you will use the emerge command. If you don't want to use any prebuild packages, you can just use emerge <package-name> or emerge <category>/<package-name>. As an example we'll install gnumeric:

# emerge gnumeric

This will download the sourcecode for you and unpacks, compiles and installs the package on your system. It will also do the same for all the dependencies. If you want to see what dependencies will be installed with it, use the --pretend option (-p in short):

# emerge --pretend gnumeric

If you want to download the sourcecode of the package and its dependencies, but don't want to build the package, use the --fetchonly option (-f in short):

# emerge --fetchonly gnumeric

If you want to see where emerge downloads the sources from, combine the --fetchonly and --pretend options:

# emerge --fetchonly --pretend gnumeric

You can also opt to install a specific version of a package. For instance, if you want to install a gnumeric version older than 1.2 -- for any reason whatsoever :) you would type:

# emerge "<gnumeric-1.2"

Other possibilities are ofcourse ">" (later version) and "=" (the exact version).

When you want to install a prebuild package, you should use the --usepkg option (-k in short). This will use the binary package available in /usr/portage/packages/All if the package and the version of the application you want to install match.

# emerge --usepkg gnumeric

If you want to use the binary package, even if the versions don't match, use --usepkgonly (-K in short).

# emerge --usepkgonly gnumeric

If you don't have the prebuild package on your system yet, you can have emerge download it from a mirror, defined in the PORTAGE_BINHOST variable declared in /etc/make.conf.

To download the binary package in case this package doesn't exist on your system already, use --getbinpkg (-g in short):

# emerge --getbinpkg gnumeric

This will download the package and the package-related information for you and install it on your system, together with the dependencies. If you want to see what dependencies will be installed with it, use the --pretend option (-p in short):

# emerge --ginbinpkg --pretend gnumeric

You can also opt to download the prebuild package (and the package-related information) without checking the information on your local system and without using the prebuild package already on your system (if applicable), use the --getbinpkgonly option (-G in short):

# emerge --getbinpkgonly gnumeric

You can also opt to install a specific version of a package. For instance, if you want to install a gnumeric version older than 1.2 -- for any reason whatsoever :) you would type:

# emerge --usepkg "<gnumeric-1.2"

Other possibilities are ofcourse ">" (later version) and "=" (the exact version).

Portage knows two special tags to denote a set of software packages: system and world. You have already seen the former while installing Gentoo if you didn't use a stage3 installation. To refresh things: system is the collection of core packages, necessary to have a working Gentoo system.

The world tag consists of all software you have installed yourself on your system plus the system information. In other words, every time you emerge a package using emerge <package-name>, the <package-name> is registered in the world file (/var/cache/edb/world). Dependencies are not part of the world file, but we will get to that later.

If you want to update the system packages, use the --update option (-u in short):

# emerge --update system

An identical approach can be used for the world packages:

# emerge --update world

Again, if you want to see what emerge wants to update, use the --pretend option together with the --update option:

# emerge --pretend --update world
(Some output removed to improve readability)
[ebuild     U ] net-misc/wget-1.9-r1 [1.9] 
[ebuild     UD] media-video/dvdauthor-0.5.0 [0.5.3] 
[ebuild     U ] net-analyzer/ethereal-0.9.16 [0.9.14] 

Right next to the word "ebuild" you will notice a letter (or combination of letters) which gives you more information about the package:

• B (blocks) The package listed to the left is blocking the emerge of the package listed to the right
• N (new) The package is new to your system and will be emerged for the first time
• R (reemerge) The package isn't new, but needs to be reemerged
• F (fetch) The package requires that you download the sourcecode manually (for instance due to licencing issues)
• U (update) The package already exists on your system but will be upgraded
• UD (downgrade) The package already exists on your system but will be downgraded
• U- (slot warning) The package you have installed on your system is listed as a package that can not coexist with a different version, but your update does. The update will be installed and the older version will be removed.

In certain cases, an update may mean a downgrade (i.e. install an older version instead of a newer version). If you don't want this to happen, use the --upgradeonly option (-U in short):

# emerge --update --upgradeonly world

Ofcourse, we are talking here about system and world, but you can perform the same actions for individual software packages.

If you want to remove software from your system, you can use the unmerge option (-C - capital C - in short):

# emerge unmerge gnumeric

If you want to test a removal (but not perform it), you can use --pretend again:

# emerge --pretend unmerge gnumeric

Gentoo places its packages in two possible stadia called ARCH and ~ARCH. Don't take this literally: the stadia depend on the architecture you are using. In other words, for x86-based systems you have x86 and ~x86, for ppc-based systems you have ppc and ~ppc etc.

The ~ARCH stadium means that the package works for the developer in charge of the package, but that the package hasn't been tested thoroughly enough by the community to be placed in ARCH. ~ARCH packages usually go to ARCH after being bugfree for a sufficient amount of time.

Your system will use ARCH packages per default. If you want to live on the edge, don't mind having a broken package once in a while, and you like submitting bugreports to bugs.gentoo.org, then you can opt to use ~ARCH packages. To "move" your system to a ~ARCH-using system, edit the ACCEPT_KEYWORDS variable in /etc/make.conf so that it reads ~ARCH (again: for x86-based systems: ~x86, etc.).

If you want to update your system now, you will notice that a lot of packages will be updated!

When you want to install a package, you might come across the following message:

Calculating dependencies   
!!! all ebuilds that could satisfy <your package> have been masked.

A package can be masked due to two reasons:

1. The package is in ~ARCH while you use ARCH
2. The package is hard-masked explicitly

If the package is masked because of the first reason, and you really want to install it (knowing that there is a reason why it isn't available in ARCH), you can temporarily accept ~ARCH packages:

# ACCEPT_KEYWORDS="~x86" emerge gnumeric

A package is hardmasked if it is listed in /usr/portage/profiles/package.mask. If you read this file, you will also read the reason why the package is hardmasked (it is usually added as a comment). If you want to install the package nevertheless (despite all the possible warnings we could ever throw at your head about "breaking your system", "breaks other packages", or "badly needs testing"), create the /etc/portage/package.unmask file and list the package in it (use the same format as is used in /usr/portage/profiles/package.mask).

Do not alter the /usr/portage/profiles/package.mask file as all changes are undone the next time you update your Portage tree.

Another trick to circumvent the "masked package" problem is to install the package using the full path. This will ignore both the ACCEPT_KEYWORD settings and the package.mask listing.

# emerge /usr/portage/app-office/gnumeric/gnumeric-1.2.0.ebuild

You have a situation when you receive the following error on your screen:

[blocks B     ] gnome-base/bonobo-activation (from pkg gnome-base/libbonobo-2.4.0) 

In the above example, the package bonobo-activation is blocking the emerge of libbonobo. To resolve this issue, remove the bonobo-activation package and continue:

# emerge unmerge bonobo-activation