en/handbook/hb-working-portage.xml

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<sections>

<abstract>
This chapter explains the "simple" steps a user definitely needs to know to
maintain the software on his system.
</abstract>

<version>1.65</version>
<date>2008-12-23</date>

<section>
<title>Welcome to Portage</title>
<body>

<p>
Portage is probably Gentoo's most notable innovation in software management.
With its high flexibility and enormous amount of features it is frequently seen
as the best software management tool available for Linux.
</p>

<p>
Portage is completely written in <uri link="http://www.python.org">Python</uri>
and <uri link="http://www.gnu.org/software/bash">Bash</uri> and therefore fully
visible to the users as both are scripting languages.
</p>

<p>
Most users will work with Portage through the <c>emerge</c> tool. This chapter
is not meant to duplicate the information available from the emerge man page. 
For a complete rundown of emerge's options, please consult the man page:
</p>

<pre caption="Reading the emerge man page">
$ <i>man emerge</i>
</pre>

</body>
</section>
<section>
<title>The Portage Tree</title>
<subsection>
<title>Ebuilds</title>
<body>

<p>
When we talk about packages, we often mean software titles that are available to
the Gentoo users through the Portage tree. The Portage tree is a collection of
<e>ebuilds</e>, files that contain all information Portage needs to maintain
software (install, search, query, ...). These ebuilds reside in
<path>/usr/portage</path> by default.
</p>

<p>
Whenever you ask Portage to perform some action regarding software titles, it
will use the ebuilds on your system as a base. It is therefore important that
you regularly update the ebuilds on your system so Portage knows about new
software, security updates, etc.
</p>

</body>
</subsection>
<subsection>
<title>Updating the Portage Tree</title>
<body>

<p>
The Portage tree is usually updated with <uri
link="http://rsync.samba.org/">rsync</uri>, a fast incremental file transfer
utility. Updating is fairly simple as the <c>emerge</c> command provides a
front-end for rsync:
</p>

<pre caption="Updating the Portage tree">
# <i>emerge --sync</i>
</pre>

<p>
If you are unable to rsync due to firewall restrictions you can still update
your Portage tree by using our daily generated Portage tree snapshots. The
<c>emerge-webrsync</c> tool automatically fetches and installs the latest
snapshot on your system:
</p>

<pre caption="Running emerge-webrsync">
# <i>emerge-webrsync</i>
</pre>

</body>
</subsection>
</section>
<section>
<title>Maintaining Software</title>
<subsection>
<title>Searching for Software</title>
<body>

<p>
To search through the Portage tree after software titles, you can use
<c>emerge</c> built-in search capabilities. By default, <c>emerge --search</c>
returns the names of packages whose title matches (either fully or partially)
the given search term.
</p>

<p>
For instance, to search for all packages who have "pdf" in their name:
</p>

<pre caption="Searching for pdf-named packages">
$ <i>emerge --search pdf</i>
</pre>

<p>
If you want to search through the descriptions as well you can use the
<c>--searchdesc</c> (or <c>-S</c>) switch:
</p>

<pre caption="Searching for pdf-related packages">
$ <i>emerge --searchdesc pdf</i>
</pre>

<p>
When you take a look at the output, you'll notice that it gives you a lot of
information. The fields are clearly labelled so we won't go further into their
meanings:
</p>

<pre caption="Example 'emerge --search' output">
*  net-print/cups-pdf
      Latest version available: 1.5.2
      Latest version installed: [ Not Installed ]
      Size of downloaded files: 15 kB
      Homepage:    http://cip.physik.uni-wuerzburg.de/~vrbehr/cups-pdf/
      Description: Provides a virtual printer for CUPS to produce PDF files.
      License:     GPL-2
</pre>

</body>
</subsection>
<subsection>
<title>Installing Software</title>
<body>

<p>
Once you've found a software title to your liking, you can easily install it
with <c>emerge</c>: just add the package name. For instance, to install
<c>gnumeric</c>:
</p>

<pre caption="Installing gnumeric">
# <i>emerge gnumeric</i>
</pre>

<p>
Since many applications depend on each other, any attempt to install a certain
software package might result in the installation of several dependencies as
well. Don't worry, Portage handles dependencies well. If you want to find out
what Portage <e>would</e> install when you ask it to install a certain package,
add the <c>--pretend</c> switch. For instance:
</p>

<pre caption="Pretend to install gnumeric">
# <i>emerge --pretend gnumeric</i>
</pre>

<p>
When you ask Portage to install a package, it will download the necessary source
code from the internet (if necessary) and store it by default in
<path>/usr/portage/distfiles</path>. After this it will unpack, compile and
install the package. If you want Portage to only download the sources without
installing them, add the <c>--fetchonly</c> option to the <c>emerge</c> command:
</p>

<pre caption="Download the sourcecode for gnumeric">
# <i>emerge --fetchonly gnumeric</i>
</pre>

</body>
</subsection>
<subsection>
<title>Finding Installed Package Documentation</title>
<body>

<p>
Many packages come with their own documentation. Sometimes, the <c>doc</c> USE
flag determines whether the package documentation should be installed or not.
You can check the existence of a <c>doc</c> USE flag with the <c>emerge -vp
&lt;package name&gt;</c> command.
</p>

<pre caption="Checking the existence of a doc USE flag">
<comment>(alsa-lib is just an example, of course.)</comment>
# <i>emerge -vp alsa-lib</i>
[ebuild  N    ] media-libs/alsa-lib-1.0.14_rc1  -debug +doc 698 kB
</pre>

<p>
The best way of enabling the <c>doc</c> USE flag is doing it on a per-package
basis via <path>/etc/portage/package.use</path>, so that you get documentation
only for packages that you are interested in. Enabling this flag globally is
known to cause problems with circular dependencies. For more information, please
read the <uri link="?part=2&amp;chap=2">USE Flags</uri> chapter.
</p>

<p>
Once the package installed, its documentation is generally found in a
subdirectory named after the package under the <path>/usr/share/doc</path>
directory. You can also list all installed files with the <c>equery</c> tool
which is part of the <c>app-portage/gentoolkit</c> <uri
link="/doc/en/gentoolkit.xml">package</uri>.
</p>

<pre caption="Locating package documentation">
# <i>ls -l /usr/share/doc/alsa-lib-1.0.14_rc1</i>
total 28
-rw-r--r--  1 root root  669 May 17 21:54 ChangeLog.gz
-rw-r--r--  1 root root 9373 May 17 21:54 COPYING.gz
drwxr-xr-x  2 root root 8560 May 17 21:54 html
-rw-r--r--  1 root root  196 May 17 21:54 TODO.gz

<comment>(Alternatively, use equery to locate interesting files:)</comment>
# <i>equery files alsa-lib | less</i>
media-libs/alsa-lib-1.0.14_rc1
* Contents of media-libs/alsa-lib-1.0.14_rc1:
/usr
/usr/bin
/usr/bin/alsalisp
<comment>(Output truncated)</comment>
</pre>

</body>
</subsection>
<subsection>
<title>Removing Software</title>
<body>

<p>
When you want to remove a software package from your system, use <c>emerge
--unmerge</c>. This will tell Portage to remove all files installed by that
package from your system <e>except</e> the configuration files of that
application if you have altered those after the installation. Leaving the
configuration files allows you to continue working with the package if you ever
decide to install it again.
</p>

<p>
However, a <brite>big warning</brite> applies: Portage will <e>not</e> check if 
the package you want to remove is required by another package. It will however
warn you when you want to remove an important package that breaks your system 
if you unmerge it.
</p>

<pre caption="Removing gnumeric from the system">
# <i>emerge --unmerge gnumeric</i>
</pre>

<p>
When you remove a package from your system, the dependencies of that package
that were installed automatically when you installed the software are left. To
have Portage locate all dependencies that can now be removed, use
<c>emerge</c>'s <c>--depclean</c> functionality. We will talk about this later
on.
</p>

</body>
</subsection>
<subsection>
<title>Updating your System</title>
<body>

<p>
To keep your system in perfect shape (and not to mention install the latest
security updates) you need to update your system regularly. Since Portage only
checks the ebuilds in your Portage tree you first have to update your Portage
tree. When your Portage tree is updated, you can update your system with
<c>emerge --update world</c>. In the next example, we'll also use the
<c>--ask</c> switch which will tell Portage to display the list of packages it
wants to upgrade and ask you if you want to continue:
</p>

<pre caption="Updating your system">
# <i>emerge --update --ask world</i>
</pre>

<p>
Portage will then search for newer version of the applications you have
installed. However, it will only verify the versions for the applications you
have <e>explicitly</e> installed (the applications listed in
<path>/var/lib/portage/world</path>) - it does not thoroughly check their
dependencies. If you want to update <e>every single package</e> on your system,
add the <c>--deep</c> argument:
</p>

<pre caption="Updating your entire system">
# <i>emerge --update --deep world</i>
</pre>

<p>
Since security updates also happen in packages you have not explicitly installed
on your system (but that are pulled in as dependencies of other programs), it 
is recommended to run this command once in a while. 
</p>

<p>
If you have altered any of your <uri link="?part=2&amp;chap=2">USE flags</uri>
lately you might want to add <c>--newuse</c> as well. Portage will then verify
if the change requires the installation of new packages or recompilation of
existing ones:
</p>

<pre caption="Performing a full update">
# <i>emerge --update --deep --newuse world</i>
</pre>

</body>
</subsection>
<subsection>
<title>Metapackages</title>
<body>

<p>
Some packages in the Portage tree don't have any real content but are used to
install a collection of packages. For instance, the <c>kde</c> package will
install a complete KDE environment on your system by pulling in various
KDE-related packages as dependencies.
</p>

<p>
If you ever want to remove such a package from your system, running <c>emerge
--unmerge</c> on the package won't have much effect as the dependencies remain
on the system.
</p>

<p>
Portage has the functionality to remove orphaned dependencies as well, but since
the availability of software is dynamically dependent you first need to update
your entire system fully, including the new changes you applied when changing
USE flags. After this you can run <c>emerge --depclean</c> to remove the
orphaned dependencies. When this is done, you need to rebuild the applications
that were dynamically linked to the now-removed software titles but don't
require them anymore.
</p>

<p>
All this is handled with the following three commands:
</p>

<pre caption="Removing orphaned dependencies">
# <i>emerge --update --deep --newuse world</i>
# <i>emerge --depclean</i>
# <i>revdep-rebuild</i>
</pre>

<p>
<c>revdep-rebuild</c> is provided by the <c>gentoolkit</c> package; don't forget
to emerge it first:
</p>

<pre caption="Installing the gentoolkit package">
# <i>emerge gentoolkit</i>
</pre>

</body>
</subsection>
</section>
<section>
<title>When Portage is Complaining...</title>
<subsection>
<title>About SLOTs, Virtuals, Branches, Architectures and Profiles</title>
<body>

<p>
As we stated before, Portage is extremely powerful and supports many features
that other software management tools lack. To understand this, we explain a few
aspects of Portage without going into too much detail.
</p>

<p>
With Portage different versions of a single package can coexist on a system.
While other distributions tend to name their package to those versions (like
<c>freetype</c> and <c>freetype2</c>) Portage uses a technology called
<e>SLOT</e>s. An ebuild declares a certain SLOT for its version. Ebuilds with
different SLOTs can coexist on the same system. For instance, the
<c>freetype</c> package has ebuilds with <c>SLOT="1"</c> and <c>SLOT="2"</c>.
</p>

<p>
There are also packages that provide the same functionality but are implemented
differently. For instance, <c>metalogd</c>, <c>sysklogd</c> and <c>syslog-ng</c>
are all system loggers. Applications that rely on the availability of "a system
logger" cannot depend on, for instance, <c>metalogd</c>, as the other system
loggers are as good a choice as any. Portage allows for <e>virtuals</e>: each
system logger provides <c>virtual/syslog</c> so that applications can depend on
<c>virtual/syslog</c>.
</p>

<p>
Software in the Portage tree can reside in different branches. By default your
system only accepts packages that Gentoo deems stable. Most new software titles,
when committed, are added to the testing branch, meaning more testing needs to
be done before it is marked as stable. Although you will see the ebuilds for
those software in the Portage tree, Portage will not update them before they are
placed in the stable branch.
</p>

<p>
Some software is only available for a few architectures. Or the software doesn't
work on the other architectures, or it needs more testing, or the developer that
committed the software to the Portage tree is unable to verify if the package
works on different architectures.
</p>

<p>
Each Gentoo installation adheres to a certain <c>profile</c> which contains,
amongst other information, the list of packages that are required for a system 
to function normally.
</p>

</body>
</subsection>
<subsection id="blocked">
<title>Blocked Packages</title>
<body>

<pre caption="Portage warning about blocked packages (with --pretend)">
[blocks B     ] mail-mta/ssmtp (is blocking mail-mta/postfix-2.2.2-r1)
</pre>

<pre caption="Portage warning about blocked packages (without --pretend)">
!!! Error: the mail-mta/postfix package conflicts with another package.
!!!        both can't be installed on the same system together.
!!!        Please use 'emerge --pretend' to determine blockers. 
</pre>

<p>
Ebuilds contain specific fields that inform Portage about its dependencies.
There are two possible dependencies: build dependencies, declared in 
<c>DEPEND</c> and run-time dependencies, declared in <c>RDEPEND</c>. When one of
these dependencies explicitly marks a package or virtual as being <e>not</e>
compatible, it triggers a blockage.
</p>

<p>
To fix a blockage, you can choose to not install the package or unmerge the
conflicting package first. In the given example, you can opt not to install
<c>postfix</c> or to remove <c>ssmtp</c> first.
</p>

<p>
You may also see blocking packages with specific atoms, such as
<b>&lt;</b>media-video/mplayer-bin-1.0_rc1-r2. In this case, updating to a more
recent version of the blocking package would remove the block.
</p>

<p>
It is also possible that two packages that are yet to be installed are blocking
each other. In this rare case, you should find out why you need to install both.
In most cases you can do with one of the packages alone. If not, please file a
bug on <uri link="http://bugs.gentoo.org">Gentoo's bugtracking system</uri>.
</p>

</body>
</subsection>
<subsection id="masked">
<title>Masked Packages</title>
<body>

<pre caption="Portage warning about masked packages">
!!! all ebuilds that could satisfy "bootsplash" have been masked. 
</pre>

<pre caption="Portage warning about masked packages - reason">
!!! possible candidates are:

- gnome-base/gnome-2.8.0_pre1 (masked by: <i>~x86 keyword</i>)
- lm-sensors/lm-sensors-2.8.7 (masked by: <i>-sparc keyword</i>)
- sys-libs/glibc-2.3.4.20040808 (masked by: <i>-* keyword</i>)
- dev-util/cvsd-1.0.2 (masked by: <i>missing keyword</i>)
- games-fps/unreal-tournament-451 (masked by: <i>package.mask</i>)
- sys-libs/glibc-2.3.2-r11 (masked by: <i>profile</i>)
</pre>

<p>
When you want to install a package that isn't available for your system, you
will receive this masking error. You should try installing a different
application that is available for your system or wait until the package is put
available. There is always a reason why a package is masked:
</p>

<ul>
  <li>
    <b>~arch keyword</b> means that the application is not tested sufficiently
    to be put in the stable branch. Wait a few days or weeks and try again.
  </li>
  <li>
    <b>-arch keyword</b> or <b>-* keyword</b> means that the application does 
    not work on your architecture. If you believe the package does work file 
    a bug at our <uri link="http://bugs.gentoo.org">bugzilla</uri> website.
  </li>
  <li>
    <b>missing keyword</b> means that the application has not been tested on
    your architecture yet. Ask the architecture porting team to test the package
    or test it for them and report your findings on our <uri
    link="http://bugs.gentoo.org">bugzilla</uri> website.
  </li>
  <li>
    <b>package.mask</b> means that the package has been found corrupt, unstable
    or worse and has been deliberately marked as do-not-use.
  </li>
  <li>
    <b>profile</b> means that the package has been found not suitable for your
    profile. The application might break your system if you installed it or is
    just not compatible with the profile you use.
  </li>
</ul>

</body>
</subsection>
<subsection id="missingdependencies">
<title>Missing Dependencies</title>
<body>

<pre caption="Portage warning about missing dependency">
emerge: there are no ebuilds to satisfy "&gt;=sys-devel/gcc-3.4.2-r4".

!!! Problem with ebuild sys-devel/gcc-3.4.2-r2
!!! Possibly a DEPEND/*DEPEND problem. 
</pre>

<p>
The application you are trying to install depends on another package that is not
available for your system. Please check <uri
link="http://bugs.gentoo.org">bugzilla</uri> if the issue is known and if not,
please report it. Unless you are mixing branches this should not occur and is
therefore a bug.
</p>

</body>
</subsection>
<subsection id="ambiguousebuild">
<title>Ambiguous Ebuild Name</title>
<body>

<pre caption="Portage warning about ambiguous ebuild names">
!!! The short ebuild name "aterm" is ambiguous.  Please specify
!!! one of the following fully-qualified ebuild names instead:

    dev-libs/aterm
    x11-terms/aterm
</pre>

<p>
The application you want to install has a name that corresponds with more than
one package. You need to supply the category name as well. Portage will inform
you of possible matches to choose from.
</p>

</body>
</subsection>
<subsection id="circulardependencies">
<title>Circular Dependencies</title>
<body>

<pre caption="Portage warning about circular dependencies">
!!! Error: circular dependencies: 

ebuild / net-print/cups-1.1.15-r2 depends on ebuild / app-text/ghostscript-7.05.3-r1
ebuild / app-text/ghostscript-7.05.3-r1 depends on ebuild / net-print/cups-1.1.15-r2 
</pre>

<p>
Two (or more) packages you want to install depend on each other and can
therefore not be installed. This is most likely a bug in the Portage tree.
Please resync after a while and try again. You can also check <uri
link="http://bugs.gentoo.org">bugzilla</uri> if the issue is known and if not,
report it.
</p>

</body>
</subsection>
<subsection id="fetchfailed">
<title>Fetch failed</title>
<body>

<pre caption="Portage warning about fetch failed">
!!! Fetch failed for sys-libs/ncurses-5.4-r5, continuing...
<comment>(...)</comment>
!!! Some fetch errors were encountered.  Please see above for details.
</pre>

<p>
Portage was unable to download the sources for the given application and will
try to continue installing the other applications (if applicable). This failure
can be due to a mirror that has not synchronised correctly or because the ebuild
points to an incorrect location. The server where the sources reside can also be
down for some reason.
</p>

<p>
Retry after one hour to see if the issue still persists.
</p>

</body>
</subsection>
<subsection id="profileprotect">
<title>System Profile Protection</title>
<body>

<pre caption="Portage warning about profile-protected package">
!!! Trying to unmerge package(s) in system profile. 'sys-apps/portage'
!!! This could be damaging to your system.
</pre>

<p>
You have asked to remove a package that is part of your system's core packages.
It is listed in your profile as required and should therefore not be removed
from the system.
</p>

</body>
</subsection>
<subsection id="digesterror">
<title>Digest Verification Failures</title>
<body>

<p>
Sometimes, when you attempt to emerge a package, it will fail with the message:
</p>

<pre caption="Digest verification failure">
&gt;&gt;&gt; checking ebuild checksums
!!! Digest verification failed:
</pre>

<p>
This is a sign that something is wrong with the Portage tree -- often, it is
because a developer may have made a mistake when committing a package to the
tree.
</p>

<p>
When the digest verification fails, do <e>not</e> try to re-digest the package
yourself. Running <c>ebuild foo manifest</c> will not fix the problem; it will
almost certainly make it worse!
</p>

<p>
Instead, wait an hour or two for the tree to settle down. It's likely that the
error was noticed right away, but it can take a little time for the fix to
trickle down the Portage tree. While you're waiting, check <uri
link="http://bugs.gentoo.org">Bugzilla</uri> and see if anyone has reported
the problem yet. If not, go ahead and file a bug for the broken package.
</p>

<p>
Once you see that the bug has been fixed, you may want to re-sync to pick up
the fixed digest.
</p>

<impo>
This does <e>not</e> mean that you can re-sync your tree multiple times! As
stated in the rsync policy (when you run <c>emerge --sync</c>), users who sync
too often will be banned! In fact, it's better to just wait until your next
scheduled sync, so that you don't overload the rsync servers.
</impo>

</body>
</subsection>
</section>
</sections>