Difference between pages "Ebuild Functions" and "Hostname"

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== Ebuild Functions ==
==Introduction==
A hostname is a unique name created to identify a machine on a network. In computer networking, a hostname  is a label that is assigned to a device connected to a computer network and that is used to identify the device in various forms of electronic communication such as the World Wide Web, e-mail or Usenet. Hostnames may be simple names consisting of a single word or phrase, or they may be structured.
==Configuration==
In Funtoo Linux <code>/etc/conf.d/hostname</code> is the only configuration file for setting a hostname. In OpenRC framework <code>/etc/conf.d/foo</code> is the configuration file for a corresponding Init script <code>/etc/init.d/foo</code>.  With the case of hostname, default value in <code>/etc/conf.d/hostname</code> is set to ''localhost'', means when system boots and OpenRC's <code>/etc/init.d/hostname</code> script started a hostname getting only ''localhost'' name.  How it looks?  In your shell promt this will look in following way, an example for root:
<console>
localhost ~ # ##i## Hello :)
</console>
Let's play a bit with a configuration. Open <code>/etc/conf.d/hostname</code> with your favorite editor and set a hostname of your choice.  Below, I will use a real examples  from one of my working test boxes.
<console>
localhost ~ # ##i## nano /etc/conf.d/hostname
</console>
Let's set it to hostname="oleg-stable.host.funtoo.org". Save the file and restart  a hostname service:
<console>
localhost ~ # ##i## service hostname restart
</console>
Now, let's examine our changes, after a restarting a hostname
<console>
oleg-stable ~ # ##i## Hello :)
</console>
== Diving deeper==
Notice, that in above output we seeing a shortened hostname and not a FQDN (Fully Qualified Domain Name). Don't be frustrated. This is  how  default bash promt <code>PS1</code> set. To get nice promts, please, follow http://www.funtoo.org/Prompt_Magic
Another way to test our settings is using a '''hostname''' command. Here we will show only  some of it's features. Let's try to execute '''hostname''' command:
<console>
oleg-stable ~ # ##i## hostname
oleg-stable.host.funtoo.org
</console>
Now we see our fully qualified domain name hostname just how we configured it in <code>/etc/conf.d/hostname</code> in above paragraph. To get a short hostname we need to set '''-s ''' (short) argument to hostname command.
<console>
oleg-stable ~ # ##i## hostname -s
oleg-stable
</console>
Good! Hostname offers more then just displaying a system host name but can also set one. Let's try:
<console>
oleg-stable ~ # ##i## hostname foo.bar.baz
oleg-stable ~ # ##i## hostname
foo.bar.baz
</console>
As you can see, we changed a hostname on-the-fly. This is not recommended way.
{{fancywarning|Please, notice that using '''hostname''' command to configure will work temporary for a current session and will be reverted back to a value set in <code>/etc/conf.d/hostname</code> file with next system restart.}}


Ebuilds provide the ability to define various shell functions that are used to specify various actions relating to building and installing a source or binary package on a user's system. When an ebuild is emerged, the following functions are called, in order:
Now that we got a brief description of a hostname and basic configuration steps, its time to reflect another important case which is directly related to a Funtoo Linux hostname generation, a hosts.


* <tt>pkg_setup</tt> - variable intialization and sanity checks
==Hosts case==
* <tt>src_unpack</tt>
As per man page <code>hosts</code> stands for static table lookup for hostnames and it's configuration file is <code>/etc/hosts</code>. Here is how it looks
* <tt>src_prepare</tt>
{{file|name=/etc/hosts|body=
* <tt>src_configure</tt>
# Auto-generated hostname. Please do not remove this comment.
* <tt>src_compile</tt>
127.0.0.1      oleg-stable.host.funtoo.org oleg-stable localhost localhost.localdomain
* <tt>src_install</tt>
::1            oleg-stable.host.funtoo.org oleg-stable localhost localhost.localdomain
}}
As you can see it has entries from our <code>/etc/conf.d/hostname</code>. As you may have guessed, in Funtoo Linux <code>/etc/hosts</code> file entries are auto-generated, when OpenRC hostname service starts. Previously, it is used to edit <code>/etc/hosts</code> manually. In Funtoo Linux there is no such need.


At this point, the files are ready to be "merged" into the live filesystem. This is when they are copied from the temporary build directory into <tt>/usr</tt>, etc. At this point, the following functions are executed:
What about custom hosts entries? This can be easily configured with 'aliases'. For example you want to have a hosts for your remote router or a computer in home LAN. Let's try to modify <code>/etc/conf.d/hostname</code> with adding following - my remote computer oleg.distant.home has an IP 10.1.1.2:
 
<console>
* <tt>pkg_preinst</tt>
oleg-stable ~ # ##i## echo 'aliases="10.1.12 oleg.distant.home"' >> /etc/conf.d/hostname
* (files are merged)
oleg-stable ~ # ##i## service hostname restart
* <tt>pkg_postinst</tt>
</console>
 
Examine our changes:
=== src_* functions ===
<console>
 
oleg-stable ~ # ##i## cat /etc/hosts
Ebuild functions starting with <tt>src_</tt> are all related to creating the ebuild or package from source code/artifacts, and are defined below:
</console>
 
{{file|name=/etc/hosts|body=
==== src_unpack ====
# Auto-generated hostname. Please do not remove this comment.
 
10.1.1.2        oleg.distant.home
<tt>src_unpack</tt> is intended to be used to unpack the source code/artifacts that will be used by the other <tt>src_*</tt> functions. With EAPI 1 and earlier, it is also used for patching/modifying the source artifacts to prepare them for building, but with EAPI 2 or later the <tt>src_prepare</tt> function should be used for this instead. When <tt>src_unpack</tt> starts, the current working directory is set to <tt>$WORKDIR</tt>, which is the directory within which all source code/artifacts should be expanded. Note that the variable <tt>$A</tt> is set to the names of all the unique source files/artifacts specified in <tt>SRC_URI</tt>, and they will all be available in <tt>$DISTDIR</tt> by the time <tt>src_unpack</tt> starts. Also note that if no <tt>src_unpack</tt> function is specified, <tt>ebuild.sh</tt> will execute the following function for <tt>src_unpack</tt> by default:
127.0.0.1      oleg-stable.host.funtoo.org oleg-stable localhost localhost.localdomain
 
::1            oleg-stable.host.funtoo.org oleg-stable localhost localhost.localdomain
<pre>
}}
src_unpack() {
  unpack ${A}
}
</pre>
 
==== src_prepare ====
 
EAPI 2 and above support the <tt>src_prepare</tt> function, which is intended to be used for applying patches or making other modifications to the source code. When <tt>src_prepare</tt> starts, the current working directory is set to <tt>$S</tt>.
 
==== src_configure ====
 
EAPI 2 and above support the <tt>src_configure</tt> function, which is used to configure the source code prior to compilation. With EAPI 2 and above, the following default <tt>src_configure</tt> is defined if none is specified:
 
<pre>
src_configure() {
if [[ -x ${ECONF_SOURCE:-.}/configure ]] ; then
econf
fi
}
</pre>
 
==== src_compile ====
 
This function defines the steps necessary to compile source code. With EAPI 1 and earlier, this function is also used to configure the source code prior to compilation. However, starting with EAPI 2, the <tt>src_configure</tt> function must be used for configuration steps instead of bundling them inside <tt>src_compile</tt>. In addition, starting with EAPI 2, there is now a default <tt>src_compile</tt> function that will be executed if none is defined in the ebuild:
 
<pre>
src_compile() {
if [ -f Makefile ] || [ -f GNUmakefile ] || [ -f makefile ] ; then
emake || die "emake failed"
fi
}
</pre>
 
==== src_test ====
 
<tt>src_test</tt> is an interesting function - by default, an end-user's Portage does not have tests enabled. But if a user has <tt>test</tt> in <tt>FEATURES</tt>, or <tt>EBUILD_FORCE_TEST</tt> is defined, then <tt>ebuild.sh</tt> will attempt to run a test suite for this ebuild, by executing <tt>make check</tt> or <tt>make test</tt> if these targets are defined in the Makefile; otherwise, no tests will execute. If your Makefile supports <tt>make check</tt> or <tt>make test</tt> but the test suite is broken, then specify <tt>RESTRICT="test"</tt> in your ebuild to disable the test suite.  
 
==== src_install ====
 
<tt>src_install</tt> is used by the ebuild writer to install all to-be-installed files to the <tt>$D</tt> directory, which can be treated like an empty root filesystem, in that <tt>${D}/usr</tt> is the equivalent of the <tt>/usr</tt> directory, etc. When <tt>src_install</tt> runs, the Portage sandbox will be enabled, which will prevent any processes from creating or modifying files outside of the <tt>${D}</tt> filesystem tree, and a sandbox violation will occur (resulting in the termination of the ebuild) if any such sandbox violation should occur. Once <tt>src_install</tt> has perfomed all necessary steps to install all to-be-installed files to <tt>$D</tt>, Portage will take care of merging these files to the filesystem specified by the <tt>$ROOT</tt> environment variable, which defaults to <tt>/</tt> if not set. When Portage merges these files, it will also record information about the installed package to <tt>/var/db/pkg/(cat)/$P</tt>. Typically, a <tt>src_install</tt> function such as this is sufficient for ensuring that all to-be-installed files are installed to <tt>$D</tt>:
 
<pre>
src_install() {
  make DESTDIR="$D" install
}
</pre>
 
=== pkg_* functions ===
 
An ebuild's functions starting with <tt>pkg_*</tt> take a wider view of the package lifecycle, and may be executed very early or very late in the build or package installation process. They are also all executed even if installing a Portage binary package, so are the intended place for defining any global configuration changes that are also required during binary package installation, such as user and group creation. When these functions are executed, the <tt>$ROOT</tt> variable will be defined to point to the target root filesystem to which the package is to be (or has been) installed. All logic inside <tt>pkg_*</tt> functions must function properly even if <tt>$ROOT</tt> is something other than <tt>/</tt>.
 
==== pkg_setup ====
 
The <tt>pkg_setup</tt> function is unusual in that it runs prior to any <tt>src_*</tt> function, and also runs prior to any other <tt>pkg_*</tt> function that runs when a binary package is installed, so it provides a useful place for the ebuild writer to perform any sanity checks, global configuration changes to the system (such as user/group creation) or set any internal global variables that are used by the rest of the ebuild. Using this function for defining global variables that are needed in multiple other functions is a useful way of avoiding duplicate code. You should also look to <tt>pkg_setup</tt> as the ideal place to put any logic that would otherwise linger in the main body of the ebuild, which should be avoided at all costs as it will slow down dependency calculation by Portage. Also remember that Portage can build binary packages, and this function is a good place to execute any steps that are required to run both prior to building an ebuild, and prior to installing a package. Also consider using <tt>pkg_preinst</tt> and <tt>pkg_postinst</tt> for this purpose.
 
==== pkg_pretend ====
 
The <tt>pkg_pretend</tt> function was added with EAPI 3, and it's the opinion of Daniel Robbins that the use of this function should be avoided. This function is especially unusual in that it is intended to be run ''during dependency calculation'', and is intended to provide a polite mechanism to inform the user that a particular ebuild will fail due to a known incompatibility, typically a kernel incompatibility. That way, the user can know during <tt>emerge --pretend</tt> that a merge will fail. While this is useful, extending the dependency engine using <tt>bash</tt> is a very low-performance means to perform these tests. Therefore, The Funtoo core team recommends against using <tt>pkg_pretend</tt>. An extensible dependency engine would be a more appropriate and high-performance way to provide identical functionality.
 
==== pkg_preinst ====
 
The <tt>pkg_preinst</tt> function is called by Portage, prior to merging the to-be-installed files to the target filesystem specified by <tt>$ROOT</tt> environment variable (which defaults to <tt>/</tt>.) Keep in mind that these to-be-installed files were either just compiled and installed to <tt>$D</tt> by <tt>src_install</tt>, or they were just extracted from a <tt>.tbz2</tt> binary package. The <tt>pkg_preinst</tt> function provides an ideal place to perform any "just before install" actions, such as user and group creation or other necessary steps to ensure that the package merges successfully. It also provides a potential place to perform any sanity checks related to installing the package to the target filesystem. If any sanity checks fail, calling <tt>die</tt> from this function will cause the package to not be installed to the target filesystem.
 
==== pkg_postinst ====
 
The <tt>pkg_postinst</tt> function is called by Portage prior to the package being installed to the target filesystem specified by <tt>$ROOT</tt>. This is a good place to perform any post-install configuration actions as well as print any informational messages for the user's benefit related to the package that was just installed.
 
==== pkg_prerm ====
 
The <tt>pkg_prerm</tt> function is called by Portage before an ebuild is removed from the filesystem.
 
==== pkg_postrm ====
 
The <tt>pkg_postrm</tt> function is called by Portage after an ebuild is removed from the filesystem.
 
==== pkg_config ====
 
The <tt>pkg_config</tt> function is called by Portage when the user calls <tt>emerge --config</tt> for the ebuild. The current directory will be set to the current directory of the shell from where <tt>emerge --config</tt> is run.
=== Skipping over a function ===
To skip over a function, create a function that returns a value. For example:
<syntaxhighlight lang="bash">
# Skip src_prepare.
src_prepare() {
    return 0;
}
</syntaxhighlight>
=== Extra pre_ and post_ functions ===
 
Modern versions of Portage also support functions identical to the above functions but with '''pre_''' and '''post_''' at the beginning of the function name. For example, <tt>post_src_configure</tt> will be executed after <tt>src_configure</tt> and before <tt>src_compile</tt>. These additional functions are supported by all EAPIs, provided that the parent function is supported by the EAPI in use. The initial current working directory should be identical to the initial current working directory of the parent function.
 
=== Helper Functions ===
 
==== econf() ====
 
econf() is part of ebuild.sh and is intended to be a wrapper to the <tt>configure</tt> command that is typically used in the <tt>src_configure()</tt> stage. It has a number of behaviors that are important for ebuild writers to understand. Once you understand what <tt>econf()</tt> does, you are free to use it in your ebuilds. Note that the behavior of <tt>econf()</tt> is generally safe for most autoconf-based source archives, but in some cases it may be necessary to avoid using <tt>econf()</tt> to avoid some of its default behaviors.
 
===== Automatically set prefix =====
 
<tt>--prefix=/usr</tt> will be passed to <tt>configure</tt> automatically, unless a <tt>--prefix</tt> argument was specified to <tt>econf()</tt>, in which case, that <tt>--prefix</tt> setting will be used instead.
 
===== Automatically set libdir =====
 
If the <tt>ABI</tt> variable is set (typically done in the profile), then <tt>econf()</tt> will look for a variable named <tt>LIBDIR_$ABI</tt> (ie. <tt>LIBDIR_amd64</tt>). If this variable is set, the value of this variable will be used to set <tt>libdir</tt> to the value of <tt>{prefix}/LIBDIR_$ABI</tt>.
 
===== Automatically set CHOST and CTARGET =====
 
The <tt>--host=$CHOST</tt> argument will be passed to <tt>configure</tt>. <tt>$CHOST</tt> is defined in the system profile. In addition, the <tt>--target=$CTARGET</tt> argument will be passed to <tt>configure</tt> if <tt>$CTARGET</tt> is defined. This is not normally required but is done to make Portage more capable of cross-compiling the ebuild. However, this functionality is not a guarantee that your ebuild will successfully cross-compile, as other changes to the ebuild may be necessary.
 
===== Disable Dependency Tracking (EAPI 4) =====
 
In EAPI 4, the <tt>--disable-dependency-tracking</tt> argument will be passed to <tt>configure</tt> in order to optimize the performance of the configuration process. This option should have no impact other than on the performance of the <tt>configure</tt> script.
 
===== List of arguments =====
 
The following arguments are passed to <tt>configure</tt> and are all overrideable by the user by passing similar options to <tt>econf()</tt>:
 
* <tt>--prefix=/usr</tt>
* <tt>--libdir={prefix}/LIBDIR_$ABI</tt>
* <tt>--host=${CHOST}</tt>
* if CTARGET is defined, then <tt>--target=${CTARGET}</tt>
* <tt>--mandir=/usr/share/man</tt>
* <tt>--infodir=/usr/share/info</tt>
* <tt>--datadir=/usr/share</tt>
* <tt>--sysconfdir=/etc</tt>
* <tt>--localstatedir=/var/lib</tt>
* if EAPI 4+, then <tt>--disable-dependency-tracking</tt>
 
[[Category:Internals]]
[[Category:Portage]]
[[Category:Official Documentation]]

Revision as of 16:06, February 24, 2015

Introduction

A hostname is a unique name created to identify a machine on a network. In computer networking, a hostname is a label that is assigned to a device connected to a computer network and that is used to identify the device in various forms of electronic communication such as the World Wide Web, e-mail or Usenet. Hostnames may be simple names consisting of a single word or phrase, or they may be structured.

Configuration

In Funtoo Linux /etc/conf.d/hostname is the only configuration file for setting a hostname. In OpenRC framework /etc/conf.d/foo is the configuration file for a corresponding Init script /etc/init.d/foo. With the case of hostname, default value in /etc/conf.d/hostname is set to localhost, means when system boots and OpenRC's /etc/init.d/hostname script started a hostname getting only localhost name. How it looks? In your shell promt this will look in following way, an example for root: 

localhost ~ #  Hello :)

Let's play a bit with a configuration. Open /etc/conf.d/hostname with your favorite editor and set a hostname of your choice. Below, I will use a real examples from one of my working test boxes. 

localhost ~ #  nano /etc/conf.d/hostname

Let's set it to hostname="oleg-stable.host.funtoo.org". Save the file and restart a hostname service: 

localhost ~ #  service hostname restart

Now, let's examine our changes, after a restarting a hostname 

oleg-stable ~ #  Hello :)

Diving deeper

Notice, that in above output we seeing a shortened hostname and not a FQDN (Fully Qualified Domain Name). Don't be frustrated. This is how default bash promt PS1 set. To get nice promts, please, follow http://www.funtoo.org/Prompt_Magic Another way to test our settings is using a hostname command. Here we will show only some of it's features. Let's try to execute hostname command: 

oleg-stable ~ #  hostname
oleg-stable.host.funtoo.org

Now we see our fully qualified domain name hostname just how we configured it in /etc/conf.d/hostname in above paragraph. To get a short hostname we need to set -s (short) argument to hostname command. 

oleg-stable ~ #  hostname -s
oleg-stable

Good! Hostname offers more then just displaying a system host name but can also set one. Let's try: 

oleg-stable ~ #  hostname foo.bar.baz
oleg-stable ~ #  hostname 
foo.bar.baz

As you can see, we changed a hostname on-the-fly. This is not recommended way.

   Warning

Please, notice that using hostname command to configure will work temporary for a current session and will be reverted back to a value set in /etc/conf.d/hostname file with next system restart.

Now that we got a brief description of a hostname and basic configuration steps, its time to reflect another important case which is directly related to a Funtoo Linux hostname generation, a hosts.

Hosts case

As per man page hosts stands for static table lookup for hostnames and it's configuration file is /etc/hosts. Here is how it looks

   /etc/hosts 
# Auto-generated hostname. Please do not remove this comment.
127.0.0.1       oleg-stable.host.funtoo.org oleg-stable localhost localhost.localdomain
::1             oleg-stable.host.funtoo.org oleg-stable localhost localhost.localdomain

As you can see it has entries from our /etc/conf.d/hostname. As you may have guessed, in Funtoo Linux /etc/hosts file entries are auto-generated, when OpenRC hostname service starts. Previously, it is used to edit /etc/hosts manually. In Funtoo Linux there is no such need.

What about custom hosts entries? This can be easily configured with 'aliases'. For example you want to have a hosts for your remote router or a computer in home LAN. Let's try to modify /etc/conf.d/hostname with adding following - my remote computer oleg.distant.home has an IP 10.1.1.2: 

oleg-stable ~ #  echo 'aliases="10.1.12 oleg.distant.home"' >> /etc/conf.d/hostname
oleg-stable ~ #  service hostname restart

Examine our changes:

oleg-stable ~ #  cat /etc/hosts
   /etc/hosts 
# Auto-generated hostname. Please do not remove this comment.
10.1.1.2        oleg.distant.home
127.0.0.1       oleg-stable.host.funtoo.org oleg-stable localhost localhost.localdomain
::1             oleg-stable.host.funtoo.org oleg-stable localhost localhost.localdomain
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