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785 lines
35 KiB
XML
785 lines
35 KiB
XML
<?xml version="1.0" encoding="ISO-8859-1"?>
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<!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
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<!ENTITY % general-entities SYSTEM "../../general.ent">
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%general-entities;
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]>
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<sect1 id="unpacking">
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<?dbhtml filename="notes-on-building.html"?>
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<sect1info>
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<date>$Date$</date>
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</sect1info>
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<title>Notes on Building Software</title>
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<para>Those people who have built an LFS system may be aware
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of the general principles of downloading and unpacking software. Some
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of that information is repeated here for those new to building
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their own software.</para>
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<para>Each set of installation instructions contains a URL from which you
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can download the package. The patches; however, are stored on the LFS
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servers and are available via HTTP. These are referenced as needed in the
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installation instructions.</para>
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<para>While you can keep the source files anywhere you like, we assume that
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you have unpacked the package and changed into the directory created by the
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unpacking process (the 'build' directory). We also assume you have
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uncompressed any required patches and they are in the directory immediately
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above the 'build' directory.</para>
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<para>We can not emphasize strongly enough that you should start from a
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<emphasis>clean source tree</emphasis> each time. This means that if
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you have had an error during configuration or compilation, it's usually
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best to delete the source tree and
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re-unpack it <emphasis>before</emphasis> trying again. This obviously
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doesn't apply if you're an advanced user used to hacking
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<filename>Makefile</filename>s and C code, but if in doubt, start from a
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clean tree.</para>
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<sect2>
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<title>Building Software as an Unprivileged (non-root) User</title>
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<para>The golden rule of Unix System Administration is to use your
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superpowers only when necessary. Hence, BLFS recommends that you
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build software as an unprivileged user and only become the
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<systemitem class='username'>root</systemitem> user when installing the
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software. This philosophy is followed in all the packages in this book.
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Unless otherwise specified, all instructions should be executed as an
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unprivileged user. The book will advise you on instructions that need
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<systemitem class='username'>root</systemitem> privileges.</para>
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</sect2>
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<sect2>
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<title>Unpacking the Software</title>
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<para>If a file is in <filename class='extension'>.tar</filename> format
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and compressed, it is unpacked by running one of the following
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commands:</para>
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<screen><userinput>tar -xvf filename.tar.gz
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tar -xvf filename.tgz
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tar -xvf filename.tar.Z
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tar -xvf filename.tar.bz2</userinput></screen>
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<note>
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<para>You may omit using the <option>v</option> parameter in the commands
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shown above and below if you wish to suppress the verbose listing of all
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the files in the archive as they are extracted. This can help speed up the
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extraction as well as make any errors produced during the extraction
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more obvious to you.</para>
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</note>
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<para>You can also use a slightly different method:</para>
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<screen><userinput>bzcat filename.tar.bz2 | tar -xv</userinput></screen>
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<para>Finally, you sometimes need to be able to unpack patches which are
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generally not in <filename class='extension'>.tar</filename> format. The
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best way to do this is to copy the patch file to the parent of the 'build'
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directory and then run one of the following commands depending on whether
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the file is a <filename class='extension'>.gz</filename> or <filename
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class='extension'>.bz2</filename> file:</para>
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<screen><userinput>gunzip -v patchname.gz
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bunzip2 -v patchname.bz2</userinput></screen>
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</sect2>
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<sect2>
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<title>Verifying File Integrity Using 'md5sum'</title>
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<para>Generally, to verify that the downloaded file is genuine and complete,
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many package maintainers also distribute md5sums of the files. To verify the
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md5sum of the downloaded files, download both the file and the
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corresponding md5sum file to the same directory (preferably from different
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on-line locations), and (assuming <filename>file.md5sum</filename> is the
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md5sum file downloaded) run the following command:</para>
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<screen><userinput>md5sum -c file.md5sum</userinput></screen>
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<para>If there are any errors, they will be reported. Note that the BLFS
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book includes md5sums for all the source files also. To use the BLFS
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supplied md5sums, you can create a <filename>file.md5sum</filename> (place
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the md5sum data and the exact name of the downloaded file on the same
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line of a file, separated by white space) and run the command shown above.
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Alternately, simply run the command shown below and compare the output
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to the md5sum data shown in the BLFS book.</para>
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<screen><userinput>md5sum <replaceable><name_of_downloaded_file></replaceable></userinput></screen>
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</sect2>
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<sect2>
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<title>Creating Log Files During Installation</title>
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<para>For larger packages, it is convenient to create log files instead of
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staring at the screen hoping to catch a particular error or warning. Log
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files are also useful for debugging and keeping records. The following
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command allows you to create an installation log. Replace
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<replaceable><command></replaceable> with the command you intend to execute.</para>
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<screen><userinput>( <replaceable><command></replaceable> 2>&1 | tee compile.log && exit $PIPESTATUS )</userinput></screen>
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<para><option>2>&1</option> redirects error messages to the same
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location as standard output. The <command>tee</command> command allows
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viewing of the output while logging the results to a file. The parentheses
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around the command run the entire command in a subshell and finally the
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<command>exit $PIPESTATUS</command> command ensures the result of the
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<replaceable><command></replaceable> is returned as the result and not the
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result of the <command>tee</command> command.</para>
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</sect2>
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<sect2 id="parallel-builds" xreflabel="Using Multiple Processors">
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<title>Using Multiple Processors</title>
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<para>For many modern systems with multiple processors (or cores) the
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compilation time for a package can be reduced by performing a "parallel
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make" by either setting an environment variable or telling the make program
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how many processors are available. For instance, a Core2Duo can support two
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simultaneous processes with: </para>
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<screen><userinput>export MAKEFLAGS='-j2'</userinput></screen>
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<para>or just building with:</para>
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<screen><userinput>make -j2</userinput></screen>
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<para>Generally the number of processes should not exceed the number of
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cores supported by the CPU. To list the processors on your
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system, issue: <userinput>grep processor /proc/cpuinfo</userinput>.
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</para>
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<para>In some cases, using multiple processors may result in a 'race'
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condition where the success of the build depends on the order of the
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commands run by the <command>make</command> program. For instance, if an
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executable needs File A and File B, attempting to link the program before
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one of the dependent components is available will result in a failure.
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This condition usually arises because the upstream developer has not
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properly designated all the prerequisites needed to accomplish a step in the
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Makefile.</para>
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<para>If this occurs, the best way to proceed is to drop back to a
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single processor build. Adding '-j1' to a make command will override
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the similar setting in the MAKEFLAGS environment variable.</para>
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<note><para>When running the package tests or the install portion of the
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package build process, we do not recommend using an option greater than
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'-j1' unless specified otherwise. The installation procedures or checks
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have not been validated using parallel procedures and may fail with issues
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that are difficult to debug.</para></note>
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</sect2>
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<sect2 id="automating-builds" xreflabel="Automated Building Procedures">
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<title>Automated Building Procedures</title>
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<para>There are times when automating the building of a package can come in
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handy. Everyone has their own reasons for wanting to automate building,
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and everyone goes about it in their own way. Creating
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<filename>Makefile</filename>s, <application>Bash</application> scripts,
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<application>Perl</application> scripts or simply a list of commands used
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to cut and paste are just some of the methods you can use to automate
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building BLFS packages. Detailing how and providing examples of the many
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ways you can automate the building of packages is beyond the scope of this
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section. This section will expose you to using file redirection and the
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<command>yes</command> command to help provide ideas on how to automate
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your builds.</para>
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<bridgehead renderas="sect3">File Redirection to Automate Input</bridgehead>
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<para>You will find times throughout your BLFS journey when you will come
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across a package that has a command prompting you for information. This
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information might be configuration details, a directory path, or a response
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to a license agreement. This can present a challenge to automate the
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building of that package. Occasionally, you will be prompted for different
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information in a series of questions. One method to automate this type of
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scenario requires putting the desired responses in a file and using
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redirection so that the program uses the data in the file as the answers to
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the questions.</para>
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<para>Building the <application>CUPS</application> package is a good
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example of how redirecting a file as input to prompts can help you automate
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the build. If you run the test suite, you are asked to respond to a series
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of questions regarding the type of test to run and if you have any
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auxiliary programs the test can use. You can create a file with your
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responses, one response per line, and use a command similar to the
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one shown below to automate running the test suite:</para>
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<screen><userinput>make check < ../cups-1.1.23-testsuite_parms</userinput></screen>
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<para>This effectively makes the test suite use the responses in the file
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as the input to the questions. Occasionally you may end up doing a bit of
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trial and error determining the exact format of your input file for some
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things, but once figured out and documented you can use this to automate
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building the package.</para>
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<bridgehead renderas="sect3">Using <command>yes</command> to Automate
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Input</bridgehead>
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<para>Sometimes you will only need to provide one response, or provide the
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same response to many prompts. For these instances, the
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<command>yes</command> command works really well. The
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<command>yes</command> command can be used to provide a response (the same
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one) to one or more instances of questions. It can be used to simulate
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pressing just the <keycap>Enter</keycap> key, entering the
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<keycap>Y</keycap> key or entering a string of text. Perhaps the easiest
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way to show its use is in an example.</para>
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<para>First, create a short <application>Bash</application> script by
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entering the following commands:</para>
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<screen><userinput>cat > blfs-yes-test1 << "EOF"
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<literal>#!/bin/bash
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echo -n -e "\n\nPlease type something (or nothing) and press Enter ---> "
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read A_STRING
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if test "$A_STRING" = ""; then A_STRING="Just the Enter key was pressed"
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else A_STRING="You entered '$A_STRING'"
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fi
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echo -e "\n\n$A_STRING\n\n"</literal>
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EOF
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chmod 755 blfs-yes-test1</userinput></screen>
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<para>Now run the script by issuing <command>./blfs-yes-test1</command> from
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the command line. It will wait for a response, which can be anything (or
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nothing) followed by the <keycap>Enter</keycap> key. After entering
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something, the result will be echoed to the screen. Now use the
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<command>yes</command> command to automate the entering of a
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response:</para>
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<screen><userinput>yes | ./blfs-yes-test1</userinput></screen>
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<para>Notice that piping <command>yes</command> by itself to the script
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results in <keycap>y</keycap> being passed to the script. Now try it with a
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string of text:</para>
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<screen><userinput>yes 'This is some text' | ./blfs-yes-test1</userinput></screen>
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<para>The exact string was used as the response to the script. Finally,
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try it using an empty (null) string:</para>
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<screen><userinput>yes '' | ./blfs-yes-test1</userinput></screen>
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<para>Notice this results in passing just the press of the
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<keycap>Enter</keycap> key to the script. This is useful for times when the
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default answer to the prompt is sufficient. This syntax is used in the
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<xref linkend="net-tools-automate-example"/> instructions to accept all the
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defaults to the many prompts during the configuration step. You may now
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remove the test script, if desired.</para>
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<bridgehead renderas="sect3">File Redirection to Automate Output</bridgehead>
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<para>In order to automate the building of some packages, especially those
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that require you to read a license agreement one page at a time, requires
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using a method that avoids having to press a key to display each page.
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Redirecting the output to a file can be used in these instances to assist
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with the automation. The previous section on this page touched on creating
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log files of the build output. The redirection method shown there used the
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<command>tee</command> command to redirect output to a file while also
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displaying the output to the screen. Here, the output will only be sent to
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a file.</para>
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<para>Again, the easiest way to demonstrate the technique is to show an
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example. First, issue the command:</para>
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<screen><userinput>ls -l /usr/bin | more</userinput></screen>
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<para>Of course, you'll be required to view the output one page at a time
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because the <command>more</command> filter was used. Now try the same
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command, but this time redirect the output to a file. The special file
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<filename>/dev/null</filename> can be used instead of the filename shown,
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but you will have no log file to examine:</para>
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<screen><userinput>ls -l /usr/bin | more > redirect_test.log 2>&1</userinput></screen>
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<para>Notice that this time the command immediately returned to the shell
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prompt without having to page through the output. You may now remove the
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log file.</para>
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<para>The last example will use the <command>yes</command> command in
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combination with output redirection to bypass having to page through the
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output and then provide a <keycap>y</keycap> to a prompt. This technique
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could be used in instances when otherwise you would have to page through
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the output of a file (such as a license agreement) and then answer the
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question of <quote>do you accept the above?</quote>. For this example,
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another short <application>Bash</application> script is required:</para>
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<screen><userinput>cat > blfs-yes-test2 << "EOF"
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<literal>#!/bin/bash
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ls -l /usr/bin | more
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echo -n -e "\n\nDid you enjoy reading this? (y,n) "
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read A_STRING
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if test "$A_STRING" = "y"; then A_STRING="You entered the 'y' key"
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else A_STRING="You did NOT enter the 'y' key"
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fi
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echo -e "\n\n$A_STRING\n\n"</literal>
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EOF
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chmod 755 blfs-yes-test2</userinput></screen>
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<para>This script can be used to simulate a program that requires you to
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read a license agreement, then respond appropriately to accept the
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agreement before the program will install anything. First, run the script
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without any automation techniques by issuing
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<command>./blfs-yes-test2</command>.</para>
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<para>Now issue the following command which uses two automation techniques,
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making it suitable for use in an automated build script:</para>
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<screen><userinput>yes | ./blfs-yes-test2 > blfs-yes-test2.log 2>&1</userinput></screen>
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<para>If desired, issue <command>tail blfs-yes-test2.log</command> to see
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the end of the paged output, and confirmation that <keycap>y</keycap> was
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passed through to the script. Once satisfied that it works as it should,
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you may remove the script and log file.</para>
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<para>Finally, keep in mind that there are many ways to automate and/or
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script the build commands. There is not a single <quote>correct</quote> way
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to do it. Your imagination is the only limit.</para>
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</sect2>
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<sect2>
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<title>Dependencies</title>
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<para>For each package described, BLFS lists the known dependencies.
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These are listed under several headings, whose meaning is as follows:</para>
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<itemizedlist>
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<listitem>
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<para><emphasis>Required</emphasis> means that the target package
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cannot be correctly built without the dependency having first been
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installed.</para>
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</listitem>
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<listitem>
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<para><emphasis>Recommended</emphasis> means that BLFS strongly
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suggests this package is installed first for a clean and trouble-free
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build, that won't have issues either during the build process, or at
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run-time. The instructions in the book assume these packages are
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installed. Some changes or workarounds may be required if these
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packages are not installed.</para>
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</listitem>
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<listitem>
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<para><emphasis>Optional</emphasis> means that this package might be
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installed for added functionality. Often BLFS will describe the
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dependency to explain the added functionality that will result.</para>
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</listitem>
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</itemizedlist>
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</sect2>
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<sect2 id="package_updates">
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<title>Using the Most Current Package Sources</title>
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<para>On occasion you may run into a situation in the book when a package
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will not build or work properly. Though the Editors attempt to ensure
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that every package in the book builds and works properly, sometimes a
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package has been overlooked or was not tested with this particular version
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of BLFS.</para>
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<para>If you discover that a package will not build or work properly, you
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should see if there is a more current version of the package. Typically
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this means you go to the maintainer's web site and download the most current
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tarball and attempt to build the package. If you cannot determine the
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maintainer's web site by looking at the download URLs, use Google and query
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the package's name. For example, in the Google search bar type:
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'package_name download' (omit the quotes) or something similar. Sometimes
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typing: 'package_name home page' will result in you finding the
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maintainer's web site.</para>
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</sect2>
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<sect2 id="stripping">
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<title>Stripping One More Time</title>
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<para>
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In LFS, stripping of debugging symbols was discussed a couple of
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times. When building BLFS packages, there are generally no special
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instructions that discuss stripping again. It is probably not a good
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idea to strip an executable or a library while it is in use, so exiting
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any windowing environment is a good idea. Then you can do:
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</para>
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<screen><userinput>find /{,usr/}{bin,lib,sbin} \
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-type f \( -name \*.so* -a ! -name \*dbg \) \
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-exec strip --strip-unneeded {} \;</userinput></screen>
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<para>
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If you install programs in other directories such as <filename
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class="directory">/opt</filename> or <filename
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class="directory">/usr/local</filename>, you may want to strip the files
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there too.
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</para>
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<para>
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For more information on stripping, see <ulink
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url="http://www.technovelty.org/linux/stripping-shared-libraries.html"/>.
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</para>
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</sect2>
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<!--
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<sect2 id="libtool">
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<title>Libtool files</title>
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<para>
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One of the side effects of packages that use Autotools, including
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libtool, is that they create many files with an .la extension. These
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files are not needed in an LFS environment. If there are conflicts with
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pkgconfig entries, they can actually prevent successful builds. You
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may want to consider removing these files periodically:
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</para>
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<screen><userinput>find /lib /usr/lib -not -path "*Image*" -a -name \*.la -delete</userinput></screen>
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<para>
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The above command removes all .la files with the exception of those that
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have <quote>Image</quote> or <quote>openldap</quote> as a part of the
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path. These .la files are used by the ImageMagick and openldap programs,
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|
respectively. There may be other exceptions by packages not in BLFS.
|
|
</para>
|
|
|
|
</sect2>
|
|
-->
|
|
<sect2 id="buildsystems">
|
|
<title>Working with different build systems</title>
|
|
|
|
<para>
|
|
There are now three different build systems in common use for
|
|
converting C or C++ source code into compiled programs or
|
|
libraries and their details (particularly, finding out about available
|
|
options and their default values) differ. It may be easiest to understand
|
|
the issues caused by some choices (typically slow execution or
|
|
unexpected use of, or omission of, optimizatons) by starting with
|
|
the CFLAGS and CXXFLAGS environment variables. There are also some
|
|
programs which use rust.
|
|
</para>
|
|
|
|
<para>
|
|
Most LFS and BLFS builders are probably aware of the basics of CFLAGS
|
|
and CXXFLAGS for altering how a program is compiled. Typically, some
|
|
form of optimization is used by upstream developers (-O2 or -O3),
|
|
sometimes with the creation of debug symbols (-g), as defaults.
|
|
</para>
|
|
|
|
<para>
|
|
If there are contradictory flags (e.g. multiple different -O values),
|
|
the <emphasis>last</emphasis> value will be used. Sometimes this means
|
|
that flags specified in environment variables will be picked up before
|
|
values hardcoded in the Makefile, and therefore ignored. For example,
|
|
where a user specifies '-O2' and that is followed by '-O3' the build will
|
|
use '-O3'.
|
|
</para>
|
|
|
|
<para>
|
|
There are various other things which can be passed in CFLAGS or
|
|
CXXFLAGS, such as forcing compilation for a specific microarchitecture
|
|
(e.g. -march=amdfam10, -march=native) or specifying a specific standard
|
|
for C or C++ (-std=c++17 for example). But one thing which has now come
|
|
to light is that programmers might include debug assertions in their
|
|
code, expecting them to be disabled in releases by using -DNDEBUG.
|
|
Specifically, if <xref linkend="mesa"/> is built with these assertions
|
|
enabled, some activities such as loading levels of games can take
|
|
extremely long times, even on high-class video cards.
|
|
</para>
|
|
|
|
<bridgehead renderas="sect3" id="autotools-info">Autotools with Make</bridgehead>
|
|
|
|
<para>
|
|
This combination is often described as 'CMMI' (configure, make, make
|
|
install) and is used here to also cover the few packages which have a
|
|
configure script that is not generated by autotools.
|
|
</para>
|
|
|
|
<para>
|
|
Sometimes running <command>./configure --help</command> will produce
|
|
useful options about switches which might be used. At other times,
|
|
after looking at the output from configure you may need to look
|
|
at the details of the script to find out what it was actually searching
|
|
for.
|
|
</para>
|
|
|
|
<para>
|
|
Many configure scripts will pick up any CFLAGS or CXXFLAGS from the
|
|
environment, but CMMI packages vary about how these will be mixed with
|
|
any flags which would otherwise be used (<emphasis>variously</emphasis>:
|
|
ignored, used to replace the programmer's suggestion, used before the
|
|
programmer's suggestion, or used after the programmer's suggestion).
|
|
</para>
|
|
|
|
<para>
|
|
In most CMMI packages, running 'make' will list each command and run
|
|
it, interspersed with any warnings. But some packages try to be 'silent'
|
|
and only show which file they are compiling or linking instead of showing
|
|
the command line. If you need to inspect the command, either because of
|
|
an error, or just to see what options and flags are being used, adding
|
|
'V=1' to the make invocation may help.
|
|
</para>
|
|
|
|
<bridgehead renderas="sect3" id="cmake-info">CMake</bridgehead>
|
|
|
|
<para>
|
|
CMake works in a very different way, and it has two backends which can
|
|
be used on BLFS: 'make' and 'ninja'. The default backend is make, but
|
|
ninja can be faster on large packages with multiple processors. To
|
|
use ninja, specify '-G Ninja' in the cmake command. However, there are
|
|
some packages which create fatal errors in their ninja files but build
|
|
successfully using the default of Unix Makefiles.
|
|
</para>
|
|
|
|
<para>
|
|
The hardest part of using CMake is knowing what options you might wish
|
|
to specify. The only way to get a list of what the package knows about
|
|
is to run <command>cmake -LAH</command> and look at the output for that
|
|
default configuration.
|
|
</para>
|
|
|
|
<para>
|
|
Perhaps the most-important thing about CMake is that it has a variety
|
|
of CMAKE_BUILD_TYPE values, and these affect the flags. The default
|
|
is that this is not set and no flags are generated. Any CFLAGS or
|
|
CXXFLAGS in the environment will be used. If the programmer has coded
|
|
any debug assertions, those will be enabled unless -DNDEBUG is used.
|
|
The following CMAKE_BUILD_TYPE values will generate the flags shown,
|
|
and these will come <emphasis>after</emphasis> any flags in the
|
|
environment and therefore take precedence.
|
|
</para>
|
|
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>Debug : '-g'</para>
|
|
</listitem>
|
|
<listitem>
|
|
<para>Release : '-O3 -DNDEBUG'</para>
|
|
</listitem>
|
|
<listitem>
|
|
<para>RelWithDebInfo : '-O2 -g -DNDEBUG'</para>
|
|
</listitem>
|
|
<listitem>
|
|
<para>MinSizeRel : '-Os -DNDEBUG'</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
|
|
<para>
|
|
CMake tries to produce quiet builds. To see the details of the commands
|
|
which are being run, use 'make VERBOSE=1' or 'ninja -v'.
|
|
</para>
|
|
|
|
<bridgehead renderas="sect3" id="meson-info">Meson</bridgehead>
|
|
|
|
<para>
|
|
Meson has some similarities to CMake, but many differences. To get
|
|
details of the defines that you may wish to change you can look at
|
|
<filename>meson_options.txt</filename> which is usually in the
|
|
top-level directory.
|
|
</para>
|
|
|
|
<para>
|
|
If you have already configured the package by running
|
|
<command>meson</command> and now wish to change one or more settings,
|
|
you can either remove the build directory, recreate it, and use the
|
|
altered options, or within the build directory run <command>meson
|
|
configure</command>, e.g. to set an option:
|
|
</para>
|
|
|
|
<screen><userinput>meson configure -D<some_option>=true</userinput></screen>
|
|
|
|
<para>
|
|
If you do that, the file <filename>meson-private/cmd_line.txt</filename>
|
|
will show the <emphasis>last</emphasis> commands which were used.
|
|
</para>
|
|
|
|
<para>
|
|
Meson provides the following buildtype values, and the flags they enable
|
|
come <emphasis>after</emphasis> any flags supplied in the environment and
|
|
therefore take precedence.
|
|
</para>
|
|
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>plain : no added flags. This is for distributors to supply their
|
|
own CLFAGS, CXXFLAGS and LDFLAGS. There is no obvious reason to use
|
|
this in BLFS.</para>
|
|
</listitem>
|
|
<listitem>
|
|
<para>debug : '-g'</para>
|
|
</listitem>
|
|
<listitem>
|
|
<para>debugoptimized : '-O2 -g' - this is the default if nothing is
|
|
specified, it leaves assertions enabled.</para>
|
|
</listitem>
|
|
<listitem>
|
|
<para>release : '-O3 -DNDEBUG' (but occasionally a package will force
|
|
-O2 here)</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
|
|
<para>
|
|
Although the 'release' buildtype is described as enabling -DNDEBUG, and all
|
|
CMake Release builds pass that, it has so far only been observed (in
|
|
verbose builds) for <xref linkend="mesa"/>. That suggests that it might
|
|
only be used when there are debug assertions present.
|
|
</para>
|
|
|
|
<para>
|
|
The -DNDEBUG flag can also be provided by passing
|
|
<command>-Db_ndebug=true</command>.
|
|
</para>
|
|
|
|
<para>
|
|
To see the details of the commands which are being run in a package using
|
|
meson, use 'ninja -v'.
|
|
</para>
|
|
|
|
<bridgehead renderas="sect3" id="rust-info">Rustc and Cargo</bridgehead>
|
|
|
|
<para>
|
|
Most released rustc programs are provided as crates (source tarballs)
|
|
which will query a server to check current versions of dependencies
|
|
and then download them as necessary. These packages are built using
|
|
<command>cargo --release</command>. In theory, you can manipulate the
|
|
RUSTFLAGS to change the optimize-level (default is 3, like -O3, e.g.
|
|
<literal>-Copt-level=3</literal>) or to force it to build for the
|
|
machine it is being compiled on, using
|
|
<literal>-Ctarget-cpu=native</literal> but in practice this seems to
|
|
make no significant difference.
|
|
</para>
|
|
|
|
<para>
|
|
If you find an interesting rustc program which is only provided as
|
|
unpackaged source, you should at least specify
|
|
<literal>RUSTFLAGS=-Copt-level=2</literal> otherwise it will do an
|
|
unoptimized compile with debug info and run <emphasis>much</emphasis>
|
|
slower.
|
|
</para>
|
|
|
|
<para>
|
|
The rust developers seem to assume that everyone will compile on a
|
|
machine dedicated to producing builds, so by default all CPUs are used.
|
|
This can often be worked around, either by exporting
|
|
CARGO_BUILD_JOBS=<N> or passing --jobs <N> to cargo. For
|
|
compiling rustc itself, specifying --jobs <N> on invocations of
|
|
x.py (together with the <envar>CARGO_BUILD_JOBS</envar> environment
|
|
variable, which looks like a "belt and braces" approach but seems to be
|
|
necessary) mostly works. The exception is running the tests when building
|
|
rustc, some of them will nevertheless use all online CPUs, at least as of
|
|
rustc-1.42.0.
|
|
</para>
|
|
|
|
</sect2>
|
|
|
|
<sect2 id="optimizations">
|
|
<title>Optimizing the build</title>
|
|
|
|
<para>
|
|
Many people will prefer to optimize compiles as they see fit, by providing
|
|
CFLAGS or CXXFLAGS. For an introduction to the options available with gcc
|
|
and g++ see <ulink
|
|
url="https://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html"/> and <ulink
|
|
url="https://gcc.gnu.org/onlinedocs/gcc/Instrumentation-Options.html"/>
|
|
and <command>info gcc</command>.
|
|
|
|
</para>
|
|
|
|
<para>
|
|
Some packages default to '-O2 -g', others to '-O3 -g', and if CFLAGS or
|
|
CXXFLAGS are supplied they might be added to the package's defaults,
|
|
replace the package's defaults, or even be ignored. There are details
|
|
on some desktop packages which were mostly current in April 2019 at
|
|
<ulink url="https://www.linuxfromscratch.org/~ken/tuning/"/> - in
|
|
particular, README.txt, tuning-1-packages-and-notes.txt, and
|
|
tuning-notes-2B.txt. The particular thing to remember is that if you
|
|
want to try some of the more interesting flags you may need to force
|
|
verbose builds to confirm what is being used.
|
|
</para>
|
|
|
|
<para>
|
|
Clearly, if you are optimizing your own program you can spend time to
|
|
profile it and perhaps recode some of it if it is too slow. But for
|
|
building a whole system that approach is impractical. In general,
|
|
-O3 usually produces faster programs than -O2. Specifying
|
|
-march=native is also beneficial, but means that you cannot move the
|
|
binaries to an incompatible machine - this can also apply to newer
|
|
machines, not just to older machines. For example programs compiled for
|
|
'amdfam10' run on old Phenoms, Kaveris, and Ryzens : but programs
|
|
compiled for a Kaveri will not run on a Ryzen because certain op-codes
|
|
are not present. Similarly, if you build for a Haswell not everything
|
|
will run on a SandyBridge.
|
|
</para>
|
|
|
|
<para>
|
|
There are also various other options which some people claim are
|
|
beneficial. At worst, you get to recompile and test, and then
|
|
discover that in your usage the options do not provide a benefit.
|
|
</para>
|
|
|
|
<para>
|
|
If building Perl or Python modules, or Qt packages which use qmake,
|
|
in general the CFLAGS and CXXFLAGS used are those which were used by
|
|
those 'parent' packages.
|
|
</para>
|
|
|
|
</sect2>
|
|
|
|
<sect2 id="hardening">
|
|
<title>Options for hardening the build</title>
|
|
|
|
<para>
|
|
Even on desktop systems, there are still a lot of exploitable
|
|
vulnerabilities. For many of these, the attack comes via javascript
|
|
in a browser. Often, a series of vulnerabilities are used to gain
|
|
access to data (or sometimes to pwn, i.e. own, the machine and
|
|
install rootkits). Most commercial distros will apply various
|
|
hardening measures.
|
|
</para>
|
|
|
|
<para>
|
|
For hardening options which are reasonably cheap, there is some
|
|
discussion in the 'tuning' link above (occasionally, one or more
|
|
of these options might be inappropriate for a package). These
|
|
options are -D_FORTIFY_SOURCE=2, -fstack-protector=strong, and
|
|
(for C++) -D_GLIBCXX_ASSERTIONS. On modern machines these should
|
|
only have a little impact on how fast things run, and often they
|
|
will not be noticeable.
|
|
</para>
|
|
|
|
<para>
|
|
In the past, there was Hardened LFS where gcc (a much older version)
|
|
was forced to use hardening (with options to turn some of it off on a
|
|
per-package basis. What is being covered here is different - first you
|
|
have to make sure that the package is indeed using your added flags and
|
|
not over-riding them.
|
|
</para>
|
|
|
|
<para>
|
|
The main distros use much more, such as RELRO (Relocation Read Only)
|
|
and perhaps -fstack-clash-protection. You may also encounter the
|
|
so-called 'userspace retpoline' (-mindirect-branch=thunk etc.) which
|
|
is the equivalent of the spectre mitigations applied to the linux
|
|
kernel in late 2018). The kernel mitigations caused a lot of complaints
|
|
about lost performance, if you have a production server you might wish
|
|
to consider testing that, along with the other available options, to
|
|
see if performance is still sufficient.
|
|
</para>
|
|
|
|
<para>
|
|
Whilst gcc has many hardening options, clang/LLVM's strengths lie
|
|
elsewhere. Some options which gcc provides are said to be less effective
|
|
in clang/LLVM.
|
|
</para>
|
|
|
|
</sect2>
|
|
|
|
</sect1>
|