1 | <?xml version="1.0" encoding="ISO-8859-1"?>
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2 | <!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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3 | "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
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4 | <!ENTITY % general-entities SYSTEM "../../general.ent">
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5 | %general-entities;
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6 | ]>
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7 |
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8 | <sect1 id="unpacking">
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9 | <?dbhtml filename="notes-on-building.html"?>
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10 |
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11 | <sect1info>
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12 | <date>$Date$</date>
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13 | </sect1info>
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14 |
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15 | <title>Notes on Building Software</title>
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16 |
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17 | <para>Those people who have built an LFS system may be aware
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18 | of the general principles of downloading and unpacking software. Some
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19 | of that information is repeated here for those new to building
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20 | their own software.</para>
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21 |
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22 | <para>Each set of installation instructions contains a URL from which you
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23 | can download the package. The patches; however, are stored on the LFS
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24 | servers and are available via HTTP. These are referenced as needed in the
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25 | installation instructions.</para>
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26 |
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27 | <para>While you can keep the source files anywhere you like, we assume that
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28 | you have unpacked the package and changed into the directory created by the
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29 | unpacking process (the 'build' directory). We also assume you have
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30 | uncompressed any required patches and they are in the directory immediately
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31 | above the 'build' directory.</para>
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32 |
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33 | <para>We can not emphasize strongly enough that you should start from a
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34 | <emphasis>clean source tree</emphasis> each time. This means that if
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35 | you have had an error during configuration or compilation, it's usually
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36 | best to delete the source tree and
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37 | re-unpack it <emphasis>before</emphasis> trying again. This obviously
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38 | doesn't apply if you're an advanced user used to hacking
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39 | <filename>Makefile</filename>s and C code, but if in doubt, start from a
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40 | clean tree.</para>
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41 |
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42 | <sect2>
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43 | <title>Building Software as an Unprivileged (non-root) User</title>
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44 |
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45 | <para>The golden rule of Unix System Administration is to use your
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46 | superpowers only when necessary. Hence, BLFS recommends that you
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47 | build software as an unprivileged user and only become the
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48 | <systemitem class='username'>root</systemitem> user when installing the
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49 | software. This philosophy is followed in all the packages in this book.
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50 | Unless otherwise specified, all instructions should be executed as an
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51 | unprivileged user. The book will advise you on instructions that need
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52 | <systemitem class='username'>root</systemitem> privileges.</para>
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53 |
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54 | </sect2>
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55 |
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56 | <sect2>
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57 | <title>Unpacking the Software</title>
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58 |
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59 | <para>If a file is in <filename class='extension'>.tar</filename> format
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60 | and compressed, it is unpacked by running one of the following
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61 | commands:</para>
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62 |
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63 | <screen><userinput>tar -xvf filename.tar.gz
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64 | tar -xvf filename.tgz
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65 | tar -xvf filename.tar.Z
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66 | tar -xvf filename.tar.bz2</userinput></screen>
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67 |
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68 | <note>
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69 | <para>You may omit using the <option>v</option> parameter in the commands
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70 | shown above and below if you wish to suppress the verbose listing of all
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71 | the files in the archive as they are extracted. This can help speed up the
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72 | extraction as well as make any errors produced during the extraction
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73 | more obvious to you.</para>
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74 | </note>
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75 |
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76 | <para>You can also use a slightly different method:</para>
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77 |
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78 | <screen><userinput>bzcat filename.tar.bz2 | tar -xv</userinput></screen>
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79 |
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80 | <para>Finally, you sometimes need to be able to unpack patches which are
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81 | generally not in <filename class='extension'>.tar</filename> format. The
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82 | best way to do this is to copy the patch file to the parent of the 'build'
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83 | directory and then run one of the following commands depending on whether
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84 | the file is a <filename class='extension'>.gz</filename> or <filename
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85 | class='extension'>.bz2</filename> file:</para>
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86 |
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87 | <screen><userinput>gunzip -v patchname.gz
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88 | bunzip2 -v patchname.bz2</userinput></screen>
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89 |
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90 | </sect2>
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91 |
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92 | <sect2>
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93 | <title>Verifying File Integrity</title>
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94 |
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95 | <para>Generally, to verify that the downloaded file is complete,
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96 | many package maintainers also distribute md5sums of the files. To verify the
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97 | md5sum of the downloaded files, download both the file and the
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98 | corresponding md5sum file to the same directory (preferably from different
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99 | on-line locations), and (assuming <filename>file.md5sum</filename> is the
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100 | md5sum file downloaded) run the following command:</para>
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101 |
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102 | <screen><userinput>md5sum -c file.md5sum</userinput></screen>
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103 |
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104 | <para>If there are any errors, they will be reported. Note that the BLFS
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105 | book includes md5sums for all the source files also. To use the BLFS
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106 | supplied md5sums, you can create a <filename>file.md5sum</filename> (place
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107 | the md5sum data and the exact name of the downloaded file on the same
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108 | line of a file, separated by white space) and run the command shown above.
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109 | Alternately, simply run the command shown below and compare the output
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110 | to the md5sum data shown in the BLFS book.</para>
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111 |
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112 | <screen><userinput>md5sum <replaceable><name_of_downloaded_file></replaceable></userinput></screen>
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113 |
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114 | <para>MD5 is not cryptographically secure, so the md5sums are only
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115 | provided for detecting unmalicious changes to the file content. For
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116 | example, an error or truncation introduced during network transfer, or
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117 | a <quote>stealth</quote> update to the package from the upstream
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118 | (updating the content of a released tarball instead of making a new
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119 | release properly).</para>
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120 |
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121 | <para>There is no <quote>100%</quote> secure way to make
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122 | sure the genuity of the source files. Assuming the upstream is managing
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123 | their website correctly (the private key is not leaked and the domain is
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124 | not hijacked), and the trust anchors have been set up correctly using
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125 | <xref linkend="make-ca"/> on the BLFS system, we can reasonably trust
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126 | download URLs to the upstream official website
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127 | <emphasis role="bold">with https protocol</emphasis>. Note that
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128 | BLFS book itself is published on a website with https, so you should
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129 | already have some confidence in https protocol or you wouldn't trust the
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130 | book content.</para>
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131 |
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132 | <para>If the package is downloaded from an unofficial location (for
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133 | example a local mirror), checksums generated by cryptographically secure
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134 | digest algorithms (for example SHA256) can be used to verify the
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135 | genuity of the package. Download the checksum file from the upstream
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136 | <emphasis role="bold">official</emphasis> website (or somewhere
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137 | <emphasis role="bold">you can trust</emphasis>) and compare the
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138 | checksum of the package from unofficial location with it. For example,
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139 | SHA256 checksum can be checked with the command:</para>
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140 |
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141 | <note>
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142 | <para>If the checksum and the package are downloaded from the same
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143 | untrusted location, you won't gain security enhancement by verifying
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144 | the package with the checksum. The attacker can fake the checksum as
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145 | well as compromising the package itself.</para>
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146 | </note>
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147 |
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148 | <screen><userinput>sha256sum -c <replaceable>file</replaceable>.sha256sum</userinput></screen>
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149 |
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150 | <para>If <xref linkend="gnupg2"/> is installed, you can also verify the
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151 | genuity of the package with a GPG signature. Import the upstream GPG
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152 | public key with:</para>
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153 |
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154 | <screen><userinput>gpg --recv-key <replaceable>keyID</replaceable></userinput></screen>
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155 |
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156 | <para><replaceable>keyID</replaceable> should be replaced with the key ID
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157 | from somewhere <emphasis role="bold">you can trust</emphasis> (for
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158 | example, copy it from the upstream official website using https). Now
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159 | you can verify the signature with:</para>
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160 |
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161 | <screen><userinput>gpg --recv-key <replaceable>file</replaceable>.sig <replaceable>file</replaceable></userinput></screen>
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162 |
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163 | <para>The advantage of <application>GnuPG</application> signature is,
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164 | once you imported a public key which can be trusted, you can download
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165 | both the package and its signature from the same unofficial location and
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166 | verify them with the public key. So you won't need to connect to the
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167 | official upstream website to retrieve a checksum for each new release.
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168 | You only need to update the public key if it's expired or revoked.
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169 | </para>
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170 |
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171 | </sect2>
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172 |
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173 | <sect2>
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174 | <title>Creating Log Files During Installation</title>
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175 |
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176 | <para>For larger packages, it is convenient to create log files instead of
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177 | staring at the screen hoping to catch a particular error or warning. Log
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178 | files are also useful for debugging and keeping records. The following
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179 | command allows you to create an installation log. Replace
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180 | <replaceable><command></replaceable> with the command you intend to execute.</para>
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181 |
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182 | <screen><userinput>( <replaceable><command></replaceable> 2>&1 | tee compile.log && exit $PIPESTATUS )</userinput></screen>
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183 |
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184 | <para><option>2>&1</option> redirects error messages to the same
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185 | location as standard output. The <command>tee</command> command allows
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186 | viewing of the output while logging the results to a file. The parentheses
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187 | around the command run the entire command in a subshell and finally the
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188 | <command>exit $PIPESTATUS</command> command ensures the result of the
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189 | <replaceable><command></replaceable> is returned as the result and not the
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190 | result of the <command>tee</command> command.</para>
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191 |
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192 | </sect2>
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193 |
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194 | <sect2 id="parallel-builds" xreflabel="Using Multiple Processors">
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195 | <title>Using Multiple Processors</title>
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196 |
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197 | <para>For many modern systems with multiple processors (or cores) the
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198 | compilation time for a package can be reduced by performing a "parallel
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199 | make" by either setting an environment variable or telling the make program
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200 | how many processors are available. For instance, a Core2Duo can support two
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201 | simultaneous processes with: </para>
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202 |
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203 | <screen><userinput>export MAKEFLAGS='-j2'</userinput></screen>
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204 |
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205 | <para>or just building with:</para>
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206 |
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207 | <screen><userinput>make -j2</userinput></screen>
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208 |
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209 | <para>
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210 | If you have applied the optional <command>sed</command> when building
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211 | <application>ninja</application> in LFS, you can use:
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212 | </para>
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213 |
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214 | <screen><userinput>export NINJAJOBS=2</userinput></screen>
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215 |
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216 | <para>
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217 | when a package uses <command>ninja</command>, or just:
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218 | </para>
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219 |
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220 | <screen><userinput>ninja -j2</userinput></screen>
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221 |
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222 | <para>
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223 | but for ninja, the default number of jobs is <N>+2, where <N>
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224 | is the number of processors available, so that using the above commands
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225 | is rather for limiting the number of jobs (see below for why this could
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226 | be necessary).
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227 | </para>
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228 |
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229 | <para>Generally the number of processes should not exceed the number of
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230 | cores supported by the CPU. To list the processors on your
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231 | system, issue: <userinput>grep processor /proc/cpuinfo</userinput>.
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232 | </para>
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233 |
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234 | <para>In some cases, using multiple processes may result in a 'race'
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235 | condition where the success of the build depends on the order of the
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236 | commands run by the <command>make</command> program. For instance, if an
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237 | executable needs File A and File B, attempting to link the program before
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238 | one of the dependent components is available will result in a failure.
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239 | This condition usually arises because the upstream developer has not
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240 | properly designated all the prerequisites needed to accomplish a step in the
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241 | Makefile.</para>
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242 |
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243 | <para>If this occurs, the best way to proceed is to drop back to a
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244 | single processor build. Adding '-j1' to a make command will override
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245 | the similar setting in the <envar>MAKEFLAGS</envar> environment
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246 | variable.</para>
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247 |
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248 | <note><para>When running the package tests or the install portion of the
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249 | package build process, we do not recommend using an option greater than
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250 | '-j1' unless specified otherwise. The installation procedures or checks
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251 | have not been validated using parallel procedures and may fail with issues
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252 | that are difficult to debug.</para></note>
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253 |
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254 | <important>
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255 | <para>
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256 | Another problem may occur with modern CPU's, which have a lot of cores.
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257 | Each job started consumes memory, and if the sum of the needed
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258 | memory for each job exceeds the available memory, you may encounter
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259 | either an OOM (Out of Memory) kernel interrupt or intense swapping
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260 | that will slow the build beyond reasonable limits.
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261 | </para>
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262 |
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263 | <para>
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264 | Some compilations with <command>g++</command> may consume up to 2.5 GB
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265 | of memory, so to be safe, you should restrict the number of jobs
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266 | to (Total Memory in GB)/2.5, at least for big packages such as LLVM,
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267 | WebKitGtk, QtWebEngine, or libreoffice.
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268 | </para>
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269 | </important>
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270 | </sect2>
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271 |
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272 | <sect2 id="automating-builds" xreflabel="Automated Building Procedures">
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273 | <title>Automated Building Procedures</title>
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274 |
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275 | <para>There are times when automating the building of a package can come in
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276 | handy. Everyone has their own reasons for wanting to automate building,
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277 | and everyone goes about it in their own way. Creating
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278 | <filename>Makefile</filename>s, <application>Bash</application> scripts,
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279 | <application>Perl</application> scripts or simply a list of commands used
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280 | to cut and paste are just some of the methods you can use to automate
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281 | building BLFS packages. Detailing how and providing examples of the many
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282 | ways you can automate the building of packages is beyond the scope of this
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283 | section. This section will expose you to using file redirection and the
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284 | <command>yes</command> command to help provide ideas on how to automate
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285 | your builds.</para>
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286 |
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287 | <bridgehead renderas="sect3">File Redirection to Automate Input</bridgehead>
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288 |
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289 | <para>You will find times throughout your BLFS journey when you will come
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290 | across a package that has a command prompting you for information. This
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291 | information might be configuration details, a directory path, or a response
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292 | to a license agreement. This can present a challenge to automate the
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293 | building of that package. Occasionally, you will be prompted for different
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294 | information in a series of questions. One method to automate this type of
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295 | scenario requires putting the desired responses in a file and using
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296 | redirection so that the program uses the data in the file as the answers to
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297 | the questions.</para>
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298 |
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299 | <para>Building the <application>CUPS</application> package is a good
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300 | example of how redirecting a file as input to prompts can help you automate
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301 | the build. If you run the test suite, you are asked to respond to a series
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302 | of questions regarding the type of test to run and if you have any
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303 | auxiliary programs the test can use. You can create a file with your
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304 | responses, one response per line, and use a command similar to the
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305 | one shown below to automate running the test suite:</para>
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306 |
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307 | <screen><userinput>make check < ../cups-1.1.23-testsuite_parms</userinput></screen>
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308 |
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309 | <para>This effectively makes the test suite use the responses in the file
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310 | as the input to the questions. Occasionally you may end up doing a bit of
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311 | trial and error determining the exact format of your input file for some
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312 | things, but once figured out and documented you can use this to automate
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313 | building the package.</para>
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314 |
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315 | <bridgehead renderas="sect3">Using <command>yes</command> to Automate
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316 | Input</bridgehead>
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317 |
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318 | <para>Sometimes you will only need to provide one response, or provide the
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319 | same response to many prompts. For these instances, the
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320 | <command>yes</command> command works really well. The
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321 | <command>yes</command> command can be used to provide a response (the same
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322 | one) to one or more instances of questions. It can be used to simulate
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323 | pressing just the <keycap>Enter</keycap> key, entering the
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324 | <keycap>Y</keycap> key or entering a string of text. Perhaps the easiest
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325 | way to show its use is in an example.</para>
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326 |
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327 | <para>First, create a short <application>Bash</application> script by
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328 | entering the following commands:</para>
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329 |
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330 | <screen><userinput>cat > blfs-yes-test1 << "EOF"
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331 | <literal>#!/bin/bash
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332 |
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333 | echo -n -e "\n\nPlease type something (or nothing) and press Enter ---> "
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334 |
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335 | read A_STRING
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336 |
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337 | if test "$A_STRING" = ""; then A_STRING="Just the Enter key was pressed"
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338 | else A_STRING="You entered '$A_STRING'"
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339 | fi
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340 |
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341 | echo -e "\n\n$A_STRING\n\n"</literal>
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342 | EOF
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343 | chmod 755 blfs-yes-test1</userinput></screen>
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344 |
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345 | <para>Now run the script by issuing <command>./blfs-yes-test1</command> from
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346 | the command line. It will wait for a response, which can be anything (or
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347 | nothing) followed by the <keycap>Enter</keycap> key. After entering
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348 | something, the result will be echoed to the screen. Now use the
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349 | <command>yes</command> command to automate the entering of a
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350 | response:</para>
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351 |
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352 | <screen><userinput>yes | ./blfs-yes-test1</userinput></screen>
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353 |
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354 | <para>Notice that piping <command>yes</command> by itself to the script
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355 | results in <keycap>y</keycap> being passed to the script. Now try it with a
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356 | string of text:</para>
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357 |
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358 | <screen><userinput>yes 'This is some text' | ./blfs-yes-test1</userinput></screen>
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359 |
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360 | <para>The exact string was used as the response to the script. Finally,
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361 | try it using an empty (null) string:</para>
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362 |
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363 | <screen><userinput>yes '' | ./blfs-yes-test1</userinput></screen>
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364 |
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365 | <para>Notice this results in passing just the press of the
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366 | <keycap>Enter</keycap> key to the script. This is useful for times when the
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367 | default answer to the prompt is sufficient. This syntax is used in the
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368 | <xref linkend="net-tools-automate-example"/> instructions to accept all the
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369 | defaults to the many prompts during the configuration step. You may now
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370 | remove the test script, if desired.</para>
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371 |
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372 | <bridgehead renderas="sect3">File Redirection to Automate Output</bridgehead>
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373 |
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374 | <para>In order to automate the building of some packages, especially those
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375 | that require you to read a license agreement one page at a time, requires
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376 | using a method that avoids having to press a key to display each page.
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377 | Redirecting the output to a file can be used in these instances to assist
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378 | with the automation. The previous section on this page touched on creating
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379 | log files of the build output. The redirection method shown there used the
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380 | <command>tee</command> command to redirect output to a file while also
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381 | displaying the output to the screen. Here, the output will only be sent to
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382 | a file.</para>
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383 |
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384 | <para>Again, the easiest way to demonstrate the technique is to show an
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385 | example. First, issue the command:</para>
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386 |
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387 | <screen><userinput>ls -l /usr/bin | more</userinput></screen>
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388 |
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389 | <para>Of course, you'll be required to view the output one page at a time
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390 | because the <command>more</command> filter was used. Now try the same
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391 | command, but this time redirect the output to a file. The special file
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392 | <filename>/dev/null</filename> can be used instead of the filename shown,
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393 | but you will have no log file to examine:</para>
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394 |
|
---|
395 | <screen><userinput>ls -l /usr/bin | more > redirect_test.log 2>&1</userinput></screen>
|
---|
396 |
|
---|
397 | <para>Notice that this time the command immediately returned to the shell
|
---|
398 | prompt without having to page through the output. You may now remove the
|
---|
399 | log file.</para>
|
---|
400 |
|
---|
401 | <para>The last example will use the <command>yes</command> command in
|
---|
402 | combination with output redirection to bypass having to page through the
|
---|
403 | output and then provide a <keycap>y</keycap> to a prompt. This technique
|
---|
404 | could be used in instances when otherwise you would have to page through
|
---|
405 | the output of a file (such as a license agreement) and then answer the
|
---|
406 | question of <quote>do you accept the above?</quote>. For this example,
|
---|
407 | another short <application>Bash</application> script is required:</para>
|
---|
408 |
|
---|
409 | <screen><userinput>cat > blfs-yes-test2 << "EOF"
|
---|
410 | <literal>#!/bin/bash
|
---|
411 |
|
---|
412 | ls -l /usr/bin | more
|
---|
413 |
|
---|
414 | echo -n -e "\n\nDid you enjoy reading this? (y,n) "
|
---|
415 |
|
---|
416 | read A_STRING
|
---|
417 |
|
---|
418 | if test "$A_STRING" = "y"; then A_STRING="You entered the 'y' key"
|
---|
419 | else A_STRING="You did NOT enter the 'y' key"
|
---|
420 | fi
|
---|
421 |
|
---|
422 | echo -e "\n\n$A_STRING\n\n"</literal>
|
---|
423 | EOF
|
---|
424 | chmod 755 blfs-yes-test2</userinput></screen>
|
---|
425 |
|
---|
426 | <para>This script can be used to simulate a program that requires you to
|
---|
427 | read a license agreement, then respond appropriately to accept the
|
---|
428 | agreement before the program will install anything. First, run the script
|
---|
429 | without any automation techniques by issuing
|
---|
430 | <command>./blfs-yes-test2</command>.</para>
|
---|
431 |
|
---|
432 | <para>Now issue the following command which uses two automation techniques,
|
---|
433 | making it suitable for use in an automated build script:</para>
|
---|
434 |
|
---|
435 | <screen><userinput>yes | ./blfs-yes-test2 > blfs-yes-test2.log 2>&1</userinput></screen>
|
---|
436 |
|
---|
437 | <para>If desired, issue <command>tail blfs-yes-test2.log</command> to see
|
---|
438 | the end of the paged output, and confirmation that <keycap>y</keycap> was
|
---|
439 | passed through to the script. Once satisfied that it works as it should,
|
---|
440 | you may remove the script and log file.</para>
|
---|
441 |
|
---|
442 | <para>Finally, keep in mind that there are many ways to automate and/or
|
---|
443 | script the build commands. There is not a single <quote>correct</quote> way
|
---|
444 | to do it. Your imagination is the only limit.</para>
|
---|
445 |
|
---|
446 | </sect2>
|
---|
447 |
|
---|
448 | <sect2>
|
---|
449 | <title>Dependencies</title>
|
---|
450 |
|
---|
451 | <para>For each package described, BLFS lists the known dependencies.
|
---|
452 | These are listed under several headings, whose meaning is as follows:</para>
|
---|
453 |
|
---|
454 | <itemizedlist>
|
---|
455 | <listitem>
|
---|
456 | <para><emphasis>Required</emphasis> means that the target package
|
---|
457 | cannot be correctly built without the dependency having first been
|
---|
458 | installed.</para>
|
---|
459 | </listitem>
|
---|
460 | <listitem>
|
---|
461 | <para><emphasis>Recommended</emphasis> means that BLFS strongly
|
---|
462 | suggests this package is installed first for a clean and trouble-free
|
---|
463 | build, that won't have issues either during the build process, or at
|
---|
464 | run-time. The instructions in the book assume these packages are
|
---|
465 | installed. Some changes or workarounds may be required if these
|
---|
466 | packages are not installed.</para>
|
---|
467 | </listitem>
|
---|
468 | <listitem>
|
---|
469 | <para><emphasis>Optional</emphasis> means that this package might be
|
---|
470 | installed for added functionality. Often BLFS will describe the
|
---|
471 | dependency to explain the added functionality that will result.</para>
|
---|
472 | </listitem>
|
---|
473 | </itemizedlist>
|
---|
474 |
|
---|
475 | </sect2>
|
---|
476 |
|
---|
477 | <sect2 id="package_updates">
|
---|
478 | <title>Using the Most Current Package Sources</title>
|
---|
479 |
|
---|
480 | <para>On occasion you may run into a situation in the book when a package
|
---|
481 | will not build or work properly. Though the Editors attempt to ensure
|
---|
482 | that every package in the book builds and works properly, sometimes a
|
---|
483 | package has been overlooked or was not tested with this particular version
|
---|
484 | of BLFS.</para>
|
---|
485 |
|
---|
486 | <para>If you discover that a package will not build or work properly, you
|
---|
487 | should see if there is a more current version of the package. Typically
|
---|
488 | this means you go to the maintainer's web site and download the most current
|
---|
489 | tarball and attempt to build the package. If you cannot determine the
|
---|
490 | maintainer's web site by looking at the download URLs, use Google and query
|
---|
491 | the package's name. For example, in the Google search bar type:
|
---|
492 | 'package_name download' (omit the quotes) or something similar. Sometimes
|
---|
493 | typing: 'package_name home page' will result in you finding the
|
---|
494 | maintainer's web site.</para>
|
---|
495 |
|
---|
496 | </sect2>
|
---|
497 |
|
---|
498 | <sect2 id="stripping">
|
---|
499 | <title>Stripping One More Time</title>
|
---|
500 |
|
---|
501 | <warning>
|
---|
502 | <para>If you did not strip programs and libraries in LFS,
|
---|
503 | the following will probably make your system unusable. To avoid that,
|
---|
504 | run the instructions at <ulink url="&lfs-root;/chapter08/strippingagain.html"/>
|
---|
505 | instead. After the critical files are stripped using those instructions,
|
---|
506 | the instructions below can be run any time new packages are installed.
|
---|
507 | </para>
|
---|
508 | </warning>
|
---|
509 |
|
---|
510 | <para>
|
---|
511 | In LFS, stripping of debugging symbols was discussed a couple of
|
---|
512 | times. When building BLFS packages, there are generally no special
|
---|
513 | instructions that discuss stripping again. It is probably not a good
|
---|
514 | idea to strip an executable or a library while it is in use, so exiting
|
---|
515 | any windowing environment is a good idea. Then you can do:
|
---|
516 | </para>
|
---|
517 |
|
---|
518 | <screen><userinput>find /usr/{bin,lib,sbin} \
|
---|
519 | -type f \( -name \*.so* -a ! -name \*dbg \) \
|
---|
520 | -exec strip --strip-unneeded {} \;</userinput></screen>
|
---|
521 |
|
---|
522 | <para>
|
---|
523 | If you install programs in other directories such as <filename
|
---|
524 | class="directory">/opt</filename> or <filename
|
---|
525 | class="directory">/usr/local</filename>, you may want to strip the files
|
---|
526 | there too.
|
---|
527 | </para>
|
---|
528 |
|
---|
529 | <para>
|
---|
530 | For more information on stripping, see <ulink
|
---|
531 | url="http://www.technovelty.org/linux/stripping-shared-libraries.html"/>.
|
---|
532 | </para>
|
---|
533 |
|
---|
534 | </sect2>
|
---|
535 | <!--
|
---|
536 | <sect2 id="libtool">
|
---|
537 | <title>Libtool files</title>
|
---|
538 |
|
---|
539 | <para>
|
---|
540 | One of the side effects of packages that use Autotools, including
|
---|
541 | libtool, is that they create many files with an .la extension. These
|
---|
542 | files are not needed in an LFS environment. If there are conflicts with
|
---|
543 | pkgconfig entries, they can actually prevent successful builds. You
|
---|
544 | may want to consider removing these files periodically:
|
---|
545 | </para>
|
---|
546 |
|
---|
547 | <screen><userinput>find /lib /usr/lib -not -path "*Image*" -a -name \*.la -delete</userinput></screen>
|
---|
548 |
|
---|
549 | <para>
|
---|
550 | The above command removes all .la files with the exception of those that
|
---|
551 | have <quote>Image</quote> or <quote>openldap</quote> as a part of the
|
---|
552 | path. These .la files are used by the ImageMagick and openldap programs,
|
---|
553 | respectively. There may be other exceptions by packages not in BLFS.
|
---|
554 | </para>
|
---|
555 |
|
---|
556 | </sect2>
|
---|
557 | -->
|
---|
558 | <sect2 id="buildsystems">
|
---|
559 | <title>Working with different build systems</title>
|
---|
560 |
|
---|
561 | <para>
|
---|
562 | There are now three different build systems in common use for
|
---|
563 | converting C or C++ source code into compiled programs or
|
---|
564 | libraries and their details (particularly, finding out about available
|
---|
565 | options and their default values) differ. It may be easiest to understand
|
---|
566 | the issues caused by some choices (typically slow execution or
|
---|
567 | unexpected use of, or omission of, optimizatons) by starting with
|
---|
568 | the CFLAGS and CXXFLAGS environment variables. There are also some
|
---|
569 | programs which use rust.
|
---|
570 | </para>
|
---|
571 |
|
---|
572 | <para>
|
---|
573 | Most LFS and BLFS builders are probably aware of the basics of CFLAGS
|
---|
574 | and CXXFLAGS for altering how a program is compiled. Typically, some
|
---|
575 | form of optimization is used by upstream developers (-O2 or -O3),
|
---|
576 | sometimes with the creation of debug symbols (-g), as defaults.
|
---|
577 | </para>
|
---|
578 |
|
---|
579 | <para>
|
---|
580 | If there are contradictory flags (e.g. multiple different -O values),
|
---|
581 | the <emphasis>last</emphasis> value will be used. Sometimes this means
|
---|
582 | that flags specified in environment variables will be picked up before
|
---|
583 | values hardcoded in the Makefile, and therefore ignored. For example,
|
---|
584 | where a user specifies '-O2' and that is followed by '-O3' the build will
|
---|
585 | use '-O3'.
|
---|
586 | </para>
|
---|
587 |
|
---|
588 | <para>
|
---|
589 | There are various other things which can be passed in CFLAGS or
|
---|
590 | CXXFLAGS, such as forcing compilation for a specific microarchitecture
|
---|
591 | (e.g. -march=amdfam10, -march=native) or specifying a specific standard
|
---|
592 | for C or C++ (-std=c++17 for example). But one thing which has now come
|
---|
593 | to light is that programmers might include debug assertions in their
|
---|
594 | code, expecting them to be disabled in releases by using -DNDEBUG.
|
---|
595 | Specifically, if <xref linkend="mesa"/> is built with these assertions
|
---|
596 | enabled, some activities such as loading levels of games can take
|
---|
597 | extremely long times, even on high-class video cards.
|
---|
598 | </para>
|
---|
599 |
|
---|
600 | <bridgehead renderas="sect3" id="autotools-info">Autotools with Make</bridgehead>
|
---|
601 |
|
---|
602 | <para>
|
---|
603 | This combination is often described as 'CMMI' (configure, make, make
|
---|
604 | install) and is used here to also cover the few packages which have a
|
---|
605 | configure script that is not generated by autotools.
|
---|
606 | </para>
|
---|
607 |
|
---|
608 | <para>
|
---|
609 | Sometimes running <command>./configure --help</command> will produce
|
---|
610 | useful options about switches which might be used. At other times,
|
---|
611 | after looking at the output from configure you may need to look
|
---|
612 | at the details of the script to find out what it was actually searching
|
---|
613 | for.
|
---|
614 | </para>
|
---|
615 |
|
---|
616 | <para>
|
---|
617 | Many configure scripts will pick up any CFLAGS or CXXFLAGS from the
|
---|
618 | environment, but CMMI packages vary about how these will be mixed with
|
---|
619 | any flags which would otherwise be used (<emphasis>variously</emphasis>:
|
---|
620 | ignored, used to replace the programmer's suggestion, used before the
|
---|
621 | programmer's suggestion, or used after the programmer's suggestion).
|
---|
622 | </para>
|
---|
623 |
|
---|
624 | <para>
|
---|
625 | In most CMMI packages, running 'make' will list each command and run
|
---|
626 | it, interspersed with any warnings. But some packages try to be 'silent'
|
---|
627 | and only show which file they are compiling or linking instead of showing
|
---|
628 | the command line. If you need to inspect the command, either because of
|
---|
629 | an error, or just to see what options and flags are being used, adding
|
---|
630 | 'V=1' to the make invocation may help.
|
---|
631 | </para>
|
---|
632 |
|
---|
633 | <bridgehead renderas="sect3" id="cmake-info">CMake</bridgehead>
|
---|
634 |
|
---|
635 | <para>
|
---|
636 | CMake works in a very different way, and it has two backends which can
|
---|
637 | be used on BLFS: 'make' and 'ninja'. The default backend is make, but
|
---|
638 | ninja can be faster on large packages with multiple processors. To
|
---|
639 | use ninja, specify '-G Ninja' in the cmake command. However, there are
|
---|
640 | some packages which create fatal errors in their ninja files but build
|
---|
641 | successfully using the default of Unix Makefiles.
|
---|
642 | </para>
|
---|
643 |
|
---|
644 | <para>
|
---|
645 | The hardest part of using CMake is knowing what options you might wish
|
---|
646 | to specify. The only way to get a list of what the package knows about
|
---|
647 | is to run <command>cmake -LAH</command> and look at the output for that
|
---|
648 | default configuration.
|
---|
649 | </para>
|
---|
650 |
|
---|
651 | <para>
|
---|
652 | Perhaps the most-important thing about CMake is that it has a variety
|
---|
653 | of CMAKE_BUILD_TYPE values, and these affect the flags. The default
|
---|
654 | is that this is not set and no flags are generated. Any CFLAGS or
|
---|
655 | CXXFLAGS in the environment will be used. If the programmer has coded
|
---|
656 | any debug assertions, those will be enabled unless -DNDEBUG is used.
|
---|
657 | The following CMAKE_BUILD_TYPE values will generate the flags shown,
|
---|
658 | and these will come <emphasis>after</emphasis> any flags in the
|
---|
659 | environment and therefore take precedence.
|
---|
660 | </para>
|
---|
661 |
|
---|
662 | <itemizedlist>
|
---|
663 | <listitem>
|
---|
664 | <para>Debug : '-g'</para>
|
---|
665 | </listitem>
|
---|
666 | <listitem>
|
---|
667 | <para>Release : '-O3 -DNDEBUG'</para>
|
---|
668 | </listitem>
|
---|
669 | <listitem>
|
---|
670 | <para>RelWithDebInfo : '-O2 -g -DNDEBUG'</para>
|
---|
671 | </listitem>
|
---|
672 | <listitem>
|
---|
673 | <para>MinSizeRel : '-Os -DNDEBUG'</para>
|
---|
674 | </listitem>
|
---|
675 | </itemizedlist>
|
---|
676 |
|
---|
677 | <para>
|
---|
678 | CMake tries to produce quiet builds. To see the details of the commands
|
---|
679 | which are being run, use 'make VERBOSE=1' or 'ninja -v'.
|
---|
680 | </para>
|
---|
681 |
|
---|
682 | <bridgehead renderas="sect3" id="meson-info">Meson</bridgehead>
|
---|
683 |
|
---|
684 | <para>
|
---|
685 | Meson has some similarities to CMake, but many differences. To get
|
---|
686 | details of the defines that you may wish to change you can look at
|
---|
687 | <filename>meson_options.txt</filename> which is usually in the
|
---|
688 | top-level directory.
|
---|
689 | </para>
|
---|
690 |
|
---|
691 | <para>
|
---|
692 | If you have already configured the package by running
|
---|
693 | <command>meson</command> and now wish to change one or more settings,
|
---|
694 | you can either remove the build directory, recreate it, and use the
|
---|
695 | altered options, or within the build directory run <command>meson
|
---|
696 | configure</command>, e.g. to set an option:
|
---|
697 | </para>
|
---|
698 |
|
---|
699 | <screen><userinput>meson configure -D<some_option>=true</userinput></screen>
|
---|
700 |
|
---|
701 | <para>
|
---|
702 | If you do that, the file <filename>meson-private/cmd_line.txt</filename>
|
---|
703 | will show the <emphasis>last</emphasis> commands which were used.
|
---|
704 | </para>
|
---|
705 |
|
---|
706 | <para>
|
---|
707 | Meson provides the following buildtype values, and the flags they enable
|
---|
708 | come <emphasis>after</emphasis> any flags supplied in the environment and
|
---|
709 | therefore take precedence.
|
---|
710 | </para>
|
---|
711 |
|
---|
712 | <itemizedlist>
|
---|
713 | <listitem>
|
---|
714 | <para>plain : no added flags. This is for distributors to supply their
|
---|
715 | own CLFAGS, CXXFLAGS and LDFLAGS. There is no obvious reason to use
|
---|
716 | this in BLFS.</para>
|
---|
717 | </listitem>
|
---|
718 | <listitem>
|
---|
719 | <para>debug : '-g' - this is the default if nothing is specified
|
---|
720 | in either <filename>meson.build</filename> or the command line.
|
---|
721 | However it results large and slow binaries, so we should override
|
---|
722 | it in BLFS.</para>
|
---|
723 | </listitem>
|
---|
724 | <listitem>
|
---|
725 | <para>debugoptimized : '-O2 -g' : this is the default specified in
|
---|
726 | <filename>meson.build</filename> of some packages.</para>
|
---|
727 | </listitem>
|
---|
728 | <listitem>
|
---|
729 | <para>release : '-O3 -DNDEBUG' (but occasionally a package will force
|
---|
730 | -O2 here)</para>
|
---|
731 | </listitem>
|
---|
732 | </itemizedlist>
|
---|
733 |
|
---|
734 | <para>
|
---|
735 | Although the 'release' buildtype is described as enabling -DNDEBUG, and all
|
---|
736 | CMake Release builds pass that, it has so far only been observed (in
|
---|
737 | verbose builds) for <xref linkend="mesa"/>. That suggests that it might
|
---|
738 | only be used when there are debug assertions present.
|
---|
739 | </para>
|
---|
740 |
|
---|
741 | <para>
|
---|
742 | The -DNDEBUG flag can also be provided by passing
|
---|
743 | <command>-Db_ndebug=true</command>.
|
---|
744 | </para>
|
---|
745 |
|
---|
746 | <para>
|
---|
747 | To see the details of the commands which are being run in a package using
|
---|
748 | meson, use 'ninja -v'.
|
---|
749 | </para>
|
---|
750 |
|
---|
751 | <bridgehead renderas="sect3" id="rust-info">Rustc and Cargo</bridgehead>
|
---|
752 |
|
---|
753 | <para>
|
---|
754 | Most released rustc programs are provided as crates (source tarballs)
|
---|
755 | which will query a server to check current versions of dependencies
|
---|
756 | and then download them as necessary. These packages are built using
|
---|
757 | <command>cargo --release</command>. In theory, you can manipulate the
|
---|
758 | RUSTFLAGS to change the optimize-level (default is 3, like -O3, e.g.
|
---|
759 | <literal>-Copt-level=3</literal>) or to force it to build for the
|
---|
760 | machine it is being compiled on, using
|
---|
761 | <literal>-Ctarget-cpu=native</literal> but in practice this seems to
|
---|
762 | make no significant difference.
|
---|
763 | </para>
|
---|
764 |
|
---|
765 | <para>
|
---|
766 | If you find an interesting rustc program which is only provided as
|
---|
767 | unpackaged source, you should at least specify
|
---|
768 | <literal>RUSTFLAGS=-Copt-level=2</literal> otherwise it will do an
|
---|
769 | unoptimized compile with debug info and run <emphasis>much</emphasis>
|
---|
770 | slower.
|
---|
771 | </para>
|
---|
772 |
|
---|
773 | <para>
|
---|
774 | The rust developers seem to assume that everyone will compile on a
|
---|
775 | machine dedicated to producing builds, so by default all CPUs are used.
|
---|
776 | This can often be worked around, either by exporting
|
---|
777 | CARGO_BUILD_JOBS=<N> or passing --jobs <N> to cargo. For
|
---|
778 | compiling rustc itself, specifying --jobs <N> on invocations of
|
---|
779 | x.py (together with the <envar>CARGO_BUILD_JOBS</envar> environment
|
---|
780 | variable, which looks like a "belt and braces" approach but seems to be
|
---|
781 | necessary) mostly works. The exception is running the tests when building
|
---|
782 | rustc, some of them will nevertheless use all online CPUs, at least as of
|
---|
783 | rustc-1.42.0.
|
---|
784 | </para>
|
---|
785 |
|
---|
786 | </sect2>
|
---|
787 |
|
---|
788 | <sect2 id="optimizations">
|
---|
789 | <title>Optimizing the build</title>
|
---|
790 |
|
---|
791 | <para>
|
---|
792 | Many people will prefer to optimize compiles as they see fit, by providing
|
---|
793 | CFLAGS or CXXFLAGS. For an introduction to the options available with gcc
|
---|
794 | and g++ see <ulink
|
---|
795 | url="https://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html"/> and <ulink
|
---|
796 | url="https://gcc.gnu.org/onlinedocs/gcc/Instrumentation-Options.html"/>
|
---|
797 | and <command>info gcc</command>.
|
---|
798 |
|
---|
799 | </para>
|
---|
800 |
|
---|
801 | <para>
|
---|
802 | Some packages default to '-O2 -g', others to '-O3 -g', and if CFLAGS or
|
---|
803 | CXXFLAGS are supplied they might be added to the package's defaults,
|
---|
804 | replace the package's defaults, or even be ignored. There are details
|
---|
805 | on some desktop packages which were mostly current in April 2019 at
|
---|
806 | <ulink url="https://www.linuxfromscratch.org/~ken/tuning/"/> - in
|
---|
807 | particular, README.txt, tuning-1-packages-and-notes.txt, and
|
---|
808 | tuning-notes-2B.txt. The particular thing to remember is that if you
|
---|
809 | want to try some of the more interesting flags you may need to force
|
---|
810 | verbose builds to confirm what is being used.
|
---|
811 | </para>
|
---|
812 |
|
---|
813 | <para>
|
---|
814 | Clearly, if you are optimizing your own program you can spend time to
|
---|
815 | profile it and perhaps recode some of it if it is too slow. But for
|
---|
816 | building a whole system that approach is impractical. In general,
|
---|
817 | -O3 usually produces faster programs than -O2. Specifying
|
---|
818 | -march=native is also beneficial, but means that you cannot move the
|
---|
819 | binaries to an incompatible machine - this can also apply to newer
|
---|
820 | machines, not just to older machines. For example programs compiled for
|
---|
821 | 'amdfam10' run on old Phenoms, Kaveris, and Ryzens : but programs
|
---|
822 | compiled for a Kaveri will not run on a Ryzen because certain op-codes
|
---|
823 | are not present. Similarly, if you build for a Haswell not everything
|
---|
824 | will run on a SandyBridge.
|
---|
825 | </para>
|
---|
826 |
|
---|
827 | <para>
|
---|
828 | There are also various other options which some people claim are
|
---|
829 | beneficial. At worst, you get to recompile and test, and then
|
---|
830 | discover that in your usage the options do not provide a benefit.
|
---|
831 | </para>
|
---|
832 |
|
---|
833 | <para>
|
---|
834 | If building Perl or Python modules, or Qt packages which use qmake,
|
---|
835 | in general the CFLAGS and CXXFLAGS used are those which were used by
|
---|
836 | those 'parent' packages.
|
---|
837 | </para>
|
---|
838 |
|
---|
839 | </sect2>
|
---|
840 |
|
---|
841 | <sect2 id="hardening">
|
---|
842 | <title>Options for hardening the build</title>
|
---|
843 |
|
---|
844 | <para>
|
---|
845 | Even on desktop systems, there are still a lot of exploitable
|
---|
846 | vulnerabilities. For many of these, the attack comes via javascript
|
---|
847 | in a browser. Often, a series of vulnerabilities are used to gain
|
---|
848 | access to data (or sometimes to pwn, i.e. own, the machine and
|
---|
849 | install rootkits). Most commercial distros will apply various
|
---|
850 | hardening measures.
|
---|
851 | </para>
|
---|
852 |
|
---|
853 | <para>
|
---|
854 | For hardening options which are reasonably cheap, there is some
|
---|
855 | discussion in the 'tuning' link above (occasionally, one or more
|
---|
856 | of these options might be inappropriate for a package). These
|
---|
857 | options are -D_FORTIFY_SOURCE=2, -fstack-protector=strong, and
|
---|
858 | (for C++) -D_GLIBCXX_ASSERTIONS. On modern machines these should
|
---|
859 | only have a little impact on how fast things run, and often they
|
---|
860 | will not be noticeable.
|
---|
861 | </para>
|
---|
862 |
|
---|
863 | <para>
|
---|
864 | In the past, there was Hardened LFS where gcc (a much older version)
|
---|
865 | was forced to use hardening (with options to turn some of it off on a
|
---|
866 | per-package basis. What is being covered here is different - first you
|
---|
867 | have to make sure that the package is indeed using your added flags and
|
---|
868 | not over-riding them.
|
---|
869 | </para>
|
---|
870 |
|
---|
871 | <para>
|
---|
872 | The main distros use much more, such as RELRO (Relocation Read Only)
|
---|
873 | and perhaps -fstack-clash-protection. You may also encounter the
|
---|
874 | so-called 'userspace retpoline' (-mindirect-branch=thunk etc.) which
|
---|
875 | is the equivalent of the spectre mitigations applied to the linux
|
---|
876 | kernel in late 2018). The kernel mitigations caused a lot of complaints
|
---|
877 | about lost performance, if you have a production server you might wish
|
---|
878 | to consider testing that, along with the other available options, to
|
---|
879 | see if performance is still sufficient.
|
---|
880 | </para>
|
---|
881 |
|
---|
882 | <para>
|
---|
883 | Whilst gcc has many hardening options, clang/LLVM's strengths lie
|
---|
884 | elsewhere. Some options which gcc provides are said to be less effective
|
---|
885 | in clang/LLVM.
|
---|
886 | </para>
|
---|
887 |
|
---|
888 | </sect2>
|
---|
889 |
|
---|
890 | </sect1>
|
---|