1 | <?xml version="1.0" encoding="UTF-8"?>
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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="ch-tools-createfiles">
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9 | <?dbhtml filename="createfiles.html"?>
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10 |
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11 | <title>Creating Essential Files and Symlinks</title>
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12 |
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13 | <indexterm zone="ch-tools-createfiles">
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14 | <primary sortas="e-/etc/passwd">/etc/passwd</primary>
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15 | </indexterm>
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16 |
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17 | <indexterm zone="ch-tools-createfiles">
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18 | <primary sortas="e-/etc/group">/etc/group</primary>
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19 | </indexterm>
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20 |
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21 | <indexterm zone="ch-tools-createfiles">
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22 | <primary sortas="e-/run/utmp">/run/utmp</primary>
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23 | </indexterm>
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24 |
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25 | <indexterm zone="ch-tools-createfiles">
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26 | <primary sortas="e-/var/log/btmp">/var/log/btmp</primary>
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27 | </indexterm>
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28 |
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29 | <indexterm zone="ch-tools-createfiles">
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30 | <primary sortas="e-/var/log/lastlog">/var/log/lastlog</primary>
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31 | </indexterm>
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32 |
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33 | <indexterm zone="ch-tools-createfiles">
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34 | <primary sortas="e-/var/log/wtmp">/var/log/wtmp</primary>
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35 | </indexterm>
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36 |
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37 | <para>Historically, Linux maintained a list of the mounted file systems in the
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38 | file <filename>/etc/mtab</filename>. Modern kernels maintain this list
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39 | internally and expose it to the user via the <filename
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40 | class="directory">/proc</filename> filesystem. To satisfy utilities that
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41 | expect to find <filename>/etc/mtab</filename>, create the following
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42 | symbolic link:</para>
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43 |
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44 | <screen><userinput>ln -sv /proc/self/mounts /etc/mtab</userinput></screen>
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45 |
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46 | <para>Create a basic <filename>/etc/hosts</filename> file to be
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47 | referenced in some test suites, and in one of Perl's configuration files
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48 | as well:</para>
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49 |
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50 | <screen><userinput>cat > /etc/hosts << EOF
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51 | <literal>127.0.0.1 localhost $(hostname)
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52 | ::1 localhost</literal>
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53 | EOF</userinput></screen>
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54 |
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55 | <para>In order for user <systemitem class="username">root</systemitem> to be
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56 | able to login and for the name <quote>root</quote> to be recognized, there
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57 | must be relevant entries in the <filename>/etc/passwd</filename> and
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58 | <filename>/etc/group</filename> files.</para>
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59 |
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60 | <para>Create the <filename>/etc/passwd</filename> file by running the following
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61 | command:</para>
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62 |
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63 | <screen revision="sysv"><userinput>cat > /etc/passwd << "EOF"
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64 | <literal>root:x:0:0:root:/root:/bin/bash
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65 | bin:x:1:1:bin:/dev/null:/usr/bin/false
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66 | daemon:x:6:6:Daemon User:/dev/null:/usr/bin/false
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67 | messagebus:x:18:18:D-Bus Message Daemon User:/run/dbus:/usr/bin/false
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68 | uuidd:x:80:80:UUID Generation Daemon User:/dev/null:/usr/bin/false
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69 | nobody:x:65534:65534:Unprivileged User:/dev/null:/usr/bin/false</literal>
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70 | EOF</userinput></screen>
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71 |
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72 | <screen revision="systemd"><userinput>cat > /etc/passwd << "EOF"
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73 | <literal>root:x:0:0:root:/root:/bin/bash
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74 | bin:x:1:1:bin:/dev/null:/usr/bin/false
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75 | daemon:x:6:6:Daemon User:/dev/null:/usr/bin/false
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76 | messagebus:x:18:18:D-Bus Message Daemon User:/run/dbus:/usr/bin/false
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77 | systemd-journal-gateway:x:73:73:systemd Journal Gateway:/:/usr/bin/false
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78 | systemd-journal-remote:x:74:74:systemd Journal Remote:/:/usr/bin/false
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79 | systemd-journal-upload:x:75:75:systemd Journal Upload:/:/usr/bin/false
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80 | systemd-network:x:76:76:systemd Network Management:/:/usr/bin/false
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81 | systemd-resolve:x:77:77:systemd Resolver:/:/usr/bin/false
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82 | systemd-timesync:x:78:78:systemd Time Synchronization:/:/usr/bin/false
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83 | systemd-coredump:x:79:79:systemd Core Dumper:/:/usr/bin/false
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84 | uuidd:x:80:80:UUID Generation Daemon User:/dev/null:/usr/bin/false
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85 | systemd-oom:x:81:81:systemd Out Of Memory Daemon:/:/usr/bin/false
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86 | nobody:x:65534:65534:Unprivileged User:/dev/null:/usr/bin/false</literal>
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87 | EOF</userinput></screen>
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88 |
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89 | <para>The actual password for <systemitem class="username">root</systemitem>
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90 | will be set later.</para>
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91 |
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92 | <para>Create the <filename>/etc/group</filename> file by running the following
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93 | command:</para>
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94 |
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95 | <screen revision="sysv"><userinput>cat > /etc/group << "EOF"
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96 | <literal>root:x:0:
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97 | bin:x:1:daemon
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98 | sys:x:2:
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99 | kmem:x:3:
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100 | tape:x:4:
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101 | tty:x:5:
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102 | daemon:x:6:
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103 | floppy:x:7:
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104 | disk:x:8:
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105 | lp:x:9:
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106 | dialout:x:10:
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107 | audio:x:11:
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108 | video:x:12:
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109 | utmp:x:13:
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110 | cdrom:x:15:
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111 | adm:x:16:
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112 | messagebus:x:18:
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113 | input:x:24:
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114 | mail:x:34:
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115 | kvm:x:61:
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116 | uuidd:x:80:
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117 | wheel:x:97:
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118 | users:x:999:
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119 | nogroup:x:65534:</literal>
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120 | EOF</userinput></screen>
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121 |
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122 | <screen revision="systemd"><userinput>cat > /etc/group << "EOF"
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123 | <literal>root:x:0:
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124 | bin:x:1:daemon
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125 | sys:x:2:
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126 | kmem:x:3:
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127 | tape:x:4:
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128 | tty:x:5:
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129 | daemon:x:6:
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130 | floppy:x:7:
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131 | disk:x:8:
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132 | lp:x:9:
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133 | dialout:x:10:
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134 | audio:x:11:
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135 | video:x:12:
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136 | utmp:x:13:
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137 | cdrom:x:15:
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138 | adm:x:16:
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139 | messagebus:x:18:
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140 | systemd-journal:x:23:
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141 | input:x:24:
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142 | mail:x:34:
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143 | kvm:x:61:
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144 | systemd-journal-gateway:x:73:
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145 | systemd-journal-remote:x:74:
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146 | systemd-journal-upload:x:75:
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147 | systemd-network:x:76:
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148 | systemd-resolve:x:77:
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149 | systemd-timesync:x:78:
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150 | systemd-coredump:x:79:
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151 | uuidd:x:80:
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152 | systemd-oom:x:81:
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153 | wheel:x:97:
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154 | users:x:999:
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155 | nogroup:x:65534:</literal>
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156 | EOF</userinput></screen>
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157 |
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158 | <para>The created groups are not part of any standard—they are groups
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159 | decided on in part by the requirements of the Udev configuration in Chapter
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160 | 9, and in part by common conventions employed by a number of existing Linux
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161 | distributions. In addition, some test suites rely on specific users or
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162 | groups. The Linux Standard Base (LSB, available at <ulink
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163 | url="https://refspecs.linuxfoundation.org/lsb.shtml"/>) only recommends that,
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164 | besides the group <systemitem class="groupname">root</systemitem> with a
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165 | Group ID (GID) of 0, a group <systemitem class="groupname">bin</systemitem>
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166 | with a GID of 1 be present. The GID of 5 is widely used for the
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167 | <systemitem class="groupname">tty</systemitem> group, and the number 5 is
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168 | also used in <phrase revision="systemd">systemd</phrase>
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169 | <phrase revision="sysv"><filename>/etc/fstab</filename></phrase> for the
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170 | <systemitem class="filesystem">devpts</systemitem> filesystem.
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171 | All other group names and GIDs can be chosen freely by the system
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172 | administrator since well-written programs do not depend on GID numbers,
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173 | but rather use the group's name.</para>
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174 |
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175 | <para>The ID 65534 is used by the kernel for NFS and separate user
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176 | namespaces for unmapped users and groups (those exist on the NFS server
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177 | or the parent user namespace, but <quote>do not exist</quote> on the local
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178 | machine or in the separate namespace). We assign
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179 | <systemitem class="username">nobody</systemitem> and
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180 | <systemitem class="groupname">nogroup</systemitem> to avoid an
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181 | unnamed ID. But other distros may treat this ID differently, so any
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182 | portable program should not depend on this assignment.</para>
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183 |
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184 | <para>Some tests in <xref linkend="chapter-building-system"/> need a regular
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185 | user. We add this user here and delete this account at the end of that
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186 | chapter.</para>
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187 |
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188 | <screen><userinput>echo "tester:x:101:101::/home/tester:/bin/bash" >> /etc/passwd
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189 | echo "tester:x:101:" >> /etc/group
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190 | install -o tester -d /home/tester</userinput></screen>
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191 |
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192 | <para>To remove the <quote>I have no name!</quote> prompt, start a new
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193 | shell. Since the
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194 | <filename>/etc/passwd</filename> and <filename>/etc/group</filename>
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195 | files have been created, user name and group name resolution will now
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196 | work:</para>
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197 |
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198 | <screen role="nodump"><userinput>exec /usr/bin/bash --login</userinput></screen>
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199 |
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200 | <para>The <command>login</command>, <command>agetty</command>, and
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201 | <command>init</command> programs (and others) use a number of log
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202 | files to record information such as who was logged into the system and
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203 | when. However, these programs will not write to the log files if they
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204 | do not already exist. Initialize the log files and give them
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205 | proper permissions:</para>
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206 |
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207 | <screen><userinput>touch /var/log/{btmp,lastlog,faillog,wtmp}
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208 | chgrp -v utmp /var/log/lastlog
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209 | chmod -v 664 /var/log/lastlog
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210 | chmod -v 600 /var/log/btmp</userinput></screen>
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211 |
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212 | <para>The <filename>/var/log/wtmp</filename> file records all logins and
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213 | logouts. The <filename>/var/log/lastlog</filename> file records when each
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214 | user last logged in. The <filename>/var/log/faillog</filename> file records
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215 | failed login attempts. The <filename>/var/log/btmp</filename> file records
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216 | the bad login attempts.</para>
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217 |
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218 | <!-- systemd no longer creates this -->
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219 | <note revision='sysv'><para>The <filename>/run/utmp</filename> file
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220 | records the users that are currently logged in. This file is created
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221 | dynamically in the boot scripts.</para></note>
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222 |
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223 | <!-- AFAIK they are not vital for system function, users requiring such
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224 | info should rely on systemd-logind or elogind or some custom PAM
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225 | module. Maybe we can stop to create them at all. -->
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226 | <note>
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227 | <para>
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228 | The <phrase revision='sysv'><filename>utmp</filename>,
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229 | </phrase><filename>wtmp</filename>, <filename>btmp</filename>, and
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230 | <filename>lastlog</filename> files use 32-bit integers for timestamps
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231 | and they'll be fundamentally broken after year 2038. Many packages
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232 | have stopped using them and other packages are going to stop using
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233 | them. It is probably best to consider them deprecated.
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234 | </para>
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235 | </note>
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236 |
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237 | </sect1>
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