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="ch-scripts-systemd-custom" revision="systemd">
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9 | <?dbhtml filename="systemd-custom.html"?>
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10 |
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11 | <title>Systemd Usage and Configuration</title>
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12 |
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13 | <indexterm zone="ch-scripts-systemd-custom">
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14 | <primary sortas="e-Systemd">Systemd Customization</primary>
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15 | </indexterm>
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16 |
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17 | <sect2>
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18 | <title>Basic Configuration</title>
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19 |
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20 | <para>The <filename>/etc/systemd/system.conf</filename> file contains a set
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21 | of options to control basic systemd operations. The default file has all
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22 | entries commented out with the default settings indicated. This file is
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23 | where the log level may be changed as well as some basic logging settings.
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24 | See the <filename>systemd-system.conf(5)</filename> manual page for details
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25 | on each configuration option.</para>
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26 |
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27 | </sect2>
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28 |
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29 | <sect2>
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30 | <title>Disabling Screen Clearing at Boot Time</title>
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31 |
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32 | <para>The normal behavior for systemd is to clear the screen at
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33 | the end of the boot sequence. If desired, this behavior may be
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34 | changed by running the following command:</para>
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35 |
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36 | <screen role="nodump"><userinput>mkdir -pv /etc/systemd/system/getty@tty1.service.d
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37 |
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38 | cat > /etc/systemd/system/getty@tty1.service.d/noclear.conf << EOF
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39 | <literal>[Service]
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40 | TTYVTDisallocate=no</literal>
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41 | EOF</userinput></screen>
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42 |
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43 | <para>The boot messages can always be reviewed by using the
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44 | <userinput>journalctl -b</userinput> command as the root user.</para>
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45 |
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46 | </sect2>
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47 |
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48 | <sect2>
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49 | <title>Disabling tmpfs for /tmp</title>
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50 |
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51 | <para>By default, <filename class="directory">/tmp</filename> is created as
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52 | a tmpfs. If this is not desired, it can be overridden by the following:</para>
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53 |
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54 | <screen role="nodump"><userinput>ln -sfv /dev/null /etc/systemd/system/tmp.mount</userinput></screen>
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55 |
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56 | <para>Alternatively, if a a separate partition for
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57 | <filename class="directory">/tmp</filename> is desired, specify that
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58 | partition in an <filename>/etc/fstab</filename> entry.</para>
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59 |
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60 | <warning>
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61 | <para>
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62 | Do not create the symbolic link above if a separate partition is used
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63 | for <filename class="directory">/tmp</filename>. This will prvent the
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64 | root file system (/) from being remounted r/w and make the system
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65 | unusable when booted.
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66 | </para>
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67 | </warning>
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68 |
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69 | </sect2>
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70 |
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71 | <sect2>
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72 | <title>Configuring Automatic File Creation and Deletion</title>
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73 |
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74 | <para>There are several services that create or delete files or
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75 | directories:</para>
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76 |
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77 | <itemizedlist>
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78 | <listitem><para>systemd-tmpfiles-clean.service</para></listitem>
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79 | <listitem><para>systemd-tmpfiles-setup-dev.service</para></listitem>
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80 | <listitem><para>systemd-tmpfiles-setup.service</para></listitem>
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81 | </itemizedlist>
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82 |
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83 | <para>The system location for the configuration files is
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84 | <filename>/usr/lib/tmpfiles.d/*.conf</filename>. The local
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85 | configuration files are in
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86 | <filename class="directory">/etc/tmpfiles.d</filename>. Files in
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87 | <filename class="directory">/etc/tmpfiles.d</filename> override
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88 | files with the same name in
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89 | <filename class="directory">/usr/lib/tmpfiles.d</filename>. See
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90 | <filename>tmpfiles.d(5)</filename> manual page for file format
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91 | details.</para>
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92 |
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93 | <para>
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94 | Note that the syntax for the
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95 | <filename>/usr/lib/tmpfiles.d/*.conf</filename> files can be
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96 | confusing. For example, the default deletion of files in the /tmp directory
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97 | is located in <filename>/usr/lib/tmpfiles.d/tmp.conf</filename> with
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98 | the line:
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99 |
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100 | <screen role="nodump">q /tmp 1777 root root 10d</screen>
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101 |
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102 | The type field, q, discusses creating a subvolume with quotas which
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103 | is really only applicable to btrfs filesystems. It references type v
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104 | which in turn references type d (directory). This then creates the
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105 | specified directory if is is not present and adjusts the permissions
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106 | and ownership as specified. Contents of the directory will be
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107 | subject to time based cleanup if the age argument is specified.
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108 | </para>
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109 |
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110 | <para>
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111 | If the default parameters are not desired, then the file should
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112 | be copied to <filename class="directory">/etc/tmpfiles.d</filename>
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113 | and edited as desired. For example:
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114 |
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115 | <screen role="nodump"><userinput>mkdir -p /etc/tempfiles.d
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116 | cp /usr/lib/tmpfiles.d/tmp.conf /etc/tempfiles.d</userinput></screen>
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117 | </para>
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118 |
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119 | </sect2>
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120 |
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121 | <sect2>
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122 | <title>Overriding Default Services Behavior</title>
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123 |
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124 | <para>The parameter of a unit can be overriden by creating a directory
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125 | and a configuration file in <filename
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126 | class="directory">/etc/systemd/system</filename>. For example:</para>
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127 |
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128 | <screen role="nodump"><userinput>mkdir -pv /etc/systemd/system/foobar.service.d
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129 |
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130 | cat > /etc/systemd/system/foobar.service.d/foobar.conf << EOF
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131 | <literal>[Service]
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132 | Restart=always
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133 | RestartSec=30</literal>
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134 | EOF</userinput></screen>
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135 |
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136 | <para>See <filename>systemd.unit(5)</filename> manual page for more
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137 | information. After creating the configuration file, run
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138 | <userinput>systemctl daemon-reload</userinput> and <userinput>systemctl
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139 | restart foobar</userinput> to activate the changes to a service.</para>
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140 |
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141 | </sect2>
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142 |
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143 | <sect2>
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144 | <title>Debugging the Boot Sequence</title>
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145 |
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146 | <para>Rather than plain shell scripts used in SysVinit or BSD style init
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147 | systems, systemd uses a unified format for different types of startup
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148 | files (or units). The command <command>systemctl</command> is used to
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149 | enable, disable, control state, and obtain status of unit files. Here
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150 | are some examples of frequently used commands:</para>
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151 |
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152 | <itemizedlist>
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153 | <listitem>
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154 | <para><command>systemctl list-units -t <replaceable><service></replaceable> [--all]</command>:
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155 | lists loaded unit files of type service.</para>
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156 | </listitem>
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157 | <listitem>
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158 | <para><command>systemctl list-units -t <replaceable><target></replaceable> [--all]</command>:
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159 | lists loaded unit files of type target.</para>
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160 | </listitem>
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161 | <listitem>
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162 | <para><command>systemctl show -p Wants <replaceable><multi-user.target></replaceable></command>:
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163 | shows all units that depend on the multi-user target. Targets are
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164 | special unit files that are anogalous to runlevels under
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165 | SysVinit.</para>
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166 | </listitem>
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167 | <listitem>
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168 | <para><command>systemctl status <replaceable><servicename.service></replaceable></command>:
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169 | shows the status of the servicename service. The .service extension
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170 | can be omitted if there are no other unit files with the same name,
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171 | such as .socket files (which create a listening socket that provides
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172 | similar functionality to inetd/xinetd).</para>
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173 | </listitem>
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174 | </itemizedlist>
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175 |
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176 | </sect2>
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177 |
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178 | <sect2>
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179 | <title>Working with the Systemd Journal</title>
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180 |
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181 | <para>Logging on a system booted with systemd is handled with
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182 | systemd-journald (by default), rather than a typical unix syslog daemon.
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183 | You can also add a normal syslog daemon and have both work side by
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184 | side if desired. The systemd-journald program stores journal entries in a
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185 | binary format rather than a plain text log file. To assist with
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186 | parsing the file, the command <command>journalctl</command> is provided.
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187 | Here are some examples of frequently used commands:</para>
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188 |
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189 | <itemizedlist>
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190 | <listitem>
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191 | <para><command>journalctl -r</command>: shows all contents of the
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192 | journal in reverse chronological order.</para>
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193 | </listitem>
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194 | <listitem>
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195 | <para><command>journalctl -u <replaceable>UNIT</replaceable></command>:
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196 | shows the journal entries associated with the specified UNIT
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197 | file.</para>
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198 | </listitem>
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199 | <listitem>
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200 | <para><command>journalctl -b[=ID] -r</command>: shows the journal
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201 | entries since last successful boot (or for boot ID) in reverse
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202 | chronological order.</para>
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203 | </listitem>
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204 | <listitem>
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205 | <para><command>journalctl -f</command>: povides functionality similar
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206 | to tail -f (follow).</para>
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207 | </listitem>
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208 | </itemizedlist>
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209 |
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210 | </sect2>
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211 |
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212 | <sect2>
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213 | <title>Long Running Processes</title>
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214 |
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215 | <para>Beginning with systemd-230, all user processes are killed when a user
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216 | session is ended, even if nohup is used, or the process uses the
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217 | <function>daemon()</function> or <function>setsid()</function> functions.
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218 | This is a deliberate change from a historically permissive environment to a
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219 | more restrictive one. The new behavior may cause issues if you depend on
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220 | long running programs (e.g., <command>screen</command> or
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221 | <command>tmux</command>) to remain active after ending your user session.
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222 | There are three ways to enable lingering processes to remain after a user
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223 | session is ended.</para>
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224 |
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225 | <itemizedlist>
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226 | <listitem>
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227 | <para>
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228 | <emphasis>Enable process lingering for only selected users</emphasis>:
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229 | Normal users have permission to enable process lingering
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230 | with the command <command>loginctl enable-linger</command> for their
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231 | own user. System administrators can use the same command with a
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232 | <parameter>user</parameter> argument to enable for a user. That user
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233 | can then use the <command>systemd-run</command> command to start
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234 | long running processes. For example: <command>systemd-run --scope
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235 | --user /usr/bin/screen</command>. If you enable lingering for your
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236 | user, the user@.service will remain even after all login sessions are
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237 | closed, and will automatically start at system boot. This has the
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238 | advantage of explicitly allowing and disallowing processes to run
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239 | after the user session has ended, but breaks backwards compatibility
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240 | with tools like <command>nohup</command> and utilities that use
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241 | <function>deamon()</function>.
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242 | </para>
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243 | </listitem>
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244 | <listitem>
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245 | <para>
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246 | <emphasis>Enable system-wide process lingering</emphasis>:
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247 | You can set <parameter>KillUserProcesses=no</parameter> in
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248 | <filename>/etc/logind.conf</filename> to enable process lingering
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249 | globally for all users. This has the benefit of leaving the old
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250 | method available to all users at the expense of explicit control.
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251 | </para>
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252 | </listitem>
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253 | <listitem>
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254 | <para>
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255 | <emphasis>Disable at build-time</emphasis>: You can enable
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256 | lingering by default while building systemd by adding the switch
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257 | <parameter>--without-kill-user-processes</parameter> to the
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258 | <command>configure</command> command for systemd. This completely
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259 | disables the ability of systemd to kill user processes at session
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260 | end.
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261 | </para>
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262 | </listitem>
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263 | </itemizedlist>
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264 |
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265 | </sect2>
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266 |
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267 | </sect1>
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