[1118b17] | 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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[35a5259] | 8 | <sect1 id="ch-scripts-systemd-custom" revision="systemd">
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[1118b17] | 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 <filename>systemd-system.conf(5)</filename> manual page for details on
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| 25 | 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 revied 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>This is not necessary if there is a separate partition for
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| 57 | <filename class="directory">/tmp</filename> specified in
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| 58 | <filename>/etc/fstab</filename>.</para>
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| 59 |
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| 60 | </sect2>
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| 61 |
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| 62 | <sect2>
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| 63 | <title>Configuring Automatic File Creation and Deletion</title>
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| 64 |
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| 65 | <para>There are several services that create or delete files or
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| 66 | directories:</para>
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| 67 |
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| 68 | <itemizedlist>
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| 69 | <listitem><para>systemd-tmpfiles-clean.service</para></listitem>
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| 70 | <listitem><para>systemd-tmpfiles-setup-dev.service</para></listitem>
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| 71 | <listitem><para>systemd-tmpfiles-setup.service</para></listitem>
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| 72 | </itemizedlist>
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| 73 |
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| 74 | <para>The system location for the configuration files is
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| 75 | <filename>/usr/lib/tmpfiles.d/*.conf</filename>. The local
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| 76 | configuration files are in
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| 77 | <filename class="directory">/etc/tmpfiles.d</filename>. Files in
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| 78 | <filename class="directory">/etc/tmpfiles.d</filename> override
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| 79 | files with the same name in
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| 80 | <filename class="directory">/usr/lib/tmpfiles.d</filename>. See
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| 81 | <filename>tmpfiles.d(5)</filename> manual page for file format
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| 82 | details.</para>
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| 83 |
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| 84 | </sect2>
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| 85 |
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| 86 | <sect2>
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| 87 | <title>Overriding Default Services Behavior</title>
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| 88 |
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[e787b1f] | 89 | <para>The parameter of a unit can be overriden by creating a directory
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[1118b17] | 90 | and a configuration file in <filename
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| 91 | class="directory">/etc/systemd/system</filename>. For example:</para>
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| 92 |
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| 93 | <screen role="nodump"><userinput>mkdir -pv /etc/systemd/system/foobar.service.d
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| 94 |
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| 95 | cat > /etc/systemd/system/foobar.service.d/foobar.conf << EOF
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| 96 | <literal>[Service]
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| 97 | Restart=always
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| 98 | RestartSec=30</literal>
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| 99 | EOF</userinput></screen>
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| 100 |
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| 101 | <para>See <filename>systemd.unit(5)</filename> manual page for more
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| 102 | information. After creating the configuration file, run
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| 103 | <userinput>systemctl daemon-reload</userinput> and <userinput>systemctl
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| 104 | restart foobar</userinput> to activate the changes to a service.</para>
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| 105 |
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| 106 | </sect2>
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| 107 |
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| 108 | <sect2>
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| 109 | <title>Debugging the Boot Sequence</title>
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| 110 |
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| 111 | <para>Rather than plain shell scripts used in SysVinit or BSD style init
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[e787b1f] | 112 | systems, systemd uses a unified format for different types of startup
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[1118b17] | 113 | files (or units). The command <command>systemctl</command> is used to
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| 114 | enable, disable, controll state, and obtain status of unit files. Here
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| 115 | are some examples of frequently used commands:</para>
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| 116 |
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| 117 | <itemizedlist>
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| 118 | <listitem>
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| 119 | <para><command>systemctl list-units -t <replaceable><service></replaceable> [--all]</command>:
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| 120 | lists loaded unit files of type service.</para>
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| 121 | </listitem>
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| 122 | <listitem>
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| 123 | <para><command>systemctl list-units -t <replaceable><target></replaceable> [--all]</command>:
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| 124 | lists loaded unit files of type target.</para>
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| 125 | </listitem>
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| 126 | <listitem>
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| 127 | <para><command>systemctl show -p Wants <replaceable><multi-user.target></replaceable></command>:
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| 128 | shows all units that depend on the multi-user target. Targets are
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| 129 | special unit files that are anogalous to runlevels under
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| 130 | SysVinit.</para>
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| 131 | </listitem>
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| 132 | <listitem>
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| 133 | <para><command>systemctl status <replaceable><servicename.service></replaceable></command>:
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| 134 | shows the status of the servicename service. The .service extension
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| 135 | can be omitted if there are no other unit files with the same name,
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| 136 | such as .socket files (which create a listening socket that provides
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| 137 | similar functionality to inetd/xinetd).</para>
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| 138 | </listitem>
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| 139 | </itemizedlist>
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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>Working with the Systemd Journal</title>
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| 145 |
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[e787b1f] | 146 | <para>Logging on a system booted with systemd is handled with
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| 147 | systemd-journald (by default), rather than a typical unix syslog daemon.
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| 148 | You can also add a normal syslog daemon and have both work side by
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| 149 | side if desired. The systemd-journald program stores journal entries in a
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| 150 | binary format rather than a plain text log file. To assist with
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| 151 | parsing the file, the command <command>journalctl</command> is provided.
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| 152 | Here are some examples of frequently used commands:</para>
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[1118b17] | 153 |
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| 154 | <itemizedlist>
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| 155 | <listitem>
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| 156 | <para><command>journalctl -r</command>: shows all contents of the
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| 157 | journal in reverse chronological order.</para>
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| 158 | </listitem>
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| 159 | <listitem>
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| 160 | <para><command>journalctl -u <replaceable>UNIT</replaceable></command>:
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| 161 | shows the journal entries associated with the specified UNIT
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| 162 | file.</para>
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| 163 | </listitem>
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| 164 | <listitem>
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| 165 | <para><command>journalctl -b[=ID] -r</command>: shows the journal
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| 166 | entries since last successfull boot (or for boot ID) in reverse
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| 167 | chronological order.</para>
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| 168 | </listitem>
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| 169 | <listitem>
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| 170 | <para><command>journalctl -f</command>: povides functionality similar
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| 171 | to tail -f (follow).</para>
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| 172 | </listitem>
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| 173 | </itemizedlist>
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| 174 |
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| 175 | </sect2>
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[ab9b18b] | 176 |
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| 177 | <sect2>
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| 178 | <title>Long Running Processes</title>
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| 179 |
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| 180 | <para>Beginning with systemd-230, all user processes are killed when a
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| 181 | user session is ended, even if nohup is used, or the process uses
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| 182 | <function>daemon()</function> or <function>setsid()</function>. This is a
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| 183 | deliberate change from a historically permissive environment to a more
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| 184 | restrictive one. The new behavior may cause issues if you depend on long
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| 185 | running programs (e.g., <command>screen</command> or
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| 186 | <command>tmux</command>) to remain active after ending your user
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| 187 | session. There are three ways to enable lingering processes to remain after
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| 188 | a user session is ended.</para>
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| 189 |
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| 190 | <itemizedlist>
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| 191 | <listitem>
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| 192 | <para>
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| 193 | <emphasis>Enable process lingering for only needed users</emphasis>:
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[ab44d4bc] | 194 | normal users have permission to enable process lingering
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[ab9b18b] | 195 | with the command <command>loginctl enable-linger</command> for their
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| 196 | own user. System administrators can use the same command with a
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| 197 | <parameter>user</parameter> argument to enable for a user. That user
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| 198 | can then use the <command>systemd-run</command> command to start
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| 199 | long running processes. For example: <command>systemd-run --scope
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| 200 | --user /usr/bin/screen</command>. If you enable lingering for your
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| 201 | user, the user@.service will remain even after all login sessions are
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| 202 | closed, and will automatically start at system boot. This has the
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| 203 | advantage of explicitly allowing and disallowing processes to run
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| 204 | after the user session has ended, but breaks backwards compatibility
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| 205 | with tools like <command>nohup</command> and utilities that use
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| 206 | <function>deamon()</function>.
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| 207 | </para>
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| 208 | </listitem>
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| 209 | <listitem>
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| 210 | <para>
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| 211 | <emphasis>Enable system-wide process lingering</emphasis>:
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| 212 | you can set <parameter>KillUserProcesses=no</parameter> in
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| 213 | <filename>/etc/logind.conf</filename> to enable process lingering
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| 214 | globally for all users. This has the benefit of leaving the old
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| 215 | method available to all users at the expense of explicit control.
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| 216 | </para>
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| 217 | </listitem>
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| 218 | <listitem>
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| 219 | <para>
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| 220 | <emphasis>Disable at build-time</emphasis>: You can enable
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| 221 | lingering by default while building systemd by adding the switch
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| 222 | <parameter>--without-kill-user-processes</parameter> to the
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| 223 | <command>configure</command> command for systemd. This completely
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| 224 | disables the ability of systemd to kill user processes at session
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| 225 | end.
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| 226 | </para>
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| 227 | </listitem>
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| 228 | </itemizedlist>
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| 229 |
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| 230 | </sect2>
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| 231 |
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[1118b17] | 232 | </sect1>
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