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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-config-usage"> |
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9 | <?dbhtml filename="usage.html"?> |
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10 | |
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11 | <title>How does Systemd work?</title> |
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12 | |
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13 | <indexterm zone="ch-config-usage"> |
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14 | <primary sortas="a-systemd">Systemd</primary> |
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15 | <secondary>usage</secondary></indexterm> |
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16 | |
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17 | <warning> |
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18 | <para>Please disregard this page until it is complete and verified.</para> |
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19 | </warning> |
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20 | |
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21 | <sect2> |
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22 | <title>Introduction to Systemd</title> |
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23 | |
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24 | |
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25 | <para>Systemd is a system management daemon designed exclusively for the |
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26 | Linux kernel API. In the Linux startup process, it is the first process to |
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27 | execute in user land; therefore, it is also the parent process of all child |
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28 | processes in user land.</para> |
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29 | |
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30 | <para>Systemd's initialization instructions for each daemon are recorded in |
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31 | a declarative configuration file rather than a shell script. For |
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32 | inter-process communication, systemd makes Unix domain sockets and D-Bus |
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33 | available to the running daemons. Because systemd tracks processes using |
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34 | Linux cgroups instead of process identifiers (PIDs), daemons cannot "escape" |
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35 | systemd; not even by double-forking. Systemd is also capable of aggressive |
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36 | parallelization.</para> |
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37 | |
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38 | <para>Among systemd's auxiliary features are a cron-like job scheduler |
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39 | called systemd Calendar Timers, and an event logging subsystem called |
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40 | journal. The system administrator may choose whether to log system events |
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41 | with systemd or syslog. Systemd's logfile is a binary file. The state of |
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42 | systemd itself can be preserved in a snapshot for future recall.</para> |
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43 | |
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44 | <para>Systemd provides a replacement for sysvinit, pm-utils, inetd, acpid, |
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45 | syslog, watchdog, cron and atd, and obsoletes ConsoleKit.</para> |
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46 | |
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47 | </sect2> |
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48 | |
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49 | <sect2> |
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50 | <title>Systemctl</title> |
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51 | |
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52 | <para><command>systemctl</command> is the main command used to introspect |
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53 | and control systemd.</para> |
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54 | |
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55 | <variablelist> |
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56 | |
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57 | <varlistentry> |
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58 | <term>List running units:</term> |
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59 | <listitem> |
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60 | <para><command>systemctl</command> or <command>systemctl list-units</command></para> |
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61 | </listitem> |
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62 | </varlistentry> |
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63 | |
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64 | <varlistentry> |
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65 | <term>List failed units:</term> |
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66 | <listitem> |
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67 | <para><command>systemctl --failed</command></para> |
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68 | </listitem> |
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69 | </varlistentry> |
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70 | |
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71 | <varlistentry> |
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72 | <term>List available unit files:</term> |
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73 | <listitem> |
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74 | <para><command>systemctl list-unit-files</command></para> |
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75 | </listitem> |
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76 | </varlistentry> |
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77 | |
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78 | <varlistentry> |
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79 | <term>Activate a unit immediately:</term> |
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80 | <listitem> |
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81 | <para><command>systemctl start</command> <replaceable>unit</replaceable></para> |
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82 | </listitem> |
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83 | </varlistentry> |
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84 | |
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85 | <varlistentry> |
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86 | <term>Stop a unit immediately:</term> |
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87 | <listitem> |
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88 | <para><command>systemctl stop </command><replaceable>unit</replaceable></para> |
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89 | </listitem> |
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90 | </varlistentry> |
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91 | |
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92 | <varlistentry> |
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93 | <term>Restart a unit:</term> |
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94 | <listitem> |
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95 | <para><command>systemctl restart </command><replaceable>unit</replaceable></para> |
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96 | </listitem> |
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97 | </varlistentry> |
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98 | |
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99 | <varlistentry> |
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100 | <term>Reload unit configuration:</term> |
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101 | <listitem> |
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102 | <para><command>systemctl reload </command><replaceable>unit</replaceable></para> |
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103 | </listitem> |
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104 | </varlistentry> |
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105 | |
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106 | <varlistentry> |
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107 | <term>Show status of a unit:</term> |
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108 | <listitem> |
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109 | <para><command>systemctl status </command><replaceable>unit</replaceable></para> |
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110 | </listitem> |
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111 | </varlistentry> |
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112 | |
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113 | <varlistentry> |
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114 | <term>Check if a unit is enabled or disabled:</term> |
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115 | <listitem> |
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116 | <para><command>systemctl is-enabled </command><replaceable>unit</replaceable></para> |
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117 | </listitem> |
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118 | </varlistentry> |
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119 | |
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120 | <varlistentry> |
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121 | <term>Enable a unit to start during boot:</term> |
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122 | <listitem> |
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123 | <para><command>systemctl enable </command><replaceable>unit</replaceable></para> |
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124 | </listitem> |
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125 | </varlistentry> |
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126 | |
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127 | <varlistentry> |
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128 | <term>Disable a unit to not start during boot:</term> |
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129 | <listitem> |
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130 | <para><command>systemctl disable </command><replaceable>unit</replaceable></para> |
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131 | </listitem> |
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132 | </varlistentry> |
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133 | |
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134 | <varlistentry> |
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135 | <term>Reload systemd and scan for new or changed units:</term> |
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136 | <listitem> |
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137 | <para><command>systemctl daemon-reload</command></para> |
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138 | </listitem> |
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139 | </varlistentry> |
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140 | |
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141 | </variablelist> |
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142 | |
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143 | <para>For more information regarding systemd, please refer to the systemd |
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144 | and related man-pages and |
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145 | <ulink url="https://fedoraproject.org/wiki/Systemd">Systemd at |
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146 | FedoraProject</ulink> for documentation, examples, features, and other |
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147 | information.</para> |
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148 | |
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149 | </sect2> |
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150 | |
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151 | </sect1> |
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