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e8815abff6
For CI in mkosi, I want to configure systemd to log at debug level to the journal, but not to the console. While we already have max level settings for journald's forwarding settings, not every log line goes to the journal, specifically during early boot and when units are connected directly to the console (think systemd-firstboot), so let's extend the log level options we already have to allow specifying a comma separated list of values and lets allow prefixing values with the log target they apply to to make this possible.
220 lines
12 KiB
XML
220 lines
12 KiB
XML
<?xml version="1.0"?>
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<!DOCTYPE refsect1 PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd">
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<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
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<refsect1>
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<title>Environment</title>
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<variablelist class='environment-variables'>
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<varlistentry id='log-level'>
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<term><varname>$SYSTEMD_LOG_LEVEL</varname></term>
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<listitem><para id='log-level-body'>The maximum log level of emitted messages (messages with a higher
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log level, i.e. less important ones, will be suppressed). Takes a comma-separated list of values. A
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value may be either one of (in order of decreasing importance) <constant>emerg</constant>,
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<constant>alert</constant>, <constant>crit</constant>, <constant>err</constant>,
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<constant>warning</constant>, <constant>notice</constant>, <constant>info</constant>,
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<constant>debug</constant>, or an integer in the range 0…7. See
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<citerefentry project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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for more information. Each value may optionally be prefixed with one of <constant>console</constant>,
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<constant>syslog</constant>, <constant>kmsg</constant> or <constant>journal</constant> followed by a
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colon to set the maximum log level for that specific log target (e.g.
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<constant>SYSTEMD_LOG_LEVEL=debug,console:info</constant> specifies to log at debug level except when
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logging to the console which should be at info level). Note that the global maximum log level takes
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priority over any per target maximum log levels.</para></listitem>
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</varlistentry>
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<varlistentry id='log-color'>
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<term><varname>$SYSTEMD_LOG_COLOR</varname></term>
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<listitem><para id='log-color-body'>A boolean. If true, messages written to the tty will be colored
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according to priority.</para>
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<para>This setting is only useful when messages are written directly to the terminal, because
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<citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry> and
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other tools that display logs will color messages based on the log level on their own.</para>
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</listitem>
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</varlistentry>
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<varlistentry id='log-time'>
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<term><varname>$SYSTEMD_LOG_TIME</varname></term>
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<listitem><para id='log-time-body'>A boolean. If true, console log messages will be prefixed with a
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timestamp.</para>
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<para>This setting is only useful when messages are written directly to the terminal or a file, because
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<citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry> and
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other tools that display logs will attach timestamps based on the entry metadata on their own.</para>
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</listitem>
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</varlistentry>
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<varlistentry id='log-location'>
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<term><varname>$SYSTEMD_LOG_LOCATION</varname></term>
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<listitem><para id='log-location-body'>A boolean. If true, messages will be prefixed with a filename
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and line number in the source code where the message originates.</para>
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<para>Note that the log location is often attached as metadata to journal entries anyway. Including it
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directly in the message text can nevertheless be convenient when debugging programs.</para>
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</listitem>
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</varlistentry>
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<varlistentry id='log-tid'>
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<term><varname>$SYSTEMD_LOG_TID</varname></term>
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<listitem><para id='log-tid-body'>A boolean. If true, messages will be prefixed with the current
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numerical thread ID (TID).</para>
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<para>Note that the this information is attached as metadata to journal entries anyway. Including it
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directly in the message text can nevertheless be convenient when debugging programs.</para>
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</listitem>
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</varlistentry>
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<varlistentry id='log-target'>
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<term><varname>$SYSTEMD_LOG_TARGET</varname></term>
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<listitem><para id='log-target-body'>The destination for log messages. One of
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<constant>console</constant> (log to the attached tty), <constant>console-prefixed</constant> (log to
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the attached tty but with prefixes encoding the log level and "facility", see <citerefentry
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project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<constant>kmsg</constant> (log to the kernel circular log buffer), <constant>journal</constant> (log to
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the journal), <constant>journal-or-kmsg</constant> (log to the journal if available, and to kmsg
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otherwise), <constant>auto</constant> (determine the appropriate log target automatically, the default),
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<constant>null</constant> (disable log output).</para>
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<!-- <constant>syslog</constant>, <constant>syslog-or-kmsg</constant> are deprecated -->
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</listitem>
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</varlistentry>
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<varlistentry id='log-ratelimit-kmsg'>
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<term><varname>$SYSTEMD_LOG_RATELIMIT_KMSG</varname></term>
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<listitem><para id='log-ratelimit-kmsg-body'> Whether to ratelimit kmsg or not. Takes a boolean.
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Defaults to <literal>true</literal>. If disabled, systemd will not ratelimit messages written to kmsg.
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</para></listitem>
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</varlistentry>
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<varlistentry id='pager'>
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<term><varname>$SYSTEMD_PAGER</varname></term>
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<listitem><para>Pager to use when <option>--no-pager</option> is not given; overrides
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<varname>$PAGER</varname>. If neither <varname>$SYSTEMD_PAGER</varname> nor <varname>$PAGER</varname> are set, a
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set of well-known pager implementations are tried in turn, including
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<citerefentry project='man-pages'><refentrytitle>less</refentrytitle><manvolnum>1</manvolnum></citerefentry> and
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<citerefentry project='man-pages'><refentrytitle>more</refentrytitle><manvolnum>1</manvolnum></citerefentry>, until one is found. If
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no pager implementation is discovered no pager is invoked. Setting this environment variable to an empty string
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or the value <literal>cat</literal> is equivalent to passing <option>--no-pager</option>.</para>
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<para>Note: if <varname>$SYSTEMD_PAGERSECURE</varname> is not set, <varname>$SYSTEMD_PAGER</varname>
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(as well as <varname>$PAGER</varname>) will be silently ignored.</para></listitem>
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</varlistentry>
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<varlistentry id='less'>
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<term><varname>$SYSTEMD_LESS</varname></term>
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<listitem><para>Override the options passed to <command>less</command> (by default
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<literal>FRSXMK</literal>).</para>
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<para>Users might want to change two options in particular:</para>
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<variablelist>
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<varlistentry>
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<term><option>K</option></term>
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<listitem>
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<para>This option instructs the pager to exit immediately when
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<keycombo><keycap>Ctrl</keycap><keycap>C</keycap></keycombo> is pressed. To allow
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<command>less</command> to handle <keycombo><keycap>Ctrl</keycap><keycap>C</keycap></keycombo>
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itself to switch back to the pager command prompt, unset this option.</para>
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<para>If the value of <varname>$SYSTEMD_LESS</varname> does not include <literal>K</literal>,
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and the pager that is invoked is <command>less</command>,
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<keycombo><keycap>Ctrl</keycap><keycap>C</keycap></keycombo> will be ignored by the
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executable, and needs to be handled by the pager.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><option>X</option></term>
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<listitem>
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<para>This option instructs the pager to not send termcap initialization and deinitialization
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strings to the terminal. It is set by default to allow command output to remain visible in the
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terminal even after the pager exits. Nevertheless, this prevents some pager functionality from
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working, in particular paged output cannot be scrolled with the mouse.</para>
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</listitem>
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</varlistentry>
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</variablelist>
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<para>See
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<citerefentry project='man-pages'><refentrytitle>less</refentrytitle><manvolnum>1</manvolnum></citerefentry>
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for more discussion.</para></listitem>
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</varlistentry>
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<varlistentry id='lesscharset'>
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<term><varname>$SYSTEMD_LESSCHARSET</varname></term>
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<listitem><para>Override the charset passed to <command>less</command> (by default <literal>utf-8</literal>, if
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the invoking terminal is determined to be UTF-8 compatible).</para></listitem>
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</varlistentry>
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<varlistentry id='lesssecure'>
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<term><varname>$SYSTEMD_PAGERSECURE</varname></term>
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<listitem><para>Takes a boolean argument. When true, the "secure" mode of the pager is enabled; if
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false, disabled. If <varname>$SYSTEMD_PAGERSECURE</varname> is not set at all, secure mode is enabled
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if the effective UID is not the same as the owner of the login session, see
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<citerefentry project='man-pages'><refentrytitle>geteuid</refentrytitle><manvolnum>2</manvolnum></citerefentry>
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and <citerefentry><refentrytitle>sd_pid_get_owner_uid</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
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In secure mode, <option>LESSSECURE=1</option> will be set when invoking the pager, and the pager shall
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disable commands that open or create new files or start new subprocesses. When
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<varname>$SYSTEMD_PAGERSECURE</varname> is not set at all, pagers which are not known to implement
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secure mode will not be used. (Currently only
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<citerefentry project='man-pages'><refentrytitle>less</refentrytitle><manvolnum>1</manvolnum></citerefentry>
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implements secure mode.)</para>
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<para>Note: when commands are invoked with elevated privileges, for example under <citerefentry
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project='man-pages'><refentrytitle>sudo</refentrytitle><manvolnum>8</manvolnum></citerefentry> or
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<citerefentry
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project='die-net'><refentrytitle>pkexec</refentrytitle><manvolnum>1</manvolnum></citerefentry>, care
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must be taken to ensure that unintended interactive features are not enabled. "Secure" mode for the
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pager may be enabled automatically as describe above. Setting <varname>SYSTEMD_PAGERSECURE=0</varname>
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or not removing it from the inherited environment allows the user to invoke arbitrary commands. Note
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that if the <varname>$SYSTEMD_PAGER</varname> or <varname>$PAGER</varname> variables are to be
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honoured, <varname>$SYSTEMD_PAGERSECURE</varname> must be set too. It might be reasonable to completely
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disable the pager using <option>--no-pager</option> instead.</para></listitem>
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</varlistentry>
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<varlistentry id='colors'>
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<term><varname>$SYSTEMD_COLORS</varname></term>
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<listitem><para>Takes a boolean argument. When true, <command>systemd</command> and related utilities
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will use colors in their output, otherwise the output will be monochrome. Additionally, the variable can
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take one of the following special values: <literal>16</literal>, <literal>256</literal> to restrict the use
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of colors to the base 16 or 256 ANSI colors, respectively. This can be specified to override the automatic
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decision based on <varname>$TERM</varname> and what the console is connected to.</para></listitem>
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</varlistentry>
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<!-- This is not documented on purpose, because it is not clear if $NO_COLOR will become supported
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widely enough. So let's provide support, but without advertising this.
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<varlistentry id='no-color'>
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<term><varname>$NO_COLOR</varname></term>
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<listitem><para>If set (to any value), and <varname>$SYSTEMD_COLORS</varname> is not set, equivalent to
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<option>SYSTEMD_COLORS=0</option>. See <ulink url="https://no-color.org/">no-color.org</ulink>.</para>
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</listitem>
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</varlistentry>
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-->
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<varlistentry id='urlify'>
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<term><varname>$SYSTEMD_URLIFY</varname></term>
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<listitem><para>The value must be a boolean. Controls whether clickable links should be generated in
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the output for terminal emulators supporting this. This can be specified to override the decision that
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<command>systemd</command> makes based on <varname>$TERM</varname> and other conditions.</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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