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c4fea19abb
This commit extends $SYSTEMD_COLORS to an enum variable (compared to a simple boolean) which specifies the "colors mode". This means that, in addition to disabling colors altogether, it's now possible to restrict the console output to 16 or 256 colors only.
126 lines
6.9 KiB
XML
126 lines
6.9 KiB
XML
<?xml version="1.0"?>
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd">
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<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
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<refsect1>
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<title>Environment</title>
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<variablelist class='environment-variables'>
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<varlistentry id='pager'>
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<term><varname>$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>$PAGER</varname> are set, a
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set of well-known pager implementations are tried in turn, including
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<citerefentry project='man-pages'><refentrytitle>less</refentrytitle><manvolnum>1</manvolnum></citerefentry> and
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<citerefentry project='man-pages'><refentrytitle>more</refentrytitle><manvolnum>1</manvolnum></citerefentry>, until one is found. If
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no pager implementation is discovered no pager is invoked. Setting this environment variable to an empty string
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or the value <literal>cat</literal> is equivalent to passing <option>--no-pager</option>.</para></listitem>
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</varlistentry>
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<varlistentry id='less'>
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<term><varname>$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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<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>$SYSTEMD_LESS</varname> does not include <literal>K</literal>,
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and the pager that is invoked is <command>less</command>,
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<keycombo><keycap>Ctrl</keycap><keycap>C</keycap></keycombo> will be ignored by the
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executable, and needs to be handled by the pager.</para>
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</varlistentry>
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<varlistentry>
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<term><option>X</option></term>
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<para>This option instructs the pager to not send termcap initialization and deinitialization
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strings to the terminal. It is set by default to allow command output to remain visible in the
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terminal even after the pager exits. Nevertheless, this prevents some pager functionality from
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working, in particular paged output cannot be scrolled with the mouse.</para>
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</varlistentry>
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</variablelist>
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<para>See
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<citerefentry project='man-pages'><refentrytitle>less</refentrytitle><manvolnum>1</manvolnum></citerefentry>
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for more discussion.</para></listitem>
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</varlistentry>
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<varlistentry id='lesscharset'>
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<term><varname>$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 <citerefentry
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project='man-pages'><refentrytitle>geteuid</refentrytitle><manvolnum>2</manvolnum></citerefentry> and
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<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>$SYSTEMD_PAGERSECURE</varname> is not set at all, pagers which are not known to implement
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secure mode will not be used. (Currently only
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<citerefentry><refentrytitle>less</refentrytitle><manvolnum>1</manvolnum></citerefentry> implements
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secure mode.)</para>
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<para>Note: when commands are invoked with elevated privileges, for example under <citerefentry
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project='man-pages'><refentrytitle>sudo</refentrytitle><manvolnum>8</manvolnum></citerefentry> or
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<citerefentry
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project='die-net'><refentrytitle>pkexec</refentrytitle><manvolnum>1</manvolnum></citerefentry>, care
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must be taken to ensure that unintended interactive features are not enabled. "Secure" mode for the
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pager may be enabled automatically as describe above. Setting <varname>SYSTEMD_PAGERSECURE=0</varname>
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or not removing it from the inherited environment allows the user to invoke arbitrary commands. Note
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that if the <varname>$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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