man/less-variables.xml

   1 <?xml version="1.0"?>
   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
   3   "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd">
   4 <!-- SPDX-License-Identifier: LGPL-2.1+ -->
   5
   6 <refsect1>
   7   <title>Environment</title>
   8
   9   <variablelist class='environment-variables'>
  10     <varlistentry id='pager'>
  11       <term><varname>$SYSTEMD_PAGER</varname></term>
  12
  13       <listitem><para>Pager to use when <option>--no-pager</option> is not given; overrides
  14       <varname>$PAGER</varname>. If neither <varname>$SYSTEMD_PAGER</varname> nor <varname>$PAGER</varname> are set, a
  15       set of well-known pager implementations are tried in turn, including
  16       <citerefentry project='man-pages'><refentrytitle>less</refentrytitle><manvolnum>1</manvolnum></citerefentry> and
  17       <citerefentry project='man-pages'><refentrytitle>more</refentrytitle><manvolnum>1</manvolnum></citerefentry>, until one is found. If
  18       no pager implementation is discovered no pager is invoked. Setting this environment variable to an empty string
  19       or the value <literal>cat</literal> is equivalent to passing <option>--no-pager</option>.</para></listitem>
  20     </varlistentry>
  21
  22     <varlistentry id='less'>
  23       <term><varname>$SYSTEMD_LESS</varname></term>
  24
  25       <listitem><para>Override the options passed to <command>less</command> (by default
  26       <literal>FRSXMK</literal>).</para>
  27
  28       <para>Users might want to change two options in particular:</para>
  29
  30       <variablelist>
  31         <varlistentry>
  32           <term><option>K</option></term>
  33
  34           <para>This option instructs the pager to exit immediately when
  35           <keycombo><keycap>Ctrl</keycap><keycap>C</keycap></keycombo> is pressed. To allow
  36           <command>less</command> to handle <keycombo><keycap>Ctrl</keycap><keycap>C</keycap></keycombo>
  37           itself to switch back to the pager command prompt, unset this option.</para>
  38
  39           <para>If the value of <varname>$SYSTEMD_LESS</varname> does not include <literal>K</literal>,
  40           and the pager that is invoked is <command>less</command>,
  41           <keycombo><keycap>Ctrl</keycap><keycap>C</keycap></keycombo> will be ignored by the
  42           executable, and needs to be handled by the pager.</para>
  43         </varlistentry>
  44
  45         <varlistentry>
  46           <term><option>X</option></term>
  47
  48           <para>This option instructs the pager to not send termcap initialization and deinitialization
  49           strings to the terminal. It is set by default to allow command output to remain visible in the
  50           terminal even after the pager exits. Nevertheless, this prevents some pager functionality from
  51           working, in particular paged output cannot be scrolled with the mouse.</para>
  52         </varlistentry>
  53       </variablelist>
  54
  55       <para>See
  56       <citerefentry project='man-pages'><refentrytitle>less</refentrytitle><manvolnum>1</manvolnum></citerefentry>
  57       for more discussion.</para></listitem>
  58     </varlistentry>
  59
  60     <varlistentry id='lesscharset'>
  61       <term><varname>$SYSTEMD_LESSCHARSET</varname></term>
  62
  63       <listitem><para>Override the charset passed to <command>less</command> (by default <literal>utf-8</literal>, if
  64       the invoking terminal is determined to be UTF-8 compatible).</para></listitem>
  65     </varlistentry>
  66
  67     <varlistentry id='lesssecure'>
  68       <term><varname>$SYSTEMD_PAGERSECURE</varname></term>
  69
  70       <listitem><para>Takes a boolean argument. When true, the "secure" mode of the pager is enabled; if
  71       false, disabled. If <varname>$SYSTEMD_PAGERSECURE</varname> is not set at all, secure mode is enabled
  72       if the effective UID is not the same as the owner of the login session, see <citerefentry
  73       project='man-pages'><refentrytitle>geteuid</refentrytitle><manvolnum>2</manvolnum></citerefentry> and
  74       <citerefentry><refentrytitle>sd_pid_get_owner_uid</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
  75       In secure mode, <option>LESSSECURE=1</option> will be set when invoking the pager, and the pager shall
  76       disable commands that open or create new files or start new subprocesses. When
  77       <varname>$SYSTEMD_PAGERSECURE</varname> is not set at all, pagers which are not known to implement
  78       secure mode will not be used. (Currently only
  79       <citerefentry><refentrytitle>less</refentrytitle><manvolnum>1</manvolnum></citerefentry> implements
  80       secure mode.)</para>
  81
  82       <para>Note: when commands are invoked with elevated privileges, for example under <citerefentry
  83       project='man-pages'><refentrytitle>sudo</refentrytitle><manvolnum>8</manvolnum></citerefentry> or
  84       <citerefentry
  85       project='die-net'><refentrytitle>pkexec</refentrytitle><manvolnum>1</manvolnum></citerefentry>, care
  86       must be taken to ensure that unintended interactive features are not enabled. "Secure" mode for the
  87       pager may be enabled automatically as describe above. Setting <varname>SYSTEMD_PAGERSECURE=0</varname>
  88       or not removing it from the inherited environment allows the user to invoke arbitrary commands. Note
  89       that if the <varname>$SYSTEMD_PAGER</varname> or <varname>$PAGER</varname> variables are to be
  90       honoured, <varname>$SYSTEMD_PAGERSECURE</varname> must be set too. It might be reasonable to completly
  91       disable the pager using <option>--no-pager</option> instead.</para></listitem>
  92     </varlistentry>
  93
  94     <varlistentry id='colors'>
  95       <term><varname>$SYSTEMD_COLORS</varname></term>
  96
  97       <listitem><para>The value must be a boolean. Controls whether colorized output should be
  98       generated. This can be specified to override the decision that <command>systemd</command> makes based
  99       on <varname>$TERM</varname> and what the console is connected to.</para>
 100       </listitem>
 101     </varlistentry>
 102
 103     <!-- This is not documented on purpose, because it is not clear if $NO_COLOR will become supported
 104          widely enough. So let's provide support, but without advertising this.
 105     <varlistentry id='no-color'>
 106       <term><varname>$NO_COLOR</varname></term>
 107
 108       <listitem><para>If set (to any value), and <varname>$SYSTEMD_COLORS</varname> is not set, equivalent to
 109       <option>SYSTEMD_COLORS=0</option>. See <ulink url="https://no-color.org/">no-color.org</ulink>.</para>
 110       </listitem>
 111     </varlistentry>
 112     -->
 113
 114     <varlistentry id='urlify'>
 115       <term><varname>$SYSTEMD_URLIFY</varname></term>
 116
 117       <listitem><para>The value must be a boolean. Controls whether clickable links should be generated in
 118       the output for terminal emulators supporting this. This can be specified to override the decision that
 119       <command>systemd</command> makes based on <varname>$TERM</varname> and other conditions.</para>
 120       </listitem>
 121     </varlistentry>
 122
 123   </variablelist>
 124 </refsect1>