From: Lennart Poettering <lennart@poettering.net>
Date: Mon, 29 Jul 2019 07:24:09 +0000 (+0200)
Subject: man: document the kernel command line options to use when logging to kmsg
X-Git-Tag: v243-rc1~22
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=77ce88c1286311e6f190f76c9d5cd6beff223989;p=thirdparty%2Fsystemd.git

man: document the kernel command line options to use when logging to kmsg

Prompted by:

https://lists.freedesktop.org/archives/systemd-devel/2019-July/043149.html
---

diff --git a/man/journald.conf.xml b/man/journald.conf.xml
index 57c22565677..44fd0d2f3d7 100644
--- a/man/journald.conf.xml
+++ b/man/journald.conf.xml
@@ -288,21 +288,25 @@
         <term><varname>ForwardToConsole=</varname></term>
         <term><varname>ForwardToWall=</varname></term>
 
-        <listitem><para>Control whether log messages received by the journal daemon shall
-        be forwarded to a traditional syslog daemon, to the kernel log buffer (kmsg), to
-        the system console, or sent as wall messages to all logged-in users.  These
-        options take boolean arguments. If forwarding to syslog is enabled but nothing
-        reads messages from the socket, forwarding to syslog has no effect. By default,
-        only forwarding to wall is enabled. These settings may be overridden at boot time
-        with the kernel command line options
-        <literal>systemd.journald.forward_to_syslog</literal>,
+        <listitem><para>Control whether log messages received by the journal daemon shall be forwarded to a
+        traditional syslog daemon, to the kernel log buffer (kmsg), to the system console, or sent as wall
+        messages to all logged-in users.  These options take boolean arguments. If forwarding to syslog is
+        enabled but nothing reads messages from the socket, forwarding to syslog has no effect. By default,
+        only forwarding to wall is enabled. These settings may be overridden at boot time with the kernel
+        command line options <literal>systemd.journald.forward_to_syslog</literal>,
         <literal>systemd.journald.forward_to_kmsg</literal>,
         <literal>systemd.journald.forward_to_console</literal>, and
-        <literal>systemd.journald.forward_to_wall</literal>. If the option name is
-        specified without <literal>=</literal> and the following argument, true is
-        assumed. Otherwise, the argument is parsed as a boolean. When forwarding to the
-        console, the TTY to log to can be changed with <varname>TTYPath=</varname>,
-        described below.</para></listitem>
+        <literal>systemd.journald.forward_to_wall</literal>. If the option name is specified without
+        <literal>=</literal> and the following argument, true is assumed. Otherwise, the argument is parsed
+        as a boolean.</para>
+
+        <para>When forwarding to the console, the TTY to log to can be changed with
+        <varname>TTYPath=</varname>, described below.</para>
+
+        <para>When forwarding to the kernel log buffer (kmsg), make sure to select a suitably large size for
+        the log buffer, and ensure the kernel's rate-limiting applied to userspace processes is turned
+        off. Specifically, add <literal>log_buf_len=8M</literal> and <literal>printk.devkmsg=on</literal> (or
+        similar) to the kernel command line.</para></listitem>
       </varlistentry>
 
       <varlistentry>