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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
This commit is contained in:
Lennart Poettering 2019-07-29 09:24:09 +02:00 committed by Zbigniew Jędrzejewski-Szmek
parent 08b5953997
commit 77ce88c128

View File

@ -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>