81 lines
5.4 KiB
Diff
81 lines
5.4 KiB
Diff
From f6b09a2ed646f0a0b54605d4c19a898ab2bbf192 Mon Sep 17 00:00:00 2001
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From: Lennart Poettering <lennart@poettering.net>
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Date: Mon, 18 Sep 2023 17:51:49 +0200
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Subject: [PATCH 2/3] man: document the new
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PollLimitIntervalSec=/PollLimitBurst= settings
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(cherry picked from commit 9373fce68de183a615d44fe100dcf22e3c9b8c3e)
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---
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man/systemd.socket.xml | 58 ++++++++++++++++++++++++++++++++++--------
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1 file changed, 47 insertions(+), 11 deletions(-)
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diff --git a/man/systemd.socket.xml b/man/systemd.socket.xml
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index 45555302f1..462978d438 100644
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--- a/man/systemd.socket.xml
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+++ b/man/systemd.socket.xml
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@@ -830,17 +830,53 @@
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<term><varname>TriggerLimitIntervalSec=</varname></term>
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<term><varname>TriggerLimitBurst=</varname></term>
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- <listitem><para>Configures a limit on how often this socket unit may be activated within a specific time
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- interval. The <varname>TriggerLimitIntervalSec=</varname> may be used to configure the length of the time
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- interval in the usual time units <literal>us</literal>, <literal>ms</literal>, <literal>s</literal>,
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- <literal>min</literal>, <literal>h</literal>, … and defaults to 2s (See
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- <citerefentry><refentrytitle>systemd.time</refentrytitle><manvolnum>7</manvolnum></citerefentry> for details on
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- the various time units understood). The <varname>TriggerLimitBurst=</varname> setting takes a positive integer
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- value and specifies the number of permitted activations per time interval, and defaults to 200 for
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- <varname>Accept=yes</varname> sockets (thus by default permitting 200 activations per 2s), and 20 otherwise (20
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- activations per 2s). Set either to 0 to disable any form of trigger rate limiting. If the limit is hit, the
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- socket unit is placed into a failure mode, and will not be connectible anymore until restarted. Note that this
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- limit is enforced before the service activation is enqueued.</para></listitem>
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+ <listitem><para>Configures a limit on how often this socket unit may be activated within a specific
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+ time interval. The <varname>TriggerLimitIntervalSec=</varname> setting may be used to configure the
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+ length of the time interval in the usual time units <literal>us</literal>, <literal>ms</literal>,
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+ <literal>s</literal>, <literal>min</literal>, <literal>h</literal>, … and defaults to 2s (See
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+ <citerefentry><refentrytitle>systemd.time</refentrytitle><manvolnum>7</manvolnum></citerefentry> for
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+ details on the various time units understood). The <varname>TriggerLimitBurst=</varname> setting
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+ takes a positive integer value and specifies the number of permitted activations per time interval,
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+ and defaults to 200 for <varname>Accept=yes</varname> sockets (thus by default permitting 200
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+ activations per 2s), and 20 otherwise (20 activations per 2s). Set either to 0 to disable any form of
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+ trigger rate limiting.</para>
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+
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+ <para>If the limit is hit, the socket unit is placed into a failure mode, and will not be connectible
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+ anymore until restarted. Note that this limit is enforced before the service activation is
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+ enqueued.</para>
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+
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+ <para>Compare with <varname>PollLimitIntervalSec=</varname>/<varname>PollLimitBurst=</varname>
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+ described below, which implements a temporary slowdown if a socket unit is flooded with incoming
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+ traffic, as opposed to the permanent failure state
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+ <varname>TriggerLimitIntervalSec=</varname>/<varname>TriggerLimitBurst=</varname> results in.</para>
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+ </listitem>
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+ </varlistentry>
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+
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+ <varlistentry>
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+ <term><varname>PollLimitIntervalSec=</varname></term>
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+ <term><varname>PollLimitBurst=</varname></term>
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+
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+ <listitem><para>Configures a limit on how often polling events on the file descriptors backing this
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+ socket unit will be considered. This pair of settings is similar to
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+ <varname>TriggerLimitIntervalSec=</varname>/<varname>TriggerLimitBurst=</varname> but instead of
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+ putting a (fatal) limit on the activation frequency puts a (transient) limit on the polling
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+ frequency. The expected parameter syntax and range are identical to that of the aforementioned
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+ options, and can be disabled the same way.</para>
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+
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+ <para>If the polling limit is hit polling is temporarily disabled on it until the specified time
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+ window passes. The polling limit hence slows down connection attempts if hit, but unlike the trigger
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+ limit won't cause permanent failures. It's the recommended mechanism to deal with DoS attempts
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+ through packet flooding.</para>
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+
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+ <para>The polling limit is enforced per file descriptor to listen on, as opposed to the trigger limit
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+ which is enforced for the entire socket unit. This distinction matters for socket units that listen
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+ on multiple file descriptors (i.e. have multiple <varname>ListenXYZ=</varname> stanzas).</para>
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+
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+ <para>These setting defaults to 150 (in case of <varname>Accept=yes</varname>) and 15 (otherwise)
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+ polling events per 2s. This is considerably lower than the default values for the trigger limit (see
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+ above) and means that the polling limit should typically ensure the trigger limit is never hit,
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+ unless one of them is reconfigured or disabled.</para>
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+ </listitem>
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</varlistentry>
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</variablelist>
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