8000 doc: Add advice about systemd RemoveIPC · DanteG41/postgres@6a1459f · GitHub
[go: up one dir, main page]
Skip to content

Commit 6a1459f

Browse files
peterepetere
committed
doc: Add advice about systemd RemoveIPC
Reviewed-by: Magnus Hagander <magnus@hagander.net>
1 parent e6c7ff9 commit 6a1459f

File tree

1 file changed

+79
-0
lines changed

1 file changed

+79
-0
lines changed

‎doc/src/sgml/runtime.sgml

Lines changed: 79 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1162,6 +1162,85 @@ project.max-msg-ids=(priv,4096,deny)
11621162

11631163
</sect2>
11641164

1165+
<sect2 id="systemd-removeipc">
1166+
<title>systemd RemoveIPC</title>
1167+
1168+
<indexterm>
1169+
<primary>systemd</primary>
1170+
<secondary>RemoveIPC</secondary>
1171+
</indexterm>
1172+
1173+
<para>
1174+
If <productname>systemd</productname> is in use, some care must be taken
1175+
that IPC resources (shared memory and semaphores) are not prematurely
1176+
removed by the operating system. This is especially of concern when
1177+
installing PostgreSQL from source. Users of distribution packages of
1178+
PostgreSQL are less likely to be affected, as
1179+
the <literal>postgres</literal> user is then normally created as a system
1180+
user.
1181+
</para>
1182+
1183+
<para>
1184+
The setting <literal>RemoveIPC</literal>
1185+
in <filename>logind.conf</filename> controls whether IPC objects are
1186+
removed when a user fully logs out. System users are exempt. This
1187+
setting defaults to on in stock <productname>systemd</productname>, but
1188+
some operating system distributions default it to off.
1189+
</para>
1190+
1191+
<para>
1192+
A typical observed effect when this setting is on is that the semaphore
1193+
objects used by a PostgreSQL server are removed at apparently random
1194+
times, leading to the server crashing with log messages like
1195+
<screen>
1196+
LOG: semctl(1234567890, 0, IPC_RMID, ...) failed: Invalid argument
1197+
</screen>
1198+
Different types of IPC objects (shared memory vs. semaphores, System V
1199+
vs. POSIX) are treated slightly differently
1200+
by <productname>systemd</productname>, so one might observe that some IPC
1201+
resources are not removed in the same way as others. But it is not
1202+
advisable to rely on these subtle differences.
1203+
</para>
1204+
1205+
<para>
1206+
A <quote>user logging out</quote> might happen as part of a maintenance
1207+
job or manually when an administrator logs in as
1208+
the <literal>postgres</literal> user or something similar, so it is hard
1209+
to prevent in general.
1210+
</para>
1211+
1212+
<para>
1213+
What is a <quote>system user</quote> is determined
1214+
at <productname>systemd</productname> compile time from
1215+
the <symbol>SYS_UID_MAX</symbol> setting
1216+
in <filename>/etc/login.defs</filename>.
1217+
</para>
1218+
1219+
<para>
1220+
Packaging and deployment scripts should be careful to create
1221+
the <literal>postgres</literal> user as a system user by
1222+
using <literal>useradd -r</literal>, <literal>adduser --system</literal>,
1223+
or equivalent.
1224+
</para>
1225+
1226+
<para>
1227+
Alternatively, if the user account was created incorrectly or cannot be
1228+
changed, it is recommended to set
1229+
<programlisting>
1230+
RemoveIPC=no
1231+
</programlisting>
1232+
in <filename>/etc/systemd/logind.conf</filename> or another appropriate
1233+
configuration file.
1234+
</para>
1235+
1236+
<caution>
1237+
<para>
1238+
At least one of these two things has to be ensured, or the PostgreSQL
1239+
server will be very unreliable.
1240+
</para>
1241+
</caution>
1242+
</sect2>
1243+
11651244
<sect2>
11661245
<title>Resource Limits</title>
11671246

0 commit comments

Comments
 (0)
0