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man: document footgun on SocketUser= #32503

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man: document footgun on SocketUser= #32503

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7 changes: 6 additions & 1 deletion man/systemd.socket.xml
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Original file line number Diff line number Diff line change
Expand Up @@ -377,7 +377,12 @@
sockets and FIFO nodes in the file system are owned by the specified user and group. If unset (the
default), the nodes are owned by the root user/group (if run in system context) or the invoking
user/group (if run in user context). If only a user is specified but no group, then the group is
derived from the user's default group.</para>
derived from the user's default group.
Note that this might not have the desired effect if a socket happens to be inside a directory also
referred to in a <varname>RuntimeDirectory=</varname>, <varname>StateDirectory=</varname>,
<varname>CacheDirectory=</varname>, or <varname>LogsDirectory=</varname> of any service, due to the
change of ownership caused by these options.
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I am not following? What's the problem?

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As in the issue description, SocketUser= is used to make the socket file owned by a different user than the service. If you however also have RuntimeDirectory= set, and your socket file is in there, both places try to chown this.

The common example for breakage is myservice wanting a /run/myservice/sock to be owned by otheruser.

If myservice also sets RuntimeDirectory=myservice, which chowns to myservice user, these two things race.

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RuntimeDIrectory= doing the chown is well-documented, but people using SocketUser= might not be aware of this conflicting. Hence the pointer.

</para>

<xi:include href="version-info.xml" xpointer="v214"/></listitem>
</varlistentry>
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