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-rw-r--r--man/machinectl.xml45
1 files changed, 36 insertions, 9 deletions
diff --git a/man/machinectl.xml b/man/machinectl.xml
index b50f03f36f..55bb694e6c 100644
--- a/man/machinectl.xml
+++ b/man/machinectl.xml
@@ -508,16 +508,32 @@
<term><command>set-limit</command> [<replaceable>NAME</replaceable>] <replaceable>BYTES</replaceable></term>
<listitem><para>Sets the maximum size in bytes a specific
- container or VM image, or all images may grow up to
- (quota). Takes either one or two parameters. The first,
+ container or VM image, or all images may grow up to on disk
+ (disk quota). Takes either one or two parameters. The first,
optional parameter refers to a container or VM image name. If
- specified the size limit of the specified images is
- changed. If omitted the overall size limit of the sum of all
- images stored locally is changed. The final argument specifies
- the size limit in bytes, possibly suffixed by the usual K, M,
- G, T units. If the size limit shall be disabled, specify
- <literal>-</literal> as size. This operation is currently only
- supported on btrfs subvolume images.</para></listitem>
+ specified the size limit of the specified image is changed. If
+ omitted the overall size limit of the sum of all images stored
+ locally is changed. The final argument specifies the size
+ limit in bytes, possibly suffixed by the usual K, M, G, T
+ units. If the size limit shall be disabled, specify
+ <literal>-</literal> as size.</para>
+
+ <para>Note that per-container size limits are only supported
+ on btrfs file systems. Also note that if
+ <command>set-limit</command> is invoked without image
+ parameter, and <filename>/var/lib/machines</filename> is
+ empty, and the directory is not located on btrfs, a btrfs
+ loopback file is implicitly created as
+ <filename>/var/lib/machines.raw</filename> with the given
+ size, and mounted to
+ <filename>/var/lib/machines</filename>. The size of the
+ loopback may later be readjusted with
+ <command>set-limit</command>, as well. If such a
+ loopback-mounted <filename>/var/lib/machines</filename>
+ directory is used <command>set-limit</command> without image
+ name alters both the quota setting within the file system as
+ well as the loopback file and file system size
+ itself.</para></listitem>
</varlistentry>
</variablelist></refsect2>
@@ -686,6 +702,17 @@
<filename>/var/lib/machines/</filename> to make them available for
control with <command>machinectl</command>.</para>
+ <para>Note that many image operations are only supported,
+ efficient or atomic on btrfs file systems. Due to this, if the
+ <command>pull-tar</command>, <command>pull-raw</command>,
+ <command>pull-dkr</command> and <command>set-limit</command>
+ commands notice that <filename>/var/lib/machines</filename> is
+ empty and not located on btrfs, they will implicitly set up a
+ loopback file <filename>/var/lib/machines.raw</filename>
+ containing a btrfs file system that is mounted to
+ <filename>/var/lib/machines</filename>. The size of this loopback
+ file may be controlled dynamically with <command>set-limit</command>.</para>
+
<para>Disk images are understood by
<citerefentry><refentrytitle>systemd-nspawn</refentrytitle><manvolnum>1</manvolnum></citerefentry>
and <command>machinectl</command> in three formats:</para>