<itemizedlist>

<listitem>

<para>

If you ran <command>pg_upgrade</command>

with <option>--check</option>, no modifications were made to the old

cluster and you can re-use it anytime.

If the <option>--check</option> option was used, the old cluster

was unmodified; it can be restarted.

</para>

</listitem>

<listitem>

<para>

If you ran <command>pg_upgrade</command>

with <option>--link</option>, the data files are shared between the

old and new cluster. If you started the new cluster, the new

server has written to those shared files and it is unsafe to

use the old cluster.

If the <option>--link</option> option was <emphasis>not</emphasis>

used, the old cluster was unmodified; it can be restarted.

</para>

</listitem>

<listitem>

<para>

If you ran <command>pg_upgrade</command> <emphasis>without</emphasis>

<option>--link</option> or did not start the new server, the

old cluster was not modified except that, if linking

started, a <literal>.old</literal> suffix was appended to

<filename>$PGDATA/global/pg_control</filename>. To reuse the old

cluster, possibly remove the <filename>.old</filename> suffix from

<filename>$PGDATA/global/pg_control</filename>; you can then restart the

old cluster.

If the <option>--link</option> option was used, the data

files might be shared between the old and new cluster:

<itemizedlist>

<listitem>

<para>

If <command>pg_upgrade</command> aborted before linking started,

the old cluster was unmodified; it can be restarted.

</para>

</listitem>

<listitem>

<para>

If you did <emphasis>not</emphasis> start the new cluster, the old

cluster was unmodified except that, when linking started, a

<literal>.old</literal> suffix was appended to

<filename>$PGDATA/global/pg_control</filename>. To reuse the old

cluster, remove the <filename>.old</filename> suffix from

<filename>$PGDATA/global/pg_control</filename>; you can then restart

the old cluster.

</para>

</listitem>

<listitem>

<para>

If you did start the new cluster, it has written to shared files

and it is unsafe to use the old cluster. The old cluster will

need to be restored from backup in this case.

</para>

</listitem>

</itemizedlist>

</para>

</listitem>

</itemizedlist>