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Message-ID: <f5bb021f-8f45-4825-9b4a-39241ea27a2f@jakobs.com>
Date: Wed, 12 Aug 2026 12:50:57 +0200
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To: PostgreSQL mailing list <pgsql-admin@lists.postgresql.org>
From: Holger Jakobs <holger@jakobs.com>
Subject: pg_upgrade from 17.10 to 18.4 on Ubuntu fails: Finding the real data
 directory for the target cluster sh: 1: (null)/postgres: not found
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Dear Friends,

Today a pg_upgrade failed with this awkward message:

Finding the real data directory for the source cluster        ok
Finding the real data directory for the target cluster        sh: 1: 
(null)/postgres: not found

I checked the source code of pg_upgrade.c and thus options.c and found 
that the (null) above stems from an uninitialised variable called cmd, 
declared in line 433 of option.c

Line 468 reads:

     snprintf(cmd, sizeof(cmd), "\"%s/postgres\" -D \"%s\" -C 
data_directory",
              cluster->bindir, cluster->pgconfig);

Calling the postgres binary (from the package, didn't compile myself) 
works fine and gives me the correct real data directory:

     $ /usr/lib/postgresql/18/bin/postgres -D /etc/postgresql/18/main -C 
data_directory
     /var/lib/postgresql/18/main

So how come that cmd is NULL in line 468? I actually cannot find where 
the variable was given any content, so it's NULL. This generates the 
error message with "(null)/postgres not found"

Obviously, cmd should contain the path of the oldbin directory, which is 
to be derived from the path of the pg_upgrade being called. I didn't use 
the -B option because the documentation says that it's optional and will 
use the directory of pg_upgrade.

https://www.postgresql.org/docs/current/pgupgrade.html tells me:
|   -B| /|bindir|/
|   --new-bindir=|/|bindir
|/         the new PostgreSQL executable directory; default is the 
directory where pg_upgrade resides

Obviously, this doesn't work as described.

When giving the path to the new bin directory with -B, pg_upgrade works 
fine.

Please correct the code so that cmd gets initialised or alter the 
documentation making the option -B mandatory.

Kind Regards,

Holger


-- 

Holger Jakobs, Bergisch Gladbach, Germany

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    <p>Dear Friends,</p>
    <p>Today a pg_upgrade failed with this awkward message:</p>
    <p>Finding the real data directory for the source cluster        ok<br>
      Finding the real data directory for the target cluster        sh:
      1: (null)/postgres: not found</p>
    <p>I checked the source code of pg_upgrade.c and thus options.c and
      found that the (null) above stems from an uninitialised variable
      called cmd, declared in line 433 of option.c</p>
    <p>Line 468 reads:</p>
    <p>    snprintf(cmd, sizeof(cmd), "\"%s/postgres\" -D \"%s\" -C
      data_directory",<br>
                   cluster-&gt;bindir, cluster-&gt;pgconfig);</p>
    <p>Calling the postgres binary (from the package, didn't compile
      myself) works fine and gives me the correct real data directory:</p>
    <p>    $ /usr/lib/postgresql/18/bin/postgres -D
      /etc/postgresql/18/main -C data_directory<br>
          /var/lib/postgresql/18/main<br>
    </p>
    <p>So how come that cmd is NULL in line 468? I actually cannot find
      where the variable was given any content, so it's NULL. This
      generates the error message with "(null)/postgres not found"</p>
    <p>Obviously, cmd should contain the path of the oldbin directory,
      which is to be derived from the path of the pg_upgrade being
      called. I didn't use the -B option because the documentation says
      that it's optional and will use the directory of pg_upgrade.</p>
    <a class="moz-txt-link-freetext" href="https://www.postgresql.org/docs/current/pgupgrade.html">https://www.postgresql.org/docs/current/pgupgrade.html</a> tells me:<dt><span
        class="term"><code class="option">   -B</code> <em
          class="replaceable"><code>bindir</code></em><br>
      </span><span class="term"><code class="option">   --new-bindir=</code><em
          class="replaceable"><code>bindir<br>
          </code></em></span>         the new PostgreSQL executable
      directory; default is the directory where <span
        class="application">pg_upgrade</span> resides</dt>
    <p class="moz-signature">Obviously, this doesn't work as described.</p>
    <p class="moz-signature">When giving the path to the new bin
      directory with -B, pg_upgrade works fine.</p>
    <p class="moz-signature">Please correct the code so that cmd gets
      initialised or alter the documentation making the option -B
      mandatory.</p>
    <p class="moz-signature">Kind Regards,</p>
    <p class="moz-signature">Holger</p>
    <div class="moz-signature"><br>
    </div>
    <div class="moz-signature">-- <br>
      <p>Holger Jakobs, Bergisch Gladbach, Germany</p>
    </div>
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