title: Problem getting php7.4-fpm to start on ubuntu
body: <p>I am using nginx, and not apache. Just upgraded from 18.04 to 20.04 and thus php7.2 to php7.4.
  However php7.4-fpm fails to start. This is my log.</p>
  <pre><code>ian@thebeb:/etc/php/7.4/fpm$ sudo /etc/init.d/php7.4-fpm restart
  Restarting php7.4-fpm (via systemctl): php7.4-fpm.serviceJob for php7.4-fpm.service failed because the control process exited with error code.
  See &quot;systemctl status php7.4-fpm.service&quot; and &quot;journalctl -xe&quot; for details.
   failed!
  ian@thebeb:/etc/php/7.4/fpm$ systemctl status php7.4-fpm.service
  ● php7.4-fpm.service - The PHP 7.4 FastCGI Process Manager
       Loaded: loaded (/lib/systemd/system/php7.4-fpm.service; enabled; vendor preset: enabled)
       Active: failed (Result: exit-code) since Sun 2021-01-17 21:01:20 GMT; 9s ago
         Docs: man:php-fpm7.4(8)
      Process: 63191 ExecStart=/usr/sbin/php-fpm7.4 --nodaemonize --fpm-config /etc/php/7.4/fpm/php-fpm.conf (code=exited, status=127)
      Process: 63205 ExecStopPost=/usr/lib/php/php-fpm-socket-helper remove /run/php/php-fpm.sock /etc/php/7.4/fpm/pool.d/www.conf 74 (code=exited, status=0/SUCCESS)
     Main PID: 63191 (code=exited, status=127)
  
  Jan 17 21:01:20 thebeb systemd[1]: Starting The PHP 7.4 FastCGI Process Manager...
  Jan 17 21:01:20 thebeb php-fpm7.4[63191]: /usr/sbin/php-fpm7.4: symbol lookup error: /usr/sbin/php-fpm7.4: undefined symbol: pcre2_set_depth_limit_8
  Jan 17 21:01:20 thebeb systemd[1]: php7.4-fpm.service: Main process exited, code=exited, status=127/n/a
  Jan 17 21:01:20 thebeb systemd[1]: php7.4-fpm.service: Failed with result 'exit-code'.
  Jan 17 21:01:20 thebeb systemd[1]: Failed to start The PHP 7.4 FastCGI Process Manager.
  ian@thebeb:/etc/php/7.4/fpm$ journalctl -xe
  -- A start job for unit UNIT has begun execution.
  -- 
  -- The job identifier is 431.
  Jan 17 21:01:10 thebeb dbus-daemon[3745]: [session uid=1000 pid=3745] Activating via systemd: service name='org.freedesktop.Tracker1' unit='tracker-store.service' requested by ':1.2' (uid=1000 pid=3742 &gt;
  Jan 17 21:01:10 thebeb dbus-daemon[3745]: [session uid=1000 pid=3745] Successfully activated service 'org.freedesktop.Tracker1'
  Jan 17 21:01:10 thebeb systemd[3723]: Started Tracker metadata database store and lookup manager.
  -- Subject: A start job for unit UNIT has finished successfully
  -- Defined-By: systemd
  -- Support: http://www.ubuntu.com/support
  -- 
  -- A start job for unit UNIT has finished successfully.
  -- 
  -- The job identifier is 431.
  Jan 17 21:01:15 thebeb kernel: [UFW BLOCK] IN=enp0s3 OUT= MAC=01:00:5e:00:00:01:bc:14:01:0f:f6:e6:08:00 SRC=192.168.0.1 DST=224.0.0.1 LEN=36 TOS=0x00 PREC=0xC0 TTL=1 ID=0 DF PROTO=2 
  Jan 17 21:01:20 thebeb sudo[63180]:      ian : TTY=pts/1 ; PWD=/etc/php/7.4/fpm ; USER=root ; COMMAND=/etc/init.d/php7.4-fpm restart
  Jan 17 21:01:20 thebeb sudo[63180]: pam_unix(sudo:session): session opened for user root by (uid=0)
  Jan 17 21:01:20 thebeb systemd[1]: Starting The PHP 7.4 FastCGI Process Manager...
  -- Subject: A start job for unit php7.4-fpm.service has begun execution
  -- Defined-By: systemd
  -- Support: http://www.ubuntu.com/support
  -- 
  -- A start job for unit php7.4-fpm.service has begun execution.
  -- 
  -- The job identifier is 3745.
  Jan 17 21:01:20 thebeb php-fpm7.4[63191]: /usr/sbin/php-fpm7.4: symbol lookup error: /usr/sbin/php-fpm7.4: undefined symbol: pcre2_set_depth_limit_8
  Jan 17 21:01:20 thebeb systemd[1]: php7.4-fpm.service: Main process exited, code=exited, status=127/n/a
  -- Subject: Unit process exited
  -- Defined-By: systemd
  -- Support: http://www.ubuntu.com/support
  -- 
  -- An ExecStart= process belonging to unit php7.4-fpm.service has exited.
  -- 
  -- The process' exit code is 'exited' and its exit status is 127.
  Jan 17 21:01:20 thebeb systemd[1]: php7.4-fpm.service: Failed with result 'exit-code'.
  -- Subject: Unit failed
  -- Defined-By: systemd
  -- Support: http://www.ubuntu.com/support
  -- 
  -- The unit php7.4-fpm.service has entered the 'failed' state with result 'exit-code'.
  Jan 17 21:01:20 thebeb systemd[1]: Failed to start The PHP 7.4 FastCGI Process Manager.
  -- Subject: A start job for unit php7.4-fpm.service has failed
  -- Defined-By: systemd
  -- Support: http://www.ubuntu.com/support
  -- 
  -- A start job for unit php7.4-fpm.service has finished with a failure.
  -- 
  -- The job identifier is 3745 and the job result is failed.
  Jan 17 21:01:20 thebeb sudo[63180]: pam_unix(sudo:session): session closed for user root
  Jan 17 21:01:41 thebeb tracker-store[63047]: OK
  Jan 17 21:01:41 thebeb systemd[3723]: tracker-store.service: Succeeded.
  -- Subject: Unit succeeded
  -- Defined-By: systemd
  -- Support: http://www.ubuntu.com/support
  -- 
  -- The unit UNIT has successfully entered the 'dead' state.
  ian@thebeb:/etc/php/7.4/fpm$
  </code></pre>
  <p>The symbol lookup error, was symbol lookup error: /usr/sbin/php-fpm7.4: undefined symbol: pcre2_set_depth_limit_8.</p>
  <p>I have checked everything I can think of, and can't spot the problem. Now I am out of my depth! Help.</p>
  <p>Added after request:</p>
  <pre><code>ian@thebeb:/etc/php/7.4/fpm$ ldd $(which php-fpm7.4)
      linux-vdso.so.1 (0x00007ffefb4e7000)
      libargon2.so.1 =&gt; /usr/lib/x86_64-linux-gnu/libargon2.so.1 (0x00007f13e38a6000)
      libresolv.so.2 =&gt; /lib/x86_64-linux-gnu/libresolv.so.2 (0x00007f13e388a000)
      libm.so.6 =&gt; /lib/x86_64-linux-gnu/libm.so.6 (0x00007f13e373b000)
      libdl.so.2 =&gt; /lib/x86_64-linux-gnu/libdl.so.2 (0x00007f13e3735000)
      libapparmor.so.1 =&gt; /usr/lib/x86_64-linux-gnu/libapparmor.so.1 (0x00007f13e3720000)
      libsystemd.so.0 =&gt; /lib/x86_64-linux-gnu/libsystemd.so.0 (0x00007f13e3671000)
      libxml2.so.2 =&gt; /usr/lib/x86_64-linux-gnu/libxml2.so.2 (0x00007f13e34b5000)
      libssl.so.1.1 =&gt; /usr/local/lib/libssl.so.1.1 (0x00007f13e3422000)
      libcrypto.so.1.1 =&gt; /usr/local/lib/libcrypto.so.1.1 (0x00007f13e2f57000)
      libpcre2-8.so.0 =&gt; /usr/local/lib/libpcre2-8.so.0 (0x00007f13e2d0c000)
      libz.so.1 =&gt; /usr/local/lib/libz.so.1 (0x00007f13e2af0000)
      libsodium.so.23 =&gt; /usr/lib/x86_64-linux-gnu/libsodium.so.23 (0x00007f13e2a98000)
      libc.so.6 =&gt; /lib/x86_64-linux-gnu/libc.so.6 (0x00007f13e28a4000)
      libpthread.so.0 =&gt; /lib/x86_64-linux-gnu/libpthread.so.0 (0x00007f13e2881000)
      /lib64/ld-linux-x86-64.so.2 (0x00007f13e3d6f000)
      librt.so.1 =&gt; /lib/x86_64-linux-gnu/librt.so.1 (0x00007f13e2876000)
      liblzma.so.5 =&gt; /lib/x86_64-linux-gnu/liblzma.so.5 (0x00007f13e284d000)
      liblz4.so.1 =&gt; /usr/lib/x86_64-linux-gnu/liblz4.so.1 (0x00007f13e282c000)
      libgcrypt.so.20 =&gt; /usr/lib/x86_64-linux-gnu/libgcrypt.so.20 (0x00007f13e270e000)
      libicuuc.so.66 =&gt; /usr/lib/x86_64-linux-gnu/libicuuc.so.66 (0x00007f13e2526000)
      libgpg-error.so.0 =&gt; /lib/x86_64-linux-gnu/libgpg-error.so.0 (0x00007f13e2503000)
      libicudata.so.66 =&gt; /usr/lib/x86_64-linux-gnu/libicudata.so.66 (0x00007f13e0a42000)
      libstdc++.so.6 =&gt; /usr/lib/x86_64-linux-gnu/libstdc++.so.6 (0x00007f13e0861000)
      libgcc_s.so.1 =&gt; /lib/x86_64-linux-gnu/libgcc_s.so.1 (0x00007f13e0846000)
  ian@thebeb:/etc/php/7.4/fpm$ 
  </code></pre>