Problem getting php7.4-fpm to start on ubuntu

Question

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.

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 "systemctl status php7.4-fpm.service" and "journalctl -xe" 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 >
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$

The symbol lookup error, was symbol lookup error: /usr/sbin/php-fpm7.4: undefined symbol: pcre2_set_depth_limit_8.

I have checked everything I can think of, and can't spot the problem. Now I am out of my depth. Help.

Added after request:

ian@thebeb:/etc/php/7.4/fpm$ ldd $(which php-fpm7.4)
    linux-vdso.so.1 (0x00007ffefb4e7000)
    libargon2.so.1 => /usr/lib/x86_64-linux-gnu/libargon2.so.1 (0x00007f13e38a6000)
    libresolv.so.2 => /lib/x86_64-linux-gnu/libresolv.so.2 (0x00007f13e388a000)
    libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007f13e373b000)
    libdl.so.2 => /lib/x86_64-linux-gnu/libdl.so.2 (0x00007f13e3735000)
    libapparmor.so.1 => /usr/lib/x86_64-linux-gnu/libapparmor.so.1 (0x00007f13e3720000)
    libsystemd.so.0 => /lib/x86_64-linux-gnu/libsystemd.so.0 (0x00007f13e3671000)
    libxml2.so.2 => /usr/lib/x86_64-linux-gnu/libxml2.so.2 (0x00007f13e34b5000)
    libssl.so.1.1 => /usr/local/lib/libssl.so.1.1 (0x00007f13e3422000)
    libcrypto.so.1.1 => /usr/local/lib/libcrypto.so.1.1 (0x00007f13e2f57000)
    libpcre2-8.so.0 => /usr/local/lib/libpcre2-8.so.0 (0x00007f13e2d0c000)
    libz.so.1 => /usr/local/lib/libz.so.1 (0x00007f13e2af0000)
    libsodium.so.23 => /usr/lib/x86_64-linux-gnu/libsodium.so.23 (0x00007f13e2a98000)
    libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f13e28a4000)
    libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0 (0x00007f13e2881000)
    /lib64/ld-linux-x86-64.so.2 (0x00007f13e3d6f000)
    librt.so.1 => /lib/x86_64-linux-gnu/librt.so.1 (0x00007f13e2876000)
    liblzma.so.5 => /lib/x86_64-linux-gnu/liblzma.so.5 (0x00007f13e284d000)
    liblz4.so.1 => /usr/lib/x86_64-linux-gnu/liblz4.so.1 (0x00007f13e282c000)
    libgcrypt.so.20 => /usr/lib/x86_64-linux-gnu/libgcrypt.so.20 (0x00007f13e270e000)
    libicuuc.so.66 => /usr/lib/x86_64-linux-gnu/libicuuc.so.66 (0x00007f13e2526000)
    libgpg-error.so.0 => /lib/x86_64-linux-gnu/libgpg-error.so.0 (0x00007f13e2503000)
    libicudata.so.66 => /usr/lib/x86_64-linux-gnu/libicudata.so.66 (0x00007f13e0a42000)
    libstdc++.so.6 => /usr/lib/x86_64-linux-gnu/libstdc++.so.6 (0x00007f13e0861000)
    libgcc_s.so.1 => /lib/x86_64-linux-gnu/libgcc_s.so.1 (0x00007f13e0846000)
ian@thebeb:/etc/php/7.4/fpm$ 

Answer 1

pcre2_set_depth_limit_8 is a library symbol reference (on my system it is in /usr/lib/apache2/modules/libphp8.0.so ) that appears, again on my system, to reside in /usr/lib/x86_64-linux-gnu/libpcre2-8.so.0.10.0 .

So, I suspect that the PCRE package on your system is damaged. Check the status of your libpcre2-8-0 package.

Or just do

ldd /usr/sbin/php-fpm7.4 | grep pcre2

and check where it points, or if it says that the library was not found (in the latter case you just need to apt-get install it, and apparently the dependency check system for that library is broken, since it didn't spot the lack).

If it does point to a.so file, then let's check said file: for example (I have only a Raspberry available)

 nm -gD  /usr/lib/arm-linux-gnueabihf/libpcre2-8.so.0.7.1

should report all the symbols in the library, and grep'ping for ours does find it:

 0000f508 T pcre2_set_depth_limit_8

If it did not , then that would mean that the library does not contain the symbol -- which to me indicates that the library has to be somehow damaged, since on other systems that symbol is there.

Ubuntu 20.04

I remembered I had a 20.04 available somewhere else. The library there is libpcre2-8.so.0.9.0 :

-rw-r--r-- 1 root root 584392 Dec  7  2019 /usr/lib/x86_64-linux-gnu/libpcre2-8.so.0.9.0

and the symbol is there. The Ubuntu package I have is libpcre2-8-0:amd64 .

 # nm -gD /usr/lib/x86_64-linux-gnu/libpcre2-8.so.0.9.0 | grep pcre2_set_depth_limit_8
 00000000000116f0 T pcre2_set_depth_limit_8