root@test-1-blog1:~# uname -a
Linux test-1-blog1 4.4.0-159-generic #187-Ubuntu SMP Thu Aug 1 16:28:06 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux
root@test-1-blog1:~# mount | grep 'on / '
/var/lib/lxc/ubuntu-xenial-amd64/rootfs on / type overlayfs (rw,relatime,lowerdir=/var/lib/lxc/ubuntu-xenial-amd64/rootfs,upperdir=/var/lib/lxc/test-1-blog1/delta0,workdir=/var/lib/lxc/test-1-blog1/olwork)
root@test-1-blog1:~# ls /posix.ini
ls: cannot access '/posix.ini': No such file or directory
root@test-1-blog1:~# ucf -v /usr/share/php7.2-common/common/posix.ini /posix.ini
ucf: The new file is /usr/share/php7.2-common/common/posix.ini
ucf: The Destination file is /posix.ini
ucf: The Source directory is /usr/share/php7.2-common/common
ucf: The State directory is /var/lib/ucf
The hash file exists
egrep [[:space:]]\/posix\.ini$ /var/lib/ucf/hashfile
debconf: unable to initialize frontend: Dialog
debconf: (No usable dialog-like program is installed, so the dialog based frontend cannot be used. at /usr/share/perl5/Debconf/FrontEnd/Dialog.pm line 76.)
debconf: falling back to frontend: Readline
ucf: The new file is /usr/share/php7.2-common/common/posix.ini
ucf: The Destination file is /posix.ini
ucf: The Source directory is /usr/share/php7.2-common/common
ucf: The State directory is /var/lib/ucf
The hash file exists
egrep [[:space:]]\/posix\.ini$ /var/lib/ucf/hashfile

Creating config file /posix.ini with new version
(egrep -v "[[:space:]]\/posix\.ini$" "/var/lib/ucf/hashfile";
211c41c33bec001c072a7e1040ce1fb8  /etc/bird/bird.conf
84f5cc8381efdbafc88e4bfacc81b58a  /etc/bird/bird6.conf
0877786daf8479dd91be0f89f223a102  /etc/php/7.2/mods-available/calendar.ini
72def1d4663c5350713006af725f21ae  /etc/php/7.2/mods-available/ctype.ini
7b3bf6064e6bd1749e5f1a3dd56592b3  /etc/php/7.2/mods-available/exif.ini
3eb68bf4e22faed68c673430081b1a08  /etc/php/7.2/mods-available/fileinfo.ini
b245857286d2cff077355dd82086c950  /etc/php/7.2/mods-available/ftp.ini
7dfbed71c04bbd15100e719b20b7c764  /etc/php/7.2/mods-available/gettext.ini
f875ac0ca30dea610b2adc421b9e997e  /etc/php/7.2/mods-available/iconv.ini
2bcf2cd02149a7b3118f9a8ed7cfe1b3  /etc/php/7.2/mods-available/pdo.ini
9dafa1a822dd003107e1686818a191fd  /etc/php/7.2/mods-available/phar.ini
0f55f144c06b074b7c0a498928001452  /etc/php/7.2/mods-available/posix.ini
894f4d6c5c36f658499b941a02bbc9a7  /etc/php/7.2/mods-available/shmop.ini
5c9f4598aa9e02021783e540fc023c66  /etc/php/7.2/mods-available/sockets.ini
0ac70c35787ea579baefc56e36ea9c47  /etc/php/7.2/mods-available/sysvmsg.ini
a4c2616a57351dc93cb36e1f41c63926  /etc/php/7.2/mods-available/sysvsem.ini
46bf0b73759bfdd7fcf431ea42d03c2f  /etc/php/7.2/mods-available/sysvshm.ini
cb36a25e9c9d2c975cb49bbb56f16465  /etc/php/7.2/mods-available/tokenizer.ini
0f55f144c06b074b7c0a498928001452  /posix.ini
root@test-1-blog1:~# stat /posix.ini
  File: '/posix.ini'
  Size: 71              Blocks: 8          IO Block: 4096   regular file
Device: fd01h/64769d    Inode: 1526985     Links: 1
Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2019-08-15 16:41:54.000000000 +0000
Modify: 2019-08-07 10:47:18.000000000 +0000
Change: 2019-08-15 17:05:49.559895053 +0000
 Birth: -
root@test-1-blog1:~# getfacl /posix.ini
getfacl: Removing leading '/' from absolute path names
# file: posix.ini
# owner: root
# group: root
user::rw-
group::r--
other::r--

root@test-1-blog1:~# lsattr /posix.ini
-------------e-- /posix.ini
root@test-1-blog1:~# sudo -u www-data cat /posix.ini
cat: /posix.ini: Permission denied
root@test-1-blog1:~# chmod 0644 /posix.ini
root@test-1-blog1:~# sudo -u www-data cat /posix.ini
; configuration for php common module
; priority=20
extension=posix.so
root@test-1-blog1:~# (set -x; strace ucf /usr/share/php7.2-common/common/posix.ini /posix2.ini) 2>&1 >/dev/null | curl -F 'f:1=<-' ix.io
http://ix.io/1RNz