我正试图安装一些软件包，但每次都会遇到这个错误，我该如何修复它？不知道是否要安装此软件包或其他软件包

apt-get install mysql-server php5.6-mysql
Reading package lists... Done
Building dependency tree
Reading state information... Done
mysql-server is already the newest version (5.5.9999+default).
The following NEW packages will be installed:
php5.6-common php5.6-mysql
0 upgraded, 2 newly installed, 0 to remove and 398 not upgraded.
4 not fully installed or removed.
Need to get 872 kB of archives.
After this operation, 4924 kB of additional disk space will be used.
Get:1 https://packages.sury.org/php jessie/main amd64 php5.6-common amd64 5.6.36-1+0~20180505045733.13+jessie~1.gbp9b5cab [730 kB]
Get:2 https://packages.sury.org/php jessie/main amd64 php5.6-mysql amd64 5.6.36-1+0~20180505045733.13+jessie~1.gbp9b5cab [142 kB]
Fetched 872 kB in 0s (1047 kB/s)
Setting up systemd (232-25+deb9u3) ...
addgroup: The group `systemd-journal' already exists as a system group. Exiting.
adduser: The user `systemd-timesync' already exists. Exiting.
dpkg: error processing package systemd (--configure):
 subprocess installed post-installation script returned error exit status 1
Errors were encountered while processing:
 systemd
E: Sub-process /usr/bin/dpkg returned an error code (1)