● opendkim.service - DomainKeys Identified Mail (DKIM) Milter
   Loaded: loaded (/usr/lib/systemd/system/opendkim.service; enabled; vendor preset: disabled)
   Active: failed (Result: timeout) since Fri 2020-02-28 07:48:49 UTC; 17min ago
     Docs: man:opendkim(8)
           man:opendkim.conf(5)
           man:opendkim-genkey(8)
           man:opendkim-genzone(8)
           man:opendkim-testadsp(8)
           man:opendkim-testkey
           http://www.opendkim.org/docs.html
  Process: 763 ExecStart=/usr/sbin/opendkim $OPTIONS (code=exited, status=0/SUCCESS)

Feb 28 07:47:19 instance systemd[1]: Starting DomainKeys Identified Mail (DKIM) Milter...
Feb 28 07:47:19 instance systemd[1]: New main PID 764 does not belong to service, and PID file is not owned by root. Refusing.
Feb 28 07:47:19 instance systemd[1]: New main PID 764 does not belong to service, and PID file is not owned by root. Refusing.
Feb 28 07:47:19 instance opendkim[765]: OpenDKIM Filter v2.11.0 starting (args: -x /etc/opendkim.conf -P /var/run/opendkim/opendkim.pid)
Feb 28 07:48:49 instance systemd[1]: opendkim.service start operation timed out. Terminating.
Feb 28 07:48:49 instance opendkim[765]: OpenDKIM Filter: mi_stop=1
Feb 28 07:48:49 instance opendkim[765]: OpenDKIM Filter v2.11.0 terminating with status 0, errno = 0
Feb 28 07:48:49 instance systemd[1]: Failed to start DomainKeys Identified Mail (DKIM) Milter.
Feb 28 07:48:49 instance systemd[1]: Unit opendkim.service entered failed state.
Feb 28 07:48:49 instance systemd[1]: opendkim.service failed.

[root@instance multi-user.target.wants]# systemd-cgls -a
Failed to list cgroup tree /docker/76a810c3174c5b85446942a61732c3c601ed9f6b576548beaeab63a2d7226604/docker/76a810c3174c5b85446942a61732c3c601ed9f6b576548beaeab63a2d7226604: No such file or directory

[root@instance multi-user.target.wants]# cat /etc/os-release
NAME="CentOS Linux"
VERSION="7 (Core)"
ID="centos"
ID_LIKE="rhel fedora"
VERSION_ID="7"
PRETTY_NAME="CentOS Linux 7 (Core)"
ANSI_COLOR="0;31"
CPE_NAME="cpe:/o:centos:centos:7"
HOME_URL="https://www.centos.org/"
BUG_REPORT_URL="https://bugs.centos.org/"

CENTOS_MANTISBT_PROJECT="CentOS-7"
CENTOS_MANTISBT_PROJECT_VERSION="7"
REDHAT_SUPPORT_PRODUCT="centos"
REDHAT_SUPPORT_PRODUCT_VERSION="7"


docker --version                                                                                                                                     11:25:34
systemd 237
+PAM +AUDIT +SELINUX +IMA +APPARMOR +SMACK +SYSVINIT +UTMP +LIBCRYPTSETUP +GCRYPT +GNUTLS +ACL +XZ +LZ4 +SECCOMP +BLKID +ELFUTILS +KMOD -IDN2 +IDN -PCRE2 default-hierarchy=hybrid