解决方案

对 oracle 所有者进程执行 su 的 dbora 脚本存在问题，而 systemd 无法跟踪该进程。
这是示例 dbora 脚本

ORA_HOME=/u01/app/oracle/product/12.1.0.2/dbhome_1
ORA_OWNER=oracle
case "" in
'start')
# Start the Oracle databases:
# The following command assumes that the oracle login
# will not prompt the user for any values
# Remove "&" if you don't want startup as a background process.
su - $ORA_OWNER -c "$ORA_HOME/bin/dbstart $ORA_HOME"
touch /var/lock/subsys/dbora
;;
'stop')
# Stop the Oracle databases:
# The following command assumes that the oracle login
# will not prompt the user for any values
su - $ORA_OWNER -c "$ORA_HOME/bin/dbshut $ORA_HOME"
rm -f /var/lock/subsys/dbora
;;
esac

通过这种安排，systemd 失去了对服务的控制，并且没有及时停止它。
更好的选择是直接在带有用户和所有者详细信息的指令下使用 dbstart 和 dbstop 脚本：

[Unit]
Description=The Oracle Database Service
After=network.target
[Service]
Type=forking
RemainAfterExit=yes
KillMode=none
TimeoutStopSec=5min
User=oracle                                      << Replace Oracle software owner details here 
Group=oinstall
ExecStart=$ORACLE_HOME/bin/dbstart $ORACLE_HOME &             ===> Please use absolute path here instead of the $ORACLE_HOME variable
ExecStop=$ORACLE_HOME/bin/dbshut $ORACLE_HOME                 ===> Please use absolute path here instead of the $ORACLE_HOME variable
Restart=no
[Install]
# Puts wants directive for the other units in the relationship
WantedBy=default.target

然后 systemd 可以控制服务

# systemctl status dbora.service
● dbora.service - The Oracle Database Service
Loaded: loaded (/usr/lib/systemd/system/dbora.service; enabled; vendor preset: disabled)
Active: active (running) since Wed 2017-02-01 12:19:53 GMT; 22s ago
Process: 3905 ExecStop=/u01/app/oracle/product/12.1.0.2/dbhome_1/bin/dbshut /u01/app/oracle/product/12.1.0.2/dbhome_1 (code=exited, status=0/SUCCESS)
Process: 4043 ExecStart=/u01/app/oracle/product/12.1.0.2/dbhome_1/bin/dbstart /u01/app/oracle/product/12.1.0.2/dbhome_1 & (code=exited, status=0/SUCCESS)
CGroup: /system.slice/dbora.service
├─4051 /u01/app/oracle/product/12.1.0.2/dbhome_1/bin/tnslsnr LISTENER -inherit
├─4143 ora_pmon_XXXXX

└─4477 ora_q003_XXXX

问题

在使用 Oracle 数据库 12.1.0.2 版本的 CentOS/RHEL 7 上，在服务器关闭期间尝试停止数据库时，自动关闭脚本出现以下错误：

# cat /u01/app/oracle/product/12.1.0.2/dbhome_1/shutdown.log
Processing Database instance "XXXX1": log file /u01/app/oracle/product/12.1.0.2/dbhome_1/shutdown.log
Info: Database instance "XXXX" already down (PMON process not there).

这表明在调用脚本之前 PMON 被强行关闭。
这是使用的配置

# cat dbora.service
[Unit]
Description=The Oracle Database Service
After=network.target
[Service]
Type=forking
# Type=oneshot
RemainAfterExit=yes
KillMode=none
# Set this to something larger if it has an impact
TimeoutStopSec=0
ExecStart=/u01/app/oracle/product/12.1.0.2/dbhome_1/bin/dbora start
ExecStop=/u01/app/oracle/product/12.1.0.2/dbhome_1/bin/dbora stop
[Install]
# Puts wants directive for the other units in the relationship
WantedBy=default.target

systemctl enable dbora.service
systemctl daemon-reload
systemctl start dbora.service