Centos – MongoDB: why the mongod service is shutdown

When I use daemon service to start mongodb, MongoDB is always received kill signal by system(CentOS7.3) after about 2 minutes:

Log: [signalProcessingThread] got signal 15 (Terminated)

But when I run it Manually in shell: /data/mongo/bin/3.4/mongod -f /data/mongo/config/uxdb_27019.conf –fork , it runs ok.

My mongodb daemon service: /usr/lib/systemd/system/mongod.service

[Unit]
Description=mongodb
After=network.target·
After=syslog.target

[Service]|
Type=forking
User=mongo
ExecStart=/data/mongo/bin/3.4/mongod -f /data/mongo/config/uxdb_27019.conf
PrivateTmp=true
PIDFile=/data/mongo/pid/mongod_27019.pid
LimitFSIZE=infinity
LimitCPU=infinity
LimitAS=infinity
LimitNOFILE=32000
LimitNPROC=32000

[Install]
WantedBy=multi-user.target

Which process is terminate mongod service ?

2017-08-08T14:57:55.638+0800 I NETWORK  [conn12] received client metadata from 10.10.9.51:56714 conn12: { driver: { name: "mongo-java-driver", version: "3T_5.0.0-74-g1de6631-dirty" }, os: { type: "Windows", name: "Windows Server 2012 R2", architecture: "amd64", version: "6.3" }, platform: "Java/Oracle Corporation/1.8.0_121-b13" }
2017-08-08T14:59:14.169+0800 I CONTROL  [signalProcessingThread] got signal 15 (Terminated), will terminate after current cmd ends
2017-08-08T14:59:14.169+0800 I NETWORK  [signalProcessingThread] shutdown: going to close listening sockets...