官方文件
https://docs.influxdata.com/influxdb/v2.1/reference/cli/influxd/
https://www.freedesktop.org/software/systemd/man/systemd.service.html

總結：
1、只要把文字型別的可執行檔案放入/usr/lib/systemd/system/就能實現systemctl的操作，執行systemctl enable XX就是把XX加入開機啟動，即透過/usr/lib/systemd/system/XX建立軟連線/etc/systemd/system/multi-user.target.wants/XX
2、systemctl就是集service和chkconfig一體的功能，systemcel enable就是類似chkconfig
[root@TDBDEV2 Prometheus]# systemctl enable influxdb
Created symlink from /etc/systemd/system/multi-user.target.wants/influxdb.service to /usr/lib/systemd/system/influxdb.service.
3、/usr/lib/systemd/system/influxd不能是二進位制的可執行檔案，只能是一個sh這樣的文字的可執行檔案
4、直接把二進位制檔案influxd加入/etc/init.d/無法正常service influxd start啟動，加入/usr/lib/systemd/system/也無法正常systemctl start influxd啟動
5、influxdb.service服務裡面不能直接寫成ExecStart=/usr/bin/influxd &，systemctl start influxdb會報錯Error: unknown command "&" for "influxd";也不能寫成ExecStart=/usr/bin/influxd，systemctl start influxdb會不停的自動重啟，因為服務啟動時間過長，達到超時時間就自動結束了服務並不停的自動重啟然後出現報錯influxdb.service start operation timed out. Terminating。因為influxd沒有/usr/bin/influxd --help |grep daemonize或/usr/bin/influxd --help |grep quite這種後臺執行的引數，所以還是需要&讓它在後臺跑，但是&又無直接ExecStart=/usr/bin/influxd &，所以需要藉助“/bin/bash -c”將一個長字串當作一條完整的命令來執行，即寫成ExecStart=/bin/bash -c "/usr/bin/influxd &"

啟動服務：systemctl start xxx.service
關閉服務：systemctl stop xxx.service
重啟服務：systemctl restart xxx.service
顯示服務的狀態：systemctl status xxx.service
在開機時啟用服務：systemctl enable xxx.service
在開機時禁用服務：systemctl disable xxx.service
檢視服務是否開機啟動：systemctl is-enabled xxx.service
檢視已啟動的服務列表：systemctl list-unit-files|grep enabled
檢視啟動失敗的服務列表：systemctl --failed
重新載入一個服務的配置檔案：systemctl reload xxx.service
過載所有修改過的配置檔案：systemctl daemon-reload
檢視systemctl服務相關日誌：journalctl -xe

把下載的二進位制檔案influxd加入systemctl的操作
實驗1：
直接把下載的二進位制檔案influxd加入/etc/init.d/無法正常service influxd start啟動，加入/usr/lib/systemd/system/也無法正常systemctl start influxd啟動，實驗失敗
[root@TDBDEV2 Prometheus]# wget https://dl.influxdata.com/influxdb/releases/influxdb2-2.1.1-linux-amd64.tar.gz
[root@TDBDEV2 Prometheus]# tar -zxcf influxdb2-2.1.1-linux-amd64.tar.gz
[root@TDBDEV2 ~]# cp /Prometheus/influxdb2-2.1.1-linux-amd64/influxd /etc/init.d/
[root@TDBDEV2 ~]# cd /etc/init.d/

[root@TDBDEV2 init.d]# service influxd start
Error: unknown command "start" for "influxd"

[root@TDBDEV2 init.d]# chkconfig influxd on
service influxd does not support chkconfig

[root@TDBDEV2 init.d]# cp /Prometheus/influxdb2-2.1.1-linux-amd64/influxd /usr/lib/systemd/system/
[root@TDBDEV2 init.d]# systemctl start influxd
Failed to start influxd.service: Unit not found.

實驗2：
參考/usr/lib/systemd/system/mysqld.service來配置influxd成systemctl啟動，實驗成功

[root@TDBDEV2 Prometheus]# cp /Prometheus/influxdb2-2.1.1-linux-amd64/influxd /usr/bin/

[root@TDBDEV2 Prometheus]# useradd influxd

[root@TDBDEV2 Prometheus]# vim /usr/lib/systemd/system/influxdb.service
--新增如下如下資訊
[Unit]
Description=Influxdb
After=network.target

[Install]
WantedBy=multi-user.target

[Service]
User=influxdb
Group=influxdb
Type=forking
ExecStart=/bin/bash -c "/usr/bin/influxd &"
Restart=on-failure

[root@TDBDEV2 Prometheus]# systemctl enable influxdb
Created symlink from /etc/systemd/system/multi-user.target.wants/influxdb.service to /usr/lib/systemd/system/influxdb.service.

[root@TDBDEV2 Prometheus]# systemctl start influxdb
[root@TDBDEV2 Prometheus]#

透過yum install自動新增到systemctl的方式反推如何把可執行檔案新增到systemctl的操作
[root@TDBDEV2 ~]# yum install influxdb2
出現如下資訊，說明啟動指令碼來自/usr/lib/systemd/system/influxd
```bash
Resolving Dependencies
--> Running transaction check
---> Package influxdb2.x86_64 0:2.1.1-1 will be installed
--> Finished Dependency Resolution
Dependencies Resolved
====================================================================================================================
 Package                     Arch                     Version                      Repository                  Size
====================================================================================================================
Installing:
 influxdb2                   x86_64                   2.1.1-1                      influxdb                   103 M
Transaction Summary
====================================================================================================================
Install  1 Package
Total download size: 103 M
Installed size: 103 M
Is this ok [y/d/N]: y
Downloading packages:
...
  Installing : influxdb2-2.1.1-1.x86_64                                                                         
1/1 Created symlink from /etc/systemd/system/influxd.service to /usr/lib/systemd/system/influxdb.service.
Created symlink from /etc/systemd/system/multi-user.target.wants/influxdb.service to /usr/lib/systemd/system/influxd                                                                         b.service.
  Verifying  : influxdb2-2.1.1-1.x86_64                                                                         
1/1
Installed:
  influxdb2.x86_64 0:2.1.1-1
Complete!
```

/usr/lib/systemd/system/influxdb.service指令碼內容
[root@TDBDEV2 ~]# cat /usr/lib/systemd/system/influxdb.service
```bash
# If you modify this, please also make sure to edit init.sh
[Unit]
Description=InfluxDB is an open-source, distributed, time series database
Documentation=https://docs.influxdata.com/influxdb/
After=network-online.target

[Service]
User=influxdb
Group=influxdb
LimitNOFILE=65536
EnvironmentFile=-/etc/default/influxdb2
ExecStart=/usr/lib/influxdb/scripts/influxd-systemd-start.sh
KillMode=control-group
Restart=on-failure
Type=forking
PIDFile=/var/lib/influxdb/influxd.pid

[Install]
WantedBy=multi-user.target
Alias=influxd.service
```

/usr/lib/influxdb/scripts/influxd-systemd-start.sh指令碼內容
[root@TDBDEV2 ~]# cat /usr/lib/influxdb/scripts/influxd-systemd-start.sh
```bash
#!/bin/bash -e

/usr/bin/influxd &
PID=$!
echo $PID > /var/lib/influxdb/influxd.pid

PROTOCOL="http"
BIND_ADDRESS=$(influxd print-config --key-name http-bind-address)
TLS_CERT=$(influxd print-config --key-name tls-cert | tr -d '"')
TLS_KEY=$(influxd print-config --key-name tls-key | tr -d '"')
if [ -n "${TLS_CERT}" ] && [ -n "${TLS_KEY}" ]; then
  echo "TLS cert and key found -- using https"
  PROTOCOL="https"
fi
HOST=${BIND_ADDRESS%%:*}
HOST=${HOST:-"localhost"}
PORT=${BIND_ADDRESS##*:}

set +e
attempts=0
url="$PROTOCOL://$HOST:$PORT/ready"
result=$(curl -k -s -o /dev/null $url -w %{http_code})
while [ "${result:0:2}" != "20" ] && [ "${result:0:2}" != "40" ]; do
  attempts=$(($attempts+1))
  echo "InfluxDB API at $url unavailable after $attempts attempts..."
  sleep 1
  result=$(curl -k -s -o /dev/null $url -w %{http_code})
done
echo "InfluxDB started"
set -e
```

/usr/bin/influxd檔案大小
[root@TDBDEV2 ~]# ll /usr/bin/influxd
-rwxrwxr-x. 1 root root 178700904 Nov  8 19:10 /usr/bin/influxd

/Prometheus/influxdb2-2.1.1-linux-amd64/influxd下載的二進位制檔案大小
[root@TDBDEV2 ~]# ll /Prometheus/influxdb2-2.1.1-linux-amd64/influxd
-rwxrwxr-x. 1 1001 1002 178700904 Nov  8 19:10 /Prometheus/influxdb2-2.1.1-linux-amd64/influxd

備註：實驗證明下載的二進位制檔案wget https://dl.influxdata.com/influxdb/releases/influxdb2-2.1.1-linux-amd64.tar.gz解壓出來的/Prometheus/influxdb2-2.1.1-linux-amd64/influxd和yum install influxdb2安裝的/usr/bin/influxd是一樣的

systemctl介紹，以influxdb為例把可執行檔案新增到systemctl的實驗

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