Systemd服务不会将python脚本写入文件，python脚本在从cli执行时名义上运行

Question

使用覆盆子pi零w，设置一个脚本，用于监视bme280传感器，并将值写入文件。当从命令行启动脚本时，这非常有效，当脚本通过systemd启动时，不会写入文件。请在下面找到脚本和systemd服务。

已将标准输出设置为绝对路径而没有运气，python脚本写入指令也设置为绝对路径。

系统服务：

[Unit]
Description=bme280 sensor log startup
After=network.target

[Service]
ExecStart=/usr/bin/python3 -u /home/pi/bme.py
WorkingDirectory=/home/pi
StandardOutput=file:/home/pi/senselog.csv
StandardError=inherit
Restart=always
User=pi

[Install]
WantedBy=multi-user.target

python脚本：

import time
from time import strftime
import board
import busio
import adafruit_bme280

# Create library object using our Bus I2C port
i2c = busio.I2C(board.SCL, board.SDA)
bme280 = adafruit_bme280.Adafruit_BME280_I2C(i2c,address=0x76)

# OR create library object using our Bus SPI port
#spi = busio.SPI(board.SCK, board.MOSI, board.MISO)
#bme_cs = digitalio.DigitalInOut(board.D10)
#bme280 = adafruit_bme280.Adafruit_BME280_SPI(spi, bme_cs)

# change this to match the location's pressure (hPa) at sea level
bme280.sea_level_pressure = 1013.25

with open("/home/pi/senselog.csv", "a") as log:
    while True:

        temp_h = bme280.temperature
        humidity = bme280.humidity
        pressure = bme280.pressure
        log.write("{0},{1}\n".format(strftime("%Y-%m-%d %H:%M:%S"),str([temp_h,humidity,pressure])))
        time.sleep(60)

如果我删除了senselog.csv文件，那么在启动时，systemd服务会创建文件，但没有数据，任何帮助都表示赞赏。

Answer 1

file属性StandardOutput只有systemd版本236可用。你有什么版本？

pi@wifi-relay:~ $ systemd --version

systemd 232
+PAM +AUDIT +SELINUX +IMA +APPARMOR +SMACK +SYSVINIT +UTMP +LIBCRYPTSETUP +GCRYPT +GNUTLS +ACL +XZ +LZ4 +SECCOMP +BLKID +ELFUTILS +KMOD +IDN

如果它低于236版并且你不能/不想升级，你可以简单地将你的ExecStart行更新为：

/usr/bin/python3 -u /home/pi/bme.py >1 /home/pi/senselog.csv

...然后将StandardOutput线恢复到默认值。

Answer 2

因此解决方案是在python脚本中实际调用我们正在写入的文件上的.close（），然后systemd服务按预期工作。喊出这个帖子：https://askubuntu.com/questions/83549/python-script-wont-write-data-when-ran-from-cron最后一个回答= f.close（）

和工作脚本文件：

from time import strftime
import board
import busio
import adafruit_bme280

# Create library object using our Bus I2C port
i2c = busio.I2C(board.SCL, board.SDA)
bme280 = adafruit_bme280.Adafruit_BME280_I2C(i2c,address=0x76)

# OR create library object using our Bus SPI port
#spi = busio.SPI(board.SCK, board.MOSI, board.MISO)
#bme_cs = digitalio.DigitalInOut(board.D10)
#bme280 = adafruit_bme280.Adafruit_BME280_SPI(spi, bme_cs)

# change this to match the location's pressure (hPa) at sea level
bme280.sea_level_pressure = 1013.25

with open("/home/pi/senselog.csv", "w") as log:
    while True:

        temp_h = bme280.temperature
        humidity = bme280.humidity
        pressure = bme280.pressure
        log.write("{0},{1}\n".format(strftime("%Y-%m-%d %H:%M:%S"),str([temp_h,humidity,pressure])))
        log.close()
        time.sleep(60) ```