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 raspberry pi 零 w，设置一个脚本来监控 bme280 传感器，并将值写入文件。当脚本从命令行启动时，这非常有效，当脚本通过 systemd 启动时，文件不会被写入。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但没有成功，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 senselog.csv 文件，那么在启动时 systemd 服务会创建新的文件但没有任何数据，我们将不胜感激。

Answer 1

StandardOutput 的 file 属性仅适用于 systemd 版本 236。您使用的是什么版本？

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

如果版本低于 236 并且您t/don不想升级，您可以简单地将 ExecStart 行更新为：

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

...然后将 StandardOutput 行恢复为默认值。

Answer 2

所以解决方案是在 python 脚本中对我们正在写入的文件实际调用 .close() ，然后 systemd 服务会按预期工作。大声喊到这个线程：https://askubuntu.com/questions/83549/python-script-wont-write-data-when-ran-from-cron 最后一个答案 = 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) ```

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

Systemd service does not write python script to file, python script runs nominally when executed from cli

python

raspberry-pi

systemd