我无法在我的Raspberry Pi(python，btmgmt)附近列出BLE设备 [英] I cannot list up the BLE devices in the neighbourhood of my Raspberry Pi (python, btmgmt)

问题描述

我想使用从cron脚本调用的python脚本在Raspberry环境中扫描ble设备.但是，当我在cron中执行此操作时(我是说我将其添加到sudo crontab -e中)，我总是以空列表结尾.

I want to scan the ble devices in the environment of my Raspberry, by using a python script called from a cron script. But when I do this in cron (I mean I added to sudo crontab -e), I allways end up with an empty list.

当我以pi用户身份登录时-btmgmt可以(仅)在具有su权限的情况下可以正常工作:

when I am logged in as pi user - btmgmt works (only) fine with su permissions:

pi@Pluto:~ $ btmgmt find
Unable to start discovery. status 0x14 (Permission Denied)

pi@Pluto:~ $ sudo btmgmt find
Discovery started
hci0 type 7 discovering on
hci0 dev_found: 77:F8:D7:8A:1E:E5 type LE Random rssi -83 flags 0x0000 
...

所以在我的python脚本中，我写道:

so in my python script I wrote:

flog.write("P01:\r\n")
out = subprocess.Popen(['sudo', '/usr/bin/btmgmt', 'find'], stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
stdout, stderr = out.communicate()
flog.write("stderr: " + str(stderr) + "\r\n")
cDvc = stdout.split('\n')
flog.write("Amount of lines = " + str(len(cDvc)) + "\r\n")
for line in cDvc:
    line = line + '\r\n'
    if debugflag:
        print(line)
        flog.write(line)
..

从shell提示符运行此脚本可以正常工作..在我得到的日志文件(flog)中:...

Running this script from the shell prompt works fine.. in the log-file (flog) I get: ...

P01:
stderr: None
Amount of lines = 40
Discovery started
hci0 type 7 discovering on
hci0 dev_found: 70:D0:FD:74:34:AC type LE Random rssi -59 flags 0x0000 
AD flags 0x1a 
..

运行与crontab -e行相同的脚本:没有设备显示&我找不到原因:

Running this same script as a crontab -e line: no devices show up & I cannot find cause:

...
P01:
stderr: None
Amount of lines = 1
P02:
...

有人可以帮我吗?

推荐答案

我遇到了完全相同的问题.我需要使用树莓派来检查附近是否还存在某些特定的蓝牙设备，并向监测服务发送心跳信号.

I have exact the same issue. I need to use a raspberry pi to check if some specific bluetooth devices are alive nearby and to send a heartbeat to monitoring service.

在像 * * * * * sudo btmgmt find>这样的cron作业中执行命令时，我没有从 sudo btmgmt find 中获得任何输出./tmp/ble_devices.txt ，如果我使用python捕获Popen调用的输出，都不会.因此我问自己是否可以在另一个屏幕上执行它，并且它可以工作.

I was not getting any output from sudo btmgmt find when the command was executed in a cron job like * * * * * sudo btmgmt find > /tmp/ble_devices.txt, neither if I was using python to capture the output from Popen call. So I asked myself if I could executed it into another screen, and it worked.

我的解决方案很糟糕.我做了以下事情:

My solution is quite hackish. I did the following:

1. 在树莓派上安装了屏幕工具: sudo apt install screen
2. 创建了一个用于运行扫描命令的屏幕: screen -S blescan
3. 从屏幕 ctrl + a + d
离开自己
4. 在/home/pi/scan_job 中创建内容如下的shell脚本:

1. Installed the screen tool on raspberry pi: sudo apt install screen
2. Created a screen for running the scan command: screen -S blescan
3. Detached myself from screen ctrl+a+d
4. Created a shell script in /home/pi/scan_job with the content:

   #!/bin/bash 
   cd <to python project> && ./<file to be executed>

1. 使其成为可执行文件 chmod + x/home/pi/scan_job
2. 设置cronjob以在 blescan 屏幕中执行文件:

1. Made it executable chmod +x /home/pi/scan_job
2. Set cronjob to execute the file in blescan screen:

*/10 * * * * screen -S blescan -X screen '/home/pi/scan_job'

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