For debugging u can redirect the output into a file, eg:
* * * * * root /usr/bin/python /home/debian/Desktop/SimB.py >>
/home/debian/err.txt 2>&1
(write this all in one line)

However, if your program is an X program the error will be something like:
"cannot open display"

But: All Window Managers i know provide methods to autostart a x-program....
If your WM is lxde the u will find a good explanation here:
https://wiki.archlinux.org/index.php/LXDE#Autostart



On Sun, Apr 17, 2016 at 3:20 AM, evilwulfie <[email protected]> wrote:

> I Am saying that if your depending on the GUI for any part of your program
> it may expect the xwindow system to be active before
> it starts, then seeing that the GUI is not running just exits.
>
> It's hard to second guess what your program is doing here but it "may" be
> the issue.
>
> try checking for the xwindow system being running before starting your
> program.
>
>
>
>
>
>
> On 4/16/2016 6:16 PM, John Baker wrote:
>
> Hi Wulf Man,
> My GUI is part of a simulation program. There's a lot of calculation and
> the GUI to allow me to enter some parameters and display the results on a
> graph. You're saying that I have to start up my calculation part of the
> program and then the GUI?
> John
>
> On Saturday, April 16, 2016 at 5:37:07 PM UTC-7, Wulf Man wrote:
>>
>> If this is a GUI only program you need to start your program
>> after the GUI is up, I don't see this check in your crontab file
>> Been too long since i have done this but i am sure google is your friend
>>
>>
>>
>> On 4/16/2016 4:53 PM, John Baker wrote:
>>
>> Hi Dieter,
>> Still not working. I have a hunch that the problem is with Tkinter but
>> can't tell. I have to run my GUI program SimB.py with the terminal program
>> on the BBB, typing sudo python SimB.py, then it runs happily.
>>
>> *Here's my crontab in /etc:*
>> # /etc/crontab: system-wide crontab
>> # Unlike any other crontab you don't have to run the `crontab'
>> # command to install the new version when you edit this file
>> # and files in /etc/cron.d. These files also have username fields,
>> # that none of the other crontabs do.
>>
>> SHELL=/bin/sh
>> PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin
>>
>> # m h dom mon dow user command
>> 17 * * * * root    cd / && run-parts --report /etc/cron.hourly
>> 25 6 * * * root test -x /usr/sbin/anacron || ( cd / && run-parts
>> --report /etc/cron.daily )
>> 47 6 * * 7 root test -x /usr/sbin/anacron || ( cd / && run-parts
>> --report /etc/cron.weekly )
>> 52 6 1 * * root test -x /usr/sbin/anacron || ( cd / && run-parts
>> --report /etc/cron.monthly )
>> #
>> @reboot root /usr/bin/python /home/debian/Desktop/SimB.py
>> * * * * * root /usr/bin/python /home/debian/Desktop/SimB.py
>>
>> *and here's from the syslog file that doesn't tell me anything:*
>>
>> Apr 16 23:37:01 beaglebone /USR/SBIN/CRON[2293]: (root) CMD (sudo python
>> /home/debian/Desktop/SimB.py)
>>
>> Apr 16 23:37:01 beaglebone /USR/SBIN/CRON[2294]: (debian) CMD (sudo
>> python /home/debian/Desktop/SimB.py)
>>
>> Apr 16 23:37:01 beaglebone /USR/SBIN/CRON[2295]: (root) CMD
>> (/usr/bin/python /home/debian/Desktop/SimB.py)
>>
>> Apr 16 23:37:14 beaglebone /USR/SBIN/CRON[2292]: (CRON) info (No MTA
>> installed, discarding output)
>>
>> Apr 16 23:37:14 beaglebone /USR/SBIN/CRON[2290]: (CRON) info (No MTA
>> installed, discarding output)
>>
>> Apr 16 23:37:14 beaglebone /USR/SBIN/CRON[2291]: (CRON) info (No MTA
>> installed, discarding output)
>>
>>
>> I can successfully run my program with a keyboard attached to my BBB
>> using sudo python SimB.py, have to use the sudo, otherwise gets a Tkinter
>> error. I just now double-checked and my GUI program SimB.py runs very
>> happily. Cannot run SimB.py thru putty as it gives the Tkinter error.
>>
>> Any ideas?
>> Thanks,
>> John
>>
>> On Saturday, April 16, 2016 at 1:04:21 AM UTC-7, Dieter Wirz wrote:
>>>
>>> On Sat, Apr 16, 2016 at 5:57 AM, John Baker <[email protected]>
>>> wrote:
>>>
>>>> John Minton,
>>>> I gave crontab a try and of course it didn't work. It seems like this
>>>> should be a piece of cake to do. I probably did something wrong. I checked
>>>> the syslog and see an error: "No MTA installed."
>>>>
>>>
>>> ​
>>> If u​
>>>
>>> ​ have an error in ​crontab the crontab tries to send you an Email...
>>> And of coarse cannot without MTA;)
>>>
>>> My crontab file says:
>>>> ​ ​
>>>> @reboot sudo python /home/debian/Desktop/myProg.py
>>>> * * * * * sudo python /home/debian/Desktop/myProg.py
>>>>
>>>
>>> ​ The are two crontabs, users and system crontab.
>>> Users crontab you can change with
>>> $ crontab -e
>>> System crontab with
>>> $ sudo nano /etc/crontab
>>>
>>> If u want to run a process as root, then best is, if u add
>>>
>>>> @reboot root /usr/bin/python /home/debian/Desktop/myProg.py
>>>> * * * * * root /usr/bin/python /home/debian/Desktop/myProg.py
>>>>
>>> to /etc/crontab
>>>
>>> HTH
>>>
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