Score:1

Ubuntu

Cron job seems to be running but no output and got killed after a while

VII

2/10/23, 12:33 PM

I am trying to run my python scripts with crontab. I have 2 python scripts in the same directory. The first one file1.py has just 1 line print(1). The second file file2.py begins with print(2) but then a long code to query and update data in my SQL database.

My setup in crontab -e is something like this (I set up the files to run every minute and save the output to cron.log

* * * * * cd /path/to/files && python3 file1.py >> /path/to/files/cron.log 2>&1
* * * * * cd /path/to/files && python3 file2.py >> /path/to/files/cron.log 2>&1

When I check the output in cron.log, at first I only see 1, which is from file1.py but I don't see any 2, the output of file2.py. However, after a while, maybe 10 minutes or so, I see Killed in cron.log.

I think the Killed message means cron started the job to run file2.py and killed the job after a while. I am not interested in the reason why cron kills my job. What I am confused is if cron started the job to run file2.py, why there is no 2 in cron.log. All I see is 1 and Killed. Both of these files run without any problem when I run them manually. Appreciate any help

124

0 + 0

python

cron

VII

2/10/23, 1:03 PM

sorry my bad, edited

Score:1

Ubuntu

steeldriver

2/10/23, 1:44 PM

I suspect it's because when the output is redirected, python3 buffers its standard output stream - and the buffer is not getting flushed when the process is killed.

To illustrate, given

$ cat file2.py
import time
print(2)
time.sleep(5)

then

$ timeout 3 python3 file2.py
2

whereas

$ timeout 3 python3 file2.py | cat
Terminated

If you force python3 to unbuffer its streams you will likely see the expected log output:

$ timeout 3 python3 -u file2.py | cat
2
Terminated

0 + 0

VII

2/10/23, 2:15 PM

thanks for your answer, yes I need to unbuffer the output. Sorry this is my first time asking on this community so can't upvote your answer yet (not enough reputation).

mondotofu

2/11/23, 12:16 AM

Would it make sense to write the output to two separate cron.log files to alleviate contention?

steeldriver

2/11/23, 12:49 AM

@mondotofu that's a good question - I really don't know

Elon Musk

I sit in a Tesla and translated this thread with Ai:

EN: Cron job seems to be running but no output and got killed after a while

TH: ดูเหมือนว่างาน Cron จะทำงาน แต่ไม่มีเอาต์พุตและถูกฆ่าหลังจากผ่านไประยะหนึ่ง

RO: Lucrarea Cron pare să funcționeze, dar nicio ieșire și a fost ucis după un timp

RU: Работа Cron, кажется, работает, но ничего не выводится и через некоторое время была убита.

VI: Công việc định kỳ dường như đang chạy nhưng không có đầu ra và bị tắt sau một thời gian

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