Nohup 没有将日志写入输出文件

Question

I am using the following command to run a python script in the background:

nohup ./cmd.py > cmd.log &

But it appears that nohup is not writing anything to the log file. cmd.log is created but is always empty. In the python script, I am using sys.stdout.write instead of print to print to standard output. Am I doing anything wrong?

Answer 1

您可以使用-u标志运行 Python 以避免输出缓冲：

nohup python -u ./cmd.py > cmd.log &

Answer 2

It looks like you need to flush stdout periodically (eg sys.stdout.flush() ). In my testing Python doesn't automatically do this even with print until the program exits.

Answer 3

• Using -u with nohup worked for me. Using -u will force the stdout , stderr streams to be unbuffered. It will not affect stdin. Everything will be saved in " nohup.out " file. Like this-

   nohup python -u your_code.py &

  You can also save it into your directory. This way-

   nohup python -u your_code.py > your_directory/nohup.out &

• Also, you can use PYTHONUNBUFFERED . If you set it to a non-empty string it will work same as the -u option. For using this run below commands before running python code.

   export PYTHONUNBUFFERED=1

  or

  export PYTHONUNBUFFERED=TRUE

PS- I will suggest using tools like cron-job to run things in the background and scheduled execution.

Answer 4

export PYTHONUNBUFFERED=1
nohup ./cmd.py > cmd.log &

or

nohup python -u ./cmd.py > cmd.log &

https://docs.python.org/2/using/cmdline.html#cmdoption-u

Answer 5

Python 3.3 and above has a flush argument to print and this is the only method that worked for me.

print("number to train = " + str(num_train), flush=True)
print("Using {} evaluation batches".format(num_evals), flush=True)

Answer 6

I had a similar issue, but not connected with a Python process. I was running a script which did a nohup and the script ran periodically via cron.

I was able to resolve the problem by:

1. redirecting the stdin , stdout and stderr
2. ensuring the the script being invoked via nohup didn't run anything else in the background

PS: my scripts were written in ksh running on RHEL

Answer 7

I run my scripts in the following way and I have no problem at all:

nohup python my_script.py &> my_script.out &

comparing with your syntax looks like you are only missing a "&" symbol after your input...