python process wrapper

Question

i have a java program which runs on a particular port in ubuntu. While running the program i need to take the output from the program and needs to save it in the log file. I use nohub to run them currently.when they fail I don't know why they fail.Then the process restart the nohub get overwritten . I want the process to restart and update the log file, I can check it at a later date. Currently I don't know the state of it, is it running or failed.

I heard that it is pretty easy to do it using python scripts . Anyone please help me to do this?

Thanks in advance Renjith Raj

Answer 1

You should use the subprocess module of python. If your logs are not too big, you can simply use :

# for python >=2.7
result = subprocess.check_output(["/path/to/process_to_lauch", "arg1"])
# for python < 2.7
process = subprocess.Popen(["/path/to/process_to_lauch", "arg1"], stdout=subprocess.PIPE, stderr=subprocess.PIPE)
str_out, str_errr = process.communicate()
# in str_out you will find the standard output of your process
# in str_err you will find the standard output of your process

But if your outputs are really big (let's talk in Mo, not in Ko), this may cause some memory overflow... In case of big output, use file handles for stdout and stderr:

out_file = open(out_file_name, "w")
err_file = open(out_file_name, "w")
process = subprocess.Popen(["/path/to/process_to_lauch", "arg1"], stdout=out_file, stderr=err_file)
return_code = process.wait()
out_file.close()
err_file.close()

And then, in out_file you'll find the output of the process, and in err_file the error output.

Of course, if you want to relaunch the process when it die, put this code in a loop ;)