>>> On 4/1/2011 at 07:33 AM, Kushal Kumaran <kushal.kumaran+pyt...@gmail.com> wrote: > On Fri, Apr 1, 2011 at 4:31 AM, Adriaan Renting <rent...@astron.nl> wrote: >> L.S. >> >> I have a problem that a background process that I'm trying to start with >> subprocess.Popen gets interrupted and starts waiting for input no matter >> what I try to do to have it continue to run. It happens when I run it >> with nohup in the background. >> I've tried to find a solution searching the internet, but found none. >> I've written a small test script that reproduces the problem and hope >> maybe here there is someone who can tell me what's going wrong. Any >> suggestions are welcome. >> >> (renting)myhost> cat test.py >> #!/usr/bin/python >> # script to test subprocess problem >> import subprocess, sys, time >> >> for f in range(3): >> command = ["ssh", "-T", "localhost", "uptime"] >> comm = subprocess.Popen(command, shell=False, stdin=None, >> stdout=subprocess.PIPE, stderr=subprocess.STDOUT, close_fds=True) >> print '1' >> if comm.returncode: >> print "error: %i" % (comm.return_code) >> else: >> print '2' >> (output, output2) = comm.communicate(input=None) >> print output >> print output2 >> print '3' >> time.sleep(3) >> >> (renting)myhost> python --version >> Python 2.5.2 >> >> (renting)myhost> nohup ./test.py -O2 & >> [1] 15679 >> >> (renting)myhost> 1 >> 2 >> 22:40:30 up 24 days, 7:32, 1 user, load average: 0.00, 0.00, 0.00 >> >> None >> 3 >> 1 >> 2 >> >> [1] + Suspended (tty input) ./test.py -O2 >> (renting)myhost> fg >> ./test.py -O2 >> >> 22:40:35 up 24 days, 7:32, 1 user, load average: 0.00, 0.00, 0.00 >> >> None >> 3 >> 1 >> 2 >> 22:40:56 up 24 days, 7:32, 1 user, load average: 0.00, 0.00, 0.00 >> >> None >> 3 >> >> (renting)myhost> >> >> Now as you can see, it suspends on the second time through the for loop, >> until I bring it to the foreground and hit . >> What you don't see, is that I make it do this by pushing the arrow keys >> a couple of times. The same happens when I would exit the shell, despite >> it running with nohup. >> I don't need to exit to make it suspend, any combination of a few random >> keystrokes makes it do this. It seems depending on the timing though, >> during the sleep(3) it seems to ignore me, only when subprocess is >> actually running will it suspend if I generate keystrokes. >> If the ssh command is executed without -T option it suspends directly, >> so I think it's related to the ssh command. I log in with a >> public/private key pair to avoid having to enter a password. >> >> Any suggestions are welcome, >> > > What operating system is this? Try with stdin=open(os.devnull, 'rb') > to the Popen call instead. Also, this seems to be similar: > http://stackoverflow.com/questions/1365653/calling-fgets-on-popen-of-ssh-is- > flushing-the-beginning-of-stdin-of-the-cal > > The "Suspended (tty input)" message means that a background process > tried to read from stdin, so got suspended. This is part of the job > control mechanism. > > -- > regards, > kushal
This solves the problem using stdin=open(os.devnull, 'rb') instead of stdin=None makes it run even if there is input from stdin in the foreground process. The operating system is Ubuntu 8.04 I understood what Suspended (tty input) means. I don't understand why it waits for input if stdin=None. Thank you for your help. Adriaan Renting. -- http://mail.python.org/mailman/listinfo/python-list
