从crontab运行时subprocess.popen似乎失败

Question

I'm running a script from crontab that will just ssh and run a command and store the results in a file.

The function that seems to be failing is subprocess.popen .

Here is the python function:

def _executeSSHCommand(sshcommand,user,node):

    '''
    Simple function to execute an ssh command on a remote node.
    '''

    sshunixcmd = '/usr/bin/ssh %s@%s \'%s\'' % (user,node,sshcommand)
    process = subprocess.Popen([sshunixcmd],
                                shell=True,
                                stdout=subprocess.PIPE,
                                stderr=subprocess.PIPE)
    process.wait()
    result = process.stdout.readlines()
    return result

When it's run from the command line, it executes correctly, from cron it seems to fail with the error message below.

Here are the crontab entries:

02 * * * * /home/matt/scripts/check-diskspace.py >> /home/matt/logs/disklog.log

Here are the errors:

Sep 23 17:02:01 timmy CRON[13387]: (matt) CMD (/home/matt/scripts/check-diskspace.py >> /home/matt/logs/disklog.log)
Sep 23 17:02:01 timmy CRON[13386]: (CRON) error (grandchild #13387 failed with exit status 2)

I'm going blind trying to find exactly where I have gone so wrong. Any ideas?

Answer 1

The cron PATH is very limited. You should either set absolute path to your ssh /usr/bin/ssh or set the PATH as a first line in your crontab.

Answer 2

You probably need to pass ssh the -i argument to tell ssh to use a specific key file. The problem is that your environment is not set up to tell ssh which key to use.

The fact that you're using python here is a bit of a red herring.

Answer 3

For everything ssh-related in python, you might consider using paramiko . Using it, the following code should do what you want.

import paramiko
client = paramiko.SSHClient()
client.load_system_host_keys()
client.connect(node, username=user)
stdout = client.exec_command(ssh_command)[0]
return stdout.readlines()

Answer 4

When running python scripts from cron, the environment PATH can be a hangup, as user1652558 points out.

To expand on this answer with example code to add custom PATH values to the environment for a subprocess call:

import os
import subprocess

#whatever user PATH values you need
my_path = "/some/custom/path1:/some/custom/path2"

#append the custom values to the current PATH settings
my_env = os.environ.copy()
my_env["PATH"] = my_path + ":" + my_env["PATH"]

#subprocess call
resp = subprocess.check_output([cmd], env=my_env, shell=True)