[python] Using sudo with Python script

I'm trying to write a small script to mount a VirtualBox shared folder each time I execute the script. I want to do it with Python, because I'm trying to learn it for scripting.

The problem is that I need privileges to launch mount command. I could run the script as sudo, but I prefer it to make sudo by its own.

I already know that it is not safe to write your password into a .py file, but we are talking about a virtual machine that is not critical at all: I just want to click the .py script and get it working.

This is my attempt:

#!/usr/bin/env python
import subprocess

sudoPassword = 'mypass'
command = 'mount -t vboxsf myfolder /home/myuser/myfolder'

subprocess.Popen('sudo -S' , shell=True,stdout=subprocess.PIPE)
subprocess.Popen(sudoPassword , shell=True,stdout=subprocess.PIPE)
subprocess.Popen(command , shell=True,stdout=subprocess.PIPE)

My python version is 2.6

Many answers focus on how to make your solution work, while very few suggest that your solution is a very bad approach. If you really want to "practice to learn", why not practice using good solutions? Hardcoding your password is learning the wrong approach!

If what you really want is a password-less mount for that volume, maybe sudo isn't needed at all! So may I suggest other approaches?

• Use /etc/fstab as mensi suggested. Use options user and noauto to let regular users mount that volume.

• Use Polkit for passwordless actions: Configure a .policy file for your script with <allow_any>yes</allow_any> and drop at /usr/share/polkit-1/actions

• Edit /etc/sudoers to allow your user to use sudo without typing your password. As @Anders suggested, you can restrict such usage to specific commands, thus avoiding unlimited passwordless root priviledges in your account. See this answer for more details on /etc/sudoers.

All the above allow passwordless root privilege, none require you to hardcode your password. Choose any approach and I can explain it in more detail.

As for why it is a very bad idea to hardcode passwords, here are a few good links for further reading:

• Why You Shouldn’t Hard Code Your Passwords When Programming
• How to keep secrets secret (Alternatives to Hardcoding Passwords)
• What's more secure? Hard coding credentials or storing them in a database?
• Use of hard-coded credentials, a dangerous programming error: CWE
• Hard-coded passwords remain a key security flaw

It works in python 2.7 and 3.8:

from subprocess import Popen, PIPE
from shlex import split

proc = Popen(split('sudo -S %s' % command), bufsize=0, stdout=PIPE, stdin=PIPE, stderr=PIPE)
proc.stdin.write((password +'\n').encode()) # write as bytes
proc.stdin.flush() # need if not bufsize=0 (unbuffered stdin)

without .flush() password will not reach sudo if stdin buffered. In python 2.7 Popen by default used bufsize=0 and stdin.flush() was not needed.

For secure using, create password file in protected directory:

mkdir --mode=700 ~/.prot_dir
nano ~/.prot_dir/passwd.txt
chmod 600 ~/.prot_dir/passwd.txt 

at start your py-script read password from ~/.prot_dir/passwd.txt

with open(os.environ['HOME'] +'/.prot_dir/passwd.txt') as f:
    password = f.readline().rstrip()

Please try module pexpect. Here is my code:

import pexpect
remove = pexpect.spawn('sudo dpkg --purge mytool.deb')
remove.logfile = open('log/expect-uninstall-deb.log', 'w')
remove.logfile.write('try to dpkg --purge mytool\n')
if remove.expect(['(?i)password.*']) == 0:
    # print "successfull"
    remove.sendline('mypassword')
    time.sleep(2)
    remove.expect(pexpect.EOF,5)
else:
    raise AssertionError("Fail to Uninstall deb package !")

subprocess.Popen creates a process and opens pipes and stuff. What you are doing is:

• Start a process sudo -S
• Start a process mypass
• Start a process mount -t vboxsf myfolder /home/myuser/myfolder

which is obviously not going to work. You need to pass the arguments to Popen. If you look at its documentation, you will notice that the first argument is actually a list of the arguments.

To limit what you run as sudo, you could run

python non_sudo_stuff.py
sudo -E python -c "import os; os.system('sudo echo 1')"

without needing to store the password. The -E parameter passes your current user's env to the process. Note that your shell will have sudo priveleges after the second command, so use with caution!

I know it is always preferred not to hardcode the sudo password in the script. However, for some reason, if you have no permission to modify /etc/sudoers or change file owner, Pexpect is a feasible alternative.

Here is a Python function sudo_exec for your reference:

import platform, os, logging
import subprocess, pexpect

log = logging.getLogger(__name__)

def sudo_exec(cmdline, passwd):
    osname = platform.system()
    if osname == 'Linux':
        prompt = r'\[sudo\] password for %s: ' % os.environ['USER']
    elif osname == 'Darwin':
        prompt = 'Password:'
    else:
        assert False, osname

    child = pexpect.spawn(cmdline)
    idx = child.expect([prompt, pexpect.EOF], 3)
    if idx == 0: # if prompted for the sudo password
        log.debug('sudo password was asked.')
        child.sendline(passwd)
        child.expect(pexpect.EOF)
return child.before

• Use -S option in the sudo command which tells to read the password from 'stdin' instead of the terminal device.

• Tell Popen to read stdin from PIPE.

• Send the Password to the stdin PIPE of the process by using it as an argument to communicate method. Do not forget to add a new line character, '\n', at the end of the password.

sp = Popen(cmd , shell=True, stdin=PIPE)
out, err = sp.communicate(_user_pass+'\n')   

To pass the password to sudo's stdin:

#!/usr/bin/env python
from subprocess import Popen, PIPE

sudo_password = 'mypass'
command = 'mount -t vboxsf myfolder /home/myuser/myfolder'.split()

p = Popen(['sudo', '-S'] + command, stdin=PIPE, stderr=PIPE,
          universal_newlines=True)
sudo_prompt = p.communicate(sudo_password + '\n')[1]

Note: you could probably configure passwordless sudo or SUDO_ASKPASS command instead of hardcoding your password in the source code.

I used this for python 3.5. I did it using subprocess module.Using the password like this is very insecure.

The subprocess module takes command as a list of strings so either create a list beforehand using split() or pass the whole list later. Read the documentation for moreinformation.

#!/usr/bin/env python
import subprocess

sudoPassword = 'mypass'
command = 'mount -t vboxsf myfolder /home/myuser/myfolder'.split()

cmd1 = subprocess.Popen(['echo',sudoPassword], stdout=subprocess.PIPE)
cmd2 = subprocess.Popen(['sudo','-S'] + command, stdin=cmd1.stdout, stdout=subprocess.PIPE)

output = cmd2.stdout.read.decode()

sometimes require a carriage return:

os.popen("sudo -S %s"%(command), 'w').write('mypass\n')