Change Unix password from command line over Python/Fabric

Question

I would like a way to update my password on a remote Ubuntu 10.4 box with fabric.

I would expect my fabfile.py would look something like this:

def update_password(old_pw, new_pw):
    # Connects over ssh with a public key authentication
    run("some_passwd_cmd --old %s --new %s" % (old_pw, new_pd))

Unfortunately the only command I know of that lets one change the password is passwd, and on Ubuntu 10.4 there doesn't seem to be any way to pass in the new (or old) password as an argument to passwd.

What command could one use to change a user's password on Ubuntu 10.4 via fabric?

EDIT: I've had a look at usermod -p, and that may work but it isn't recommended by the man page.

EDIT: For some reason usermod -p wasn't working either over fabric.

As well, I've tried a (somewhat insecure) variation on mikej's answer that did solve the problem:

# connecting & running as root.
from fabric.api import *
from fabric.contrib import files

files.append("%s\n%s" % (passwd, passwd), '.pw.tmp')
# .pw.tmp:
# PASSWD
# PASSWD

run("passwd %s < .pw.tmp" % user)

run("rm .pw.tmp")

It's not a very elegant solution, but it works.

Thank you for reading.

Brian

Answer 1

You could feed the new and old passwords into passwd using echo e.g.

echo -e "oldpass\\nnewpass\\nnewpass" | passwd

(the -e option for echo enables interpretation of backslash escapes so the newlines are interpreted as such)

Answer 2

The trick is to use a combination of usermod and Python’s crypt to change your password:

from crypt import crypt
from getpass import getpass
from fabric.api import *

def change_password(user):
    password = getpass('Enter a new password for user %s:' % user)
    crypted_password = crypt(password, 'salt')
    sudo('usermod --password %s %s' % (crypted_password, user), pty=False)