The sample code for executing a command without `sudo` but `su -c`.

fabfile.py

import os
from fabric.api import env, puts, sudo, settings
from fabric.colors import cyan

DOMAIN_LIST = '%s/.ssh/config' %  os.environ['HOME']

env.use_ssh_config = True
env.disable_known_hosts = True
env.password = 'xxxxxx'

def set_all_hosts():
    with open(DOMAIN_LIST) as f:
        all_hosts = map(lambda y: y.split()[1],
          filter(lambda x: x.startswith('Host'), f.read().splitlines()))

    env.hosts = all_hosts
        
    puts(cyan('env.hosts = %s' % all_hosts))

def sudo_command(cmd):
    with settings(sudo_prefix='su -c ', sudo_prompt='Password: '):
        sudo(cmd)

$ fab -H host1 sudo_command:'head /etc/shadow'
or
$ fab set_all_hosts sudo_command:'head /etc/shadow'