Creating a user with random password using Ansible

So I need to create an user in a machine so I can then have a script that will log into this machine and backup its database. Which database is that, you might ask? For this discussion it does not matter besides that it is running in a Linux box. But, if you want a more specific example, we could be backing up a sqlite database since we talked about how to do the deed before.

Anyway, the plan is to have the script ssh into the database server and grab the backup. Since we are using ssh in the script, we might as well use key pair authentication. Now I have learned that by default if you create a user and do not assign it a password, you will not be able to login as said user using key pair authentication. You can turn that off but I would rather not. Instead, since I am creating said user programmatically, I can give it a long random password.

Now that we have a plan, let's see how to do it in an ansible playbook. I will present only the relevant bits since I do not know how you do your playbooks. So, we could create a user using something like

- name: Create user_name
    user:
      name={{user_name}}
      groups={{user_groups}}
      shell=/bin/bash
      state=present
      append=yes

which would create user user_name who will also belong to the groups defined in user_groups, where user_name and user_groups are variables defined somewhere earlier in the show. And this would create a user without a password, which would do us no good. Nor would us make the playbook stop and ask us to enter a password. We said earlier we are going to create a random password, so let's see if we can make something random enough for our needs.

I plan on generating this random password in the machine we are running ansible on, not the target machine. One of the reasons is that I want to use the Linux command mkpassword to create the password hash (note it is being called using the shell command. So, I will use a local_action to do the deed. For instance, let's say I want the password to be pickles and encoded using SHA-512 hash (mild encryption). I could accomplish it by writing

- name: generate random password for new user
    local_action: shell  mkpasswd --method=SHA-512 pickles
    register: user_pw

This would create a hash, say

$6$rIcep9bGJTUpE$s8pka1dX6gWfyeNfi8YLaqrg/85tgtpJv809AUmO2jHhMQbSUnuNSloJSa6EmOQS02Ek4mvpiIu2DAvA9W0UL0

and assign it to the variable user_pw. This of course has to be done before the user is created. To use it with our new user, we can then modify our little user creation function to something like this:

- name: Create user_name
    user:
      name={{user_name}}
      groups={{user_groups}}
      shell=/bin/bash
      state=present
      append=yes
      update_password=on_create
      password="{{user_pw.stdout}}"

In the last line we are feeding the value of user_pw, user_pw.stdout, to password. But why can't I just feed user_pw? Here's an exercise to you: tell your playbook just print user_pw. Doesn't it look very object-like?

If you run your playbook and all went well, go to the target machine and check if there is a password associated with the user in /etc/shadow. If the user was already created, you will need to delete user and let ansible recreate it.

So we have so far created a way to create a password hash and then create a new user with that password. The last step we need is to make the password random. Here is what I am proposing: how about if we use date since epoch in seconds as our password and then mangle it a bit? Here is a simple mangling example:

raub@desktop:~$ date +%s
1479095572
raub@desktop:~$ date +%s | sha384sum
3d47137f4cd6bfb638deecc661b4e0ae9545ab2454b20eac51b6992807b3f518a49be9ef3b72a5abdc9167e32acc2473  -
raub@desktop:~$ date +%s | sha384sum | md5sum
65db8ecf178a505ea17e9b53cc5adf31  -
raub@desktop:~$ date +%s | sha384sum | md5sum | cut -f 1 -d ' '
b8a49ccaa4721877cf39e510c7ac3622
raub@desktop:~$

Which gives b8a49ccaa4721877cf39e510c7ac3622 as the output, which should be long enough to fulfill our needs. Of course if you run it again, it will spit out a different result, which is what we want? Perfectly random? Not by a long shot, but it is long enough for our needs. Remember: there is nothing saying you have to use the above. Hav efun creating your own function!

So, let's apply that to our little password generating function:

- name: generate random password for new user
    local_action: shell  mkpasswd --method=SHA-512 $(date +%s | sha384sum | md5sum | cut -f 1 -d ' ')
    register: user_pw

And we should be good to go. Here is how the final version should look like in a playbook:

- name: generate random password for new user
    local_action: shell  mkpasswd --method=SHA-512 $(date +%s | sha384sum | md5sum | cut -f 1 -d ' ')
    register: user_pw
# Something might happen here before we create user
- name: Create user_name
    user:
      name={{user_name}}
      groups={{user_groups}}
      shell=/bin/bash
      state=present
      append=yes
      update_password=on_create
      password="{{user_pw.stdout}}"

Now we have an user, we can then create the ssh key pair we talked about in an earlier article. Of course we might edit the ./ssh/authorized_keys file to restrict what that key can do.