Evaggelos Balaskas - System Engineer

I was suspicious with a cron entry on a new ubuntu server cloud vm, so I ended up to be looking on the logs.

Authentication token is no longer valid; new one required

After a quick internet search,

# chage -l root

Last password change                                    : password must be changed
Password expires                                        : password must be changed
Password inactive                                       : password must be changed
Account expires                                         : never
Minimum number of days between password change          : 0
Maximum number of days between password change          : 99999
Number of days of warning before password expires       : 7

due to the password must be changed on the root account, the cron entry does not run as it should.

This ephemeral image does not need to have a persistent known password, as the notes suggest, and it doesn’t! Even so, we should change to root password when creating the VM.

Ansible

Ansible have a password plugin that we can use with lookup.

TLDR; here is the task:

- name: Generate Random Password
    user:
      name: root
      password: "{{ lookup('password','/dev/null encrypt=sha256_crypt length=32') }}"

after ansible-playbook runs

# chage -l root

Last password change                                    : Mar 10, 2019
Password expires                                        : never
Password inactive                                       : never
Account expires                                         : never
Minimum number of days between password change          : 0
Maximum number of days between password change          : 99999
Number of days of warning before password expires       : 7

and cron entry now runs as it should.

Password Plugin

Let explain how password plugin works.

Lookup needs at-least two (2) variables, the plugin name and a file to store the output. Instead, we will use /dev/null not to persist the password to a file.

To begin with it, a test ansible playbook:

- hosts: localhost
  gather_facts: False
  connection: local

  tasks:
    - debug:
        msg: "{{ lookup('password', '/dev/null') }}"
      with_sequence: count=5

Output:

ok: [localhost] => (item=1) => {
    "msg": "dQaVE0XwWti,7HMUgq::"
}
ok: [localhost] => (item=2) => {
    "msg": "aT3zqg.KjLwW89MrAApx"
}
ok: [localhost] => (item=3) => {
    "msg": "4LBNn:fVw5GhXDWh6TnJ"
}
ok: [localhost] => (item=4) => {
    "msg": "v273Hbox1rkQ3gx3Xi2G"
}
ok: [localhost] => (item=5) => {
    "msg": "NlwzHoLj8S.Y8oUhcMv,"
}

Length

In password plugin we can also use length variable:

msg: "{{ lookup('password', '/dev/null length=32') }}"

output:

ok: [localhost] => (item=1) => {
    "msg": "4.PEb6ycosnyL.SN7jinPM:AC9w2iN_q"
}
ok: [localhost] => (item=2) => {
    "msg": "s8L6ZU_Yzuu5yOk,ISM28npot4.KwQrE"
}
ok: [localhost] => (item=3) => {
    "msg": "L9QvLyNTvpB6oQmcF8WVFy.7jE4Q1K-W"
}
ok: [localhost] => (item=4) => {
    "msg": "6DMH8KqIL:kx0ngFe8:ri0lTK4hf,SWS"
}
ok: [localhost] => (item=5) => {
    "msg": "ByW11i_66K_0mFJVB37Mq2,.fBflepP9"
}

Characters

We can define a specific type of python string constants

• ascii_letters (ascii_lowercase and ascii_uppercase
• ascii_lowercase
• ascii_uppercase
• digits
• hexdigits
• letters (lowercase and uppercase)
• lowercase
• octdigits
• punctuation
• printable (digits, letters, punctuation and whitespace
• uppercase
• whitespace

eg.

msg: "{{ lookup('password', '/dev/null length=32 chars=ascii_lowercase') }}"

ok: [localhost] => (item=1) => {
    "msg": "vwogvnpemtdobjetgbintcizjjgdyinm"
}
ok: [localhost] => (item=2) => {
    "msg": "pjniysksnqlriqekqbstjihzgetyshmp"
}
ok: [localhost] => (item=3) => {
    "msg": "gmeoeqncdhllsguorownqbynbvdusvtw"
}
ok: [localhost] => (item=4) => {
    "msg": "xjluqbewjempjykoswypqlnvtywckrfx"
}
ok: [localhost] => (item=5) => {
    "msg": "pijnjfcpjoldfuxhmyopbmgdmgdulkai"
}

Encrypt

We can also define the encryption hash. Ansible uses passlib so the unix active encrypt hash algorithms are:

• passlib.hash.bcrypt - BCrypt
• passlib.hash.sha256_crypt - SHA-256 Crypt
• passlib.hash.sha512_crypt - SHA-512 Crypt

eg.

msg: "{{ lookup('password', '/dev/null length=32 chars=ascii_lowercase encrypt=sha512_crypt') }}"

ok: [localhost] => (item=1) => {
    "msg": "$6$BR96lZqN$jy.CRVTJaubOo6QISUJ9tQdYa6P6tdmgRi1/NQKPxwX9/Plp.7qETuHEhIBTZDTxuFqcNfZKtotW5q4H0BPeN."
}
ok: [localhost] => (item=2) => {
    "msg": "$6$ESf5xnWJ$cRyOuenCDovIp02W0eaBmmFpqLGGfz/K2jd1FOSVkY.Lsuo8Gz8oVGcEcDlUGWm5W/CIKzhS43xdm5pfWyCA4."
}
ok: [localhost] => (item=3) => {
    "msg": "$6$pS08v7j3$M4mMPkTjSwElhpY1bkVL727BuMdhyl4IdkGM7Mq10jRxtCSrNlT4cAU3wHRVxmS7ZwZI14UwhEB6LzfOL6pM4/"
}
ok: [localhost] => (item=4) => {
    "msg": "$6$m17q/zmR$JdogpVxY6MEV7nMKRot069YyYZN6g8GLqIbAE1cRLLkdDT3Qf.PImkgaZXDqm.2odmLN8R2ZMYEf0vzgt9PMP1"
}
ok: [localhost] => (item=5) => {
    "msg": "$6$tafW6KuH$XOBJ6b8ORGRmRXHB.pfMkue56S/9NWvrY26s..fTaMzcxTbR6uQW1yuv2Uy1DhlOzrEyfFwvCQEhaK6MrFFye."
}