Ansible error on shell command returning zero

Question

Ansible doesn't seem to be able to handle the result '0' for shell commands. This

- name: Check if swap exists
  shell: "swapon -s | grep -ci dev"
  register: swap_exists

Returns an error

"msg": "non-zero return code"

But when I replace "dev" with "type", which actually always occurs and gives a count of at least 1, then the command is successful and no error is thrown.

I also tried with command: instead of shell: - it doesn't give an error, but then the command is also not executed.

ilias-sp · Accepted Answer · 2018-05-21 00:47:16Z

36

since you want to run a sequence of commands that involve pipe, ansible states you should use shell and not command, as you are doing.

So, the problem is the fact that grep returns 1 (didnt find a match on the swapon output), and ansible considers this a failure. Since you are well sure there is no issue, just add a ignore_errors: true and be done with it.

- name: Check if swap exists
  shell: "swapon -s | grep -ci non_existent_string"
  register: swap_exists
  ignore_errors: true

OR:

if you want to narrow it down to return codes 0 and 1, instruct ansible to not consider failures those 2 rcs:

- name: Check if swap exists
  shell: "swapon -s | grep -ci non_existent_string"
  register: swap_exists
  # ignore_errors: true
  failed_when: swap_exists.rc != 1 and swap_exists.rc != 0

answered May 21, 2018 at 0:47

ilias-sp

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3 Comments

user2066480 Over a year ago

Your answer is good in a strict way, and a good learning example. But for what I'm trying to do, realizing that there is the 'ansible fact' ansible_swaptotal_mb that immediately indicates whether there is a swap in the system or not, actually points to a better solution :)

ilias-sp Over a year ago

i agree, i would prefer the ansible facts too if they can provide me the information i need :)

Nicola Over a year ago

I believe that failed_when: is much better than ignore_errors: true! Thanks :)

Calum Halpin · Accepted Answer · 2020-02-23 20:31:15Z

2

I found a better way. if you only need to know the record number this works:

- name: Check if swap exists
  shell: "swapon -s | grep -i dev|wc -l"
  register: swap_exists

Another way is to always use cat at the end of the pipe. See Ansible shell module returns error when grep results are empty

    - name: Check if swap exists
      shell: "swapon -s | grep -i dev|cat"
      register: swap_exists

edited Feb 23, 2020 at 20:31

Calum Halpin

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answered Feb 23, 2020 at 9:20

robin

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Comments

Aravinthan K · Accepted Answer · 2020-06-17 05:15:48Z

0

You can also parse the grep count result in awk and return your custom output. This will avoid the ignore_errors module.

- name: Check if swap exists
  shell: "swapon -s | grep -ci dev" | awk '{ r = $0 == 0 ? "false":"true"; print r }'
  register: swap_exists

answered Jun 17, 2020 at 5:15

Aravinthan K

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