I’m using Ansible to manage …

I’m using Ansible to manage a small fleet of Raspberry Pis. I’d been using the copy module to set a value in /sys:

- name: Enable compressed swap now (with zsmalloc)
  become: true
  ansible.builtin.copy:
    content: zsmalloc
    dest: /sys/module/zswap/parameters/zpool
    unsafe_writes: true

But that always reports that the file changed, even if it already had that value. Today I got the lineinfile module to update the value. This only says the value changed when it actually did:

- name: Enable compressed swap now (with zsmalloc)
  become: true
  ansible.builtin.lineinfile:
    path: /sys/module/zswap/parameters/zpool
    regexp: "^(?!zsmalloc).*$"
    line: zsmalloc
    unsafe_writes: true

Since these “files” only have one line, this uses regexp to see if that line already matches the expected value. If so, it moves on. If not, it writes the new value.

Note: unsafe_writes: true is there because you can’t write arbitrary filenames into /sys and then mv them into place. You have to write directly to the target “file”.

Related