[PR #12014/b8659f5c backport][stable-12] pam_limits: only create backup file when content actually changes (#12020)

pam_limits: only create backup file when content actually changes (#12014)

* fix(pam_limits): only create backup when file is actually changed

Fixes #12011



* changelog: add fragment for PR 12014



---------


(cherry picked from commit b8659f5c61)

Co-authored-by: Alexei Znamensky <103110+russoz@users.noreply.github.com>
Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

changelogs/fragments/12014-pam_limits-backup.yml

@@ -0,0 +1,2 @@
+bugfixes:
+  - "pam_limits - only create backup file when the target file is actually modified (https://github.com/ansible-collections/community.general/issues/12011, https://github.com/ansible-collections/community.general/pull/12014)."

plugins/modules/pam_limits.py

@@ -235,10 +235,7 @@ def main():
 
     _assert_is_valid_value(module, limit_item, value)
 
-    # Backup
-    if backup:
-        backup_file = module.backup_local(limits_conf)
-
+    backup_file = None
     space_pattern = re.compile(r"\s+")
 
     if does_not_exist:
@@ -356,6 +353,9 @@ def main():
             with open(limits_conf, "a"):
                 pass
 
+        if backup and changed and not does_not_exist:
+            backup_file = module.backup_local(limits_conf)
+
         # Move tempfile to newfile
         module.atomic_move(os.path.abspath(nf.name), os.path.abspath(limits_conf))
 
@@ -370,7 +370,7 @@ def main():
         diff=dict(before=b"".join(lines), after=content_new),
     )
 
-    if backup:
+    if backup_file:
         res_args["backup_file"] = backup_file
 
     module.exit_json(**res_args)