How can we change the default location of osquery_result.log file on fleet server. The default location as of now is "/tmp" can we change is it to something else?

Look at the logging options documented in https://github.com/kolide/fleet/blob/master/docs/infrastructure/configuring-the-fleet-binary.md

apiVersion: v1 kind: option spec: config: decorators: load: - SELECT uuid AS host_uuid FROM system_info; - SELECT hostname AS hostname FROM system_info; file_paths: homes: - /home/%% etc: - /etc/%% file_accesses: - home - etc osquery: result_log_file: - /var/log/osquery/result.log options: disable_distributed: false distributed_interval: 10 distributed_plugin: tls distributed_tls_max_attempts: 3 logger_plugin: tls logger_tls_endpoint: /api/v1/osquery/log logger_tls_period: 10 pack_delimiter: / overrides: {}

No, you need to set it in the configuration you start the Fleet server with.

Is there any way to check config file for syntax errors? before I apply the config file to fleet.

For the Fleet server configuration you can use the

fleet config_dump

command along with any flags you'd provide to

fleet serve

to check that you get the expected configuration.