+++ This bug was initially created as a clone of Bug #1741806 +++

Description of problem:
Starting the dnsmasq.service, when port 53 is already used by another process, the command is returning exitvalue 0 and failing silently.

Version-Release number of selected component (if applicable):
dnsmasq-2.76-9.el7.x86_64

How reproducible:
always

Steps to Reproduce:
1. Install RHEL 7.6
2. yum install dnsmasq -y
3. python -m SimpleHTTPServer 53
4. systemctl start dnsmasq

Actual results:
Service fail to start silently. No output shown

Expected results:
# systemctl start dnsmasq
Job for dnsmasq.service failed because the control process exited with error code. See "systemctl status dnsmasq.service" and "journalctl -xe" for details.


Additional info:
[root@localhost ~]# systemctl start dnsmasq
[root@localhost ~]# echo $?
0
[root@localhost ~]# systemctl start httpd                                                                              
Job for httpd.service failed because the control process exited with error code. See "systemctl status httpd.service" and "journalctl -xe" for details.
[root@localhost ~]# echo $?                                                                                            
1

--- Additional comment from Petr Menšík on 2019-08-23 17:06:15 CEST ---

It is visible in systemctl dnsmasq status. But I admit that is not great way to check it.

It would require change of systemd service unit from Type=simple to forking or notify. Both implement status check and report if daemon fails.

I think notify is better alternative for systemd services is Type=notify, but no support for it exists in upstream. It should change way it switches to unprivileged user if abrt catching of core dumps should not break.
dnsmasq forks already second process, but not in way that can be reused for checking status on startup. Might be a little easier, but I think it is already considered superseded by notify. This is also not supported in current code.
Either way requires new code for reporting failure before serving requests.