Today I met a thing that I never have met. When I need to restart my server, I use the "restart server" button on my aapanel, however, after that, I cannot visit my aapanel again, that means, I cannot open the url of aapanel any more:
This site can’t be reached xx.xxx.xx.xx refused to connect.
Try:

Checking the connection
Checking the proxy and the firewall
ERR_CONNECTION_REFUSED

I have checked the logs and I find that this may be the errors from nginx: [root@aws ~]# sudo ss -tuln | grep -E ':80|:443|:888'
tcp LISTEN 0 128 *:80 :
tcp LISTEN 0 128 *:888 :
tcp LISTEN 0 128 *:443 :
[root@aws ~]# sudo systemctl start nginx
Job for nginx.service failed because the control process exited with error code. See "systemctl status nginx.service" and "journalctl -xe" for details.
[root@aws ~]# ^C
[root@aws ~]# sudo systemctl status nginx.service
● nginx.service - LSB: starts the nginx web server
Loaded: loaded (/etc/rc.d/init.d/nginx; bad; vendor preset: disabled)
Active: failed (Result: exit-code) since Thu 2023-07-06 15:31:30 UTC; 1min 22s ago
Docs: man:systemd-sysv-generator(8)
Process: 20895 ExecStart=/etc/rc.d/init.d/nginx start (code=exited, status=1/FAILURE)

Jul 06 15:31:30 vultr.guest systemd[1]: Starting LSB: starts the nginx web s....
Jul 06 15:31:30 vultr.guest nginx[20895]: Starting nginx... nginx (pid 20804....
Jul 06 15:31:30 vultr.guest systemd[1]: nginx.service: control process exite...1
Jul 06 15:31:30 vultr.guest systemd[1]: Failed to start LSB: starts the ngin....
Jul 06 15:31:30 vultr.guest systemd[1]: Unit nginx.service entered failed state.
Jul 06 15:31:30 vultr.guest systemd[1]: nginx.service failed.
Hint: Some lines were ellipsized, use -l to show in full.
[root@aws ~]# sudo journalctl -u nginx.service
-- Logs begin at Thu 2023-07-06 12:10:39 UTC, end at Thu 2023-07-06 15:33:01 UTC
Jul 06 12:10:52 vultr.guest systemd[1]: Starting LSB: starts the nginx web serve
Jul 06 12:10:52 vultr.guest nginx[1287]: Starting nginx... nginx: [emerg] mkdir(
Jul 06 12:10:52 vultr.guest nginx[1287]: failed
Jul 06 12:10:52 vultr.guest systemd[1]: nginx.service: control process exited, c
Jul 06 12:10:52 vultr.guest systemd[1]: Failed to start LSB: starts the nginx we
Jul 06 12:10:52 vultr.guest systemd[1]: Unit nginx.service entered failed state.
Jul 06 12:10:52 vultr.guest systemd[1]: nginx.service failed.
Jul 06 12:58:23 vultr.guest systemd[1]: Starting LSB: starts the nginx web serve
Jul 06 12:58:23 vultr.guest nginx[31968]: Starting nginx... nginx (pid 31777 317
Jul 06 12:58:23 vultr.guest systemd[1]: nginx.service: control process exited, c
Jul 06 12:58:23 vultr.guest systemd[1]: Failed to start LSB: starts the nginx we
Jul 06 12:58:23 vultr.guest systemd[1]: Unit nginx.service entered failed state.
Jul 06 12:58:23 vultr.guest systemd[1]: nginx.service failed.
Jul 06 13:03:11 vultr.guest systemd[1]: Starting LSB: starts the nginx web serve
Jul 06 13:03:11 vultr.guest nginx[15571]: Starting nginx... nginx (pid 15371 153
Jul 06 13:03:11 vultr.guest systemd[1]: nginx.service: control process exited, c
Jul 06 13:03:11 vultr.guest systemd[1]: Failed to start LSB: starts the nginx we
Jul 06 13:03:11 vultr.guest systemd[1]: Unit nginx.service entered failed state.
Jul 06 13:03:11 vultr.guest systemd[1]: nginx.service failed.
Jul 06 13:05:18 vultr.guest systemd[1]: Starting LSB: starts the nginx web serve
Jul 06 13:05:18 vultr.guest nginx[22493]: Starting nginx... nginx (pid 22371 223
Jul 06 13:05:18 vultr.guest systemd[1]: nginx.service: control process exited, c
lines 1-23 But the problem is that i always cannot restart the nginx. Even sometimes I can restart the nginx, I still cannot visit my aapanel. And, all of my websites on the panel cannot be visited normally. Sometimes, some websites cannot be opened with a 520 error, sometimes, the home page can be opened, but the inner pages cannot be opened, and shows 521 error. Actually I have done nothing and just restart the server and then everything has changed. Could you check and tell me how to solve this problem?