新しく借用したサーバーの初期設定を終えた後の動作確認でMuninのグラフが表示されず404となりました。
systemctl start muninに失敗しています。
[root@local_2 munin]# systemctl status munin
● munin.service - Munin server to collect data from nodes
   Loaded: loaded (/usr/lib/systemd/system/munin.service; static; vendor preset: disabled)
   Active: failed (Result: exit-code) since Sat 2020-10-17 15:55:01 JST; 3min 41s ago
     Docs: man:munin-cron(8)
  Process: 75089 ExecStart=/usr/bin/munin-cron (code=exited, status=1/FAILURE)
 Main PID: 75089 (code=exited, status=1/FAILURE)

10月 17 15:55:00 local_2 systemd[1]: Started Munin server to collect data from nodes.
10月 17 15:55:01 local_2 munin-cron[75089]: [FATAL] There is nothing to do here, since there are no nodes with any plugins.  Please refer to http://munin-monitoring.org/wiki/FAQ_no_graphs at /usr/share/munin/munin-html line 38.
10月 17 15:55:01 local_2 systemd[1]: munin.service: Main process exited, code=exited, status=1/FAILURE
10月 17 15:55:01 local_2 systemd[1]: munin.service: Failed with result 'exit-code'.
http://munin-monitoring.org/wiki/FAQ_no_graphs
を参照すると
# su - munin --shell=/bin/bash
$ /usr/share/munin/munin-update --nofork --debug
を実行して出力されるメッセージを確認する手順が書かれているので確認します。
[munin@local_2 ~]$ /usr/share/munin/munin-update --nofork --debug
2020/10/17 15:59:40 [DEBUG] Creating new lock file /var/run/munin/munin-update.lock
2020/10/17 15:59:40 [DEBUG] Creating lock : /var/run/munin/munin-update.lock succeeded
2020/10/17 15:59:40 [INFO]: Starting munin-update
2020/10/17 15:59:40 [DEBUG] Creating new lock file /var/run/munin/munin-localhost-localhost.lock
2020/10/17 15:59:40 [DEBUG] Creating lock : /var/run/munin/munin-localhost-localhost.lock succeeded
2020/10/17 15:59:40 [DEBUG] Reading state for localhost-localhost in /var/lib/munin/state-localhost-localhost.storable
2020/10/17 15:59:40 [INFO] starting work in 75694 for localhost/127.0.0.1:4949.
2020/10/17 15:59:40 [INFO] node localhost advertised itself as local_2 instead.
2020/10/17 15:59:40 TLS set to "disabled".
2020/10/17 15:59:40 [DEBUG] Negotiating capabilities
2020/10/17 15:59:40 [DEBUG] Writing to socket: "cap multigraph dirtyconfig
".
2020/10/17 15:59:40 [DEBUG] Node says /cap multigraph dirtyconfig/
2020/10/17 15:59:40 [DEBUG] Writing to socket: "list local_2
".
2020/10/17 15:59:40 [WARNING] Config node localhost listed no services for local_2, (advertised as local_2).  Please see http://munin-monitoring.org/wiki/FAQ_no_graphs for further information.
新しく設定したサーバーのホスト名は「local_2」です。
muninが監視するのは127.0.0.1(localhost)としていますが、local_2が127.0.0.1としてリストアップされていないとのことです。
http://munin-monitoring.org/wiki/FAQ_no_graphs
の手順にしたがって、/etc/hostsを修正します。
[munin@local_2 ~]$ cat /etc/hosts
127.0.0.1   localhost local_2
無事、グラフが表示されるようなりました。