====== Fedora 29 のKVM仮想マシンで Failed to start Network Manager Wait Online. が発生する ======
NetworkManager-wait-online サービスは、設定されているタイムアウト(--timeout=30 秒)を超えても NetworkManager の準備が完了していない場合にこのエラーを出力する。\\
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<code>
$ systemctl status NetworkManager-wait-online.service
● NetworkManager-wait-online.service - Network Manager Wait Online
   Loaded: loaded (/usr/lib/systemd/system/NetworkManager-wait-online.service; enabled; vendor preset: enabled)
   Active: failed (Result: exit-code) since Tue 2019-01-22 23:23:30 JST; 5min ago
     Docs: man:nm-online(1)
  Process: 483 ExecStart=/usr/bin/nm-online -s -q --timeout=30 (code=exited, status=1/FAILURE)
 Main PID: 483 (code=exited, status=1/FAILURE)

 1月 22 23:23:00 black-vps001 systemd[1]: Starting Network Manager Wait Online...
 1月 22 23:23:30 black-vps001 systemd[1]: NetworkManager-wait-online.service: Main process exited, code=exited, status=1/FAILURE
 1月 22 23:23:30 black-vps001 systemd[1]: NetworkManager-wait-online.service: Failed with result 'exit-code'.
 1月 22 23:23:30 black-vps001 systemd[1]: Failed to start Network Manager Wait Online.
</code>
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しかし、再度開始すると正常起動する。\\
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<code>
$ sudo systemctl start NetworkManager-wait-online.service
$ systemctl status NetworkManager-wait-online.service
● NetworkManager-wait-online.service - Network Manager Wait Online
   Loaded: loaded (/usr/lib/systemd/system/NetworkManager-wait-online.service; enabled; vendor preset: enabled)
   Active: active (exited) since Tue 2019-01-22 23:32:09 JST; 5s ago
     Docs: man:nm-online(1)
  Process: 1236 ExecStart=/usr/bin/nm-online -s -q --timeout=30 (code=exited, status=0/SUCCESS)
 Main PID: 1236 (code=exited, status=0/SUCCESS)

 1月 22 23:32:09 black-vps001 systemd[1]: Starting Network Manager Wait Online...
 1月 22 23:32:09 black-vps001 systemd[1]: Started Network Manager Wait Online.
</code>
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設定されているデフォルトタイムアウトを 30 秒から 50 秒(VPS では 240 秒)に変更するとエラーを抑制できる。\\
<code>
$ sudo cp -p /usr/lib/systemd/system/NetworkManager-wait-online.service /etc/systemd/system/.
$ sudo vi /etc/systemd/system/NetworkManager-wait-online.service
</code>
<file autoconf /etc/systemd/system/NetworkManager-wait-online.service>
[Unit]
Description=Network Manager Wait Online
Documentation=man:nm-online(1)
Requires=NetworkManager.service
After=NetworkManager.service
Before=network-online.target

[Service]
Type=oneshot
#ExecStart=/usr/bin/nm-online -s -q --timeout=30
ExecStart=/usr/bin/nm-online -s -q --timeout=50
RemainAfterExit=yes

[Install]
WantedBy=network-online.target
</file>
再起動してエラーが発生しないか確認する。\\
<code>
$ sudo reboot
</code>
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<code>
$ systemctl status NetworkManager-wait-online.service
● NetworkManager-wait-online.service - Network Manager Wait Online
   Loaded: loaded (/etc/systemd/system/NetworkManager-wait-online.service; enabled; vendor preset: enabled)
   Active: active (exited) since Wed 2019-01-23 00:00:07 JST; 1min 47s ago
     Docs: man:nm-online(1)
  Process: 455 ExecStart=/usr/bin/nm-online -s -q --timeout=50 (code=exited, status=0/SUCCESS)
 Main PID: 455 (code=exited, status=0/SUCCESS)

 1月 22 23:59:20 black-vps001 systemd[1]: Starting Network Manager Wait Online...
 1月 23 00:00:07 black-vps001 systemd[1]: Started Network Manager Wait Online.
</code>
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===== 参考文献 =====
[[https://www.support.nec.co.jp/View.aspx?id=3150112904|よくあるご質問(サポートFAQ)・詳細: よくあるご質問(サポートFAQ)・検索一覧 | NEC]]\\