Em vez de adivinhar, você pode ver os logs do NetworkManager via journalctl
e ver por que ele está entrando nesse estado de erro:
$ journalctl -u NetworkManager
Jul 31 17:41:04 centos7 dhclient[794]: bound to 10.0.2.15 -- renewal in 42481 seconds.
Aug 01 05:29:05 centos7 dhclient[794]: DHCPREQUEST on eth0 to 10.0.2.2 port 67 (xid=0x4c2d7b4e)
Aug 01 05:29:05 centos7 dhclient[794]: DHCPACK from 10.0.2.2 (xid=0x4c2d7b4e)
Aug 01 05:29:05 centos7 NetworkManager[699]: <info> [1533115745.8815] dhcp4 (eth0): address 10.0.2.15
Aug 01 05:29:05 centos7 NetworkManager[699]: <info> [1533115745.8815] dhcp4 (eth0): plen 24 (255.255.255.0)
Aug 01 05:29:05 centos7 NetworkManager[699]: <info> [1533115745.8815] dhcp4 (eth0): gateway 10.0.2.2
Aug 01 05:29:05 centos7 NetworkManager[699]: <info> [1533115745.8816] dhcp4 (eth0): lease time 86400
Aug 01 05:29:05 centos7 NetworkManager[699]: <info> [1533115745.8816] dhcp4 (eth0): nameserver '10.0.2.3'
Aug 01 05:29:05 centos7 NetworkManager[699]: <info> [1533115745.8816] dhcp4 (eth0): state changed bound -> bound
Aug 01 05:29:05 centos7 dhclient[794]: bound to 10.0.2.15 -- renewal in 35729 seconds.
Se você precisar de detalhes adicionais de registro, poderá aumentar o nível de logon do NetworkManager:
nível atual
$ nmcli general logging
LEVEL DOMAINS
INFO PLATFORM,RFKILL,ETHER,WIFI,BT,MB,DHCP4,DHCP6,PPP,IP4,IP6,AUTOIP4,DNS,VPN,SHARING,SUPPLICANT,AGENTS,SETTINGS,SUSPEND,CORE,DEVICE,OLPC,INFINIBAND,FIREWALL,ADSL,BOND,VLAN,BRIDGE,TEAM,CONCHECK,DCB,DISPATCH,AUDIT,SYSTEMD,PROXY
As etapas acima mostram que o nível de log está definido como INFO
e que DOMAINS está definido como PLATFORM....
. Para aumentar o nível de log:
$ nmcli general logging level DEBUG
Vendo que foi aumentado:
$ journalctl -u NetworkManager | tail -1
Aug 01 06:32:26 centos7 NetworkManager[699]: <info> [1533119546.8161] manager: logging: level 'DEBUG' domains 'PLATFORM,RFKILL,ETHER,WIFI,BT,MB,DHCP4,DHCP6,PPP,IP4,IP6,AUTOIP4,DNS,VPN,SHARING,SUPPLICANT,AGENTS,SETTINGS,SUSPEND,CORE,DEVICE,OLPC,INFINIBAND,FIREWALL,ADSL,BOND,VLAN,BRIDGE,TEAM,CONCHECK,DCB,DISPATCH,AUDIT,SYSTEMD,PROXY'
Referências