Steps to reproduce:
1. Install Ubuntu 16.04 LTS
2. Install LTSP server (dnsmasq as proxy DHCP and tftp; NBD, SSH)
3. Reboot.
4. Boot system
Expected results:
* system boots to online
Actual results:
* system boots offline; it's a security vulnerability as denial of service
Interesting messages from syslog:
Oct 19 15:25:56 server systemd[1]: network-online.target: Found ordering cycle on network-online.target/stop
Oct 19 15:25:56 server systemd[1]: network-online.target: Found dependency on network.target/stop
Oct 19 15:25:56 server systemd[1]: network-online.target: Found dependency on NetworkManager.service/stop
Oct 19 15:25:56 server systemd[1]: network-online.target: Found dependency on basic.target/stop
Oct 19 15:25:56 server systemd[1]: network-online.target: Found dependency on paths.target/stop
Oct 19 15:25:56 server systemd[1]: network-online.target: Found dependency on cups.path/stop
Oct 19 15:25:56 server systemd[1]: network-online.target: Found dependency on sysinit.target/stop
Oct 19 15:25:56 server systemd[1]: network-online.target: Found dependency on nbd-client.service/stop
Oct 19 15:25:56 server systemd[1]: network-online.target: Found dependency on network-online.target/stop
Oct 19 15:25:56 server systemd[1]: network-online.target: Breaking ordering cycle by deleting job network.target/stop
Oct 19 15:25:56 server systemd[1]: network.target: Job network.target/stop deleted to break ordering cycle starting with network-online.target/stop
ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: systemd 229-4ubuntu19
ProcVersionSignature: Ubuntu 4.4.0-93.116-generic 4.4.79
Uname: Linux 4.4.0-93-generic i686
ApportVersion: 2.20.1-0ubuntu2.10
Architecture: i386
CurrentDesktop: MATE
Date: Thu Oct 26 13:50:49 2017
InstallationDate: Installed on 2016-04-21 (552 days ago)
InstallationMedia: Ubuntu 16.04 LTS "Xenial Xerus" - Release i386 (20160420.1)
MachineType: Gigabyte Technology Co., Ltd. To be filled by O.E.M.
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-4.4.0-93-generic root=UUID=26069a01-c072-4021-83c5-f6df23dc51d5 ro net.ifnames=0 biosdevname=0 quiet splash vt.handoff=7
SourcePackage: systemd
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 01/09/2014
dmi.bios.vendor: American Megatrends Inc.
dmi.bios.version: FD
dmi.board.asset.tag: To be filled by O.E.M.
dmi.board.name: F2A55M-DS2
dmi.board.vendor: Gigabyte Technology Co., Ltd.
dmi.board.version: x.x
dmi.chassis.asset.tag: To Be Filled By O.E.M.
dmi.chassis.type: 3
dmi.chassis.vendor: Gigabyte Technology Co., Ltd.
dmi.chassis.version: To Be Filled By O.E.M.
dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvrFD:bd01/09/2014:svnGigabyteTechnologyCo.,Ltd.:pnTobefilledbyO.E.M.:pvrTobefilledbyO.E.M.:rvnGigabyteTechnologyCo.,Ltd.:rnF2A55M-DS2:rvrx.x:cvnGigabyteTechnologyCo.,Ltd.:ct3:cvrToBeFilledByO.E.M.:
dmi.product.name: To be filled by O.E.M.
dmi.product.version: To be filled by O.E.M.
dmi.sys.vendor: Gigabyte Technology Co., Ltd.
Thanks for taking the time to report this bug and helping to make Ubuntu better. We appreciate the difficulties you are facing, but this appears to be a "regular" (non-security) bug. I have unmarked it as a security issue since this bug does not show evidence of allowing attackers to cross privilege boundaries nor directly cause loss of data/privacy. Please feel free to report any other bugs you may find.