Arch Linux

Step to reproduce:
# systemctl start nsd.service
# systemctl status nsd.service
nsd.service - NSD Name Server Daemon
Loaded: loaded (/usr/lib/systemd/system/nsd.service; disabled)
Active: active (running) since ven. 2014-01-03 00:15:40 CET; 1s ago
Main PID: 12315 (nsd)
CGroup: /system.slice/nsd.service
├─12315 /usr/bin/nsd -c /etc/nsd/nsd.conf
├─12316 /usr/bin/nsd -c /etc/nsd/nsd.conf
└─12321 /usr/bin/nsd -c /etc/nsd/nsd.conf
# systemctl stop nsd.service
# systemctl start nsd.service
# systemctl status nsd.service
nsd.service - NSD Name Server Daemon
Loaded: loaded (/usr/lib/systemd/system/nsd.service; disabled)
Active: failed (Result: exit-code) since ven. 2014-01-03 00:15:56 CET; 1min 43s ago
Process: 12350 ExecStop=/bin/kill -TERM $MAINPID (code=exited, status=1/FAILURE)
Process: 12348 ExecStart=/usr/bin/nsd -c /etc/nsd/nsd.conf (code=exited, status=0/SUCCESS)
Main PID: 12348 (code=exited, status=0/SUCCESS)


journal output:
janv. 03 00:15:40 sheldon.seblu.net systemd[1]: Starting NSD Name Server Daemon...
janv. 03 00:15:40 sheldon.seblu.net systemd[1]: Started NSD Name Server Daemon.
janv. 03 00:15:40 sheldon.seblu.net nsd[12316]: nsd started (NSD 4.0.0), pid 12315
janv. 03 00:15:50 sheldon.seblu.net systemd[1]: Stopping NSD Name Server Daemon...
janv. 03 00:15:50 sheldon.seblu.net systemd[1]: Stopped NSD Name Server Daemon.
janv. 03 00:15:56 sheldon.seblu.net systemd[1]: Starting NSD Name Server Daemon...
janv. 03 00:15:56 sheldon.seblu.net systemd[1]: Started NSD Name Server Daemon.
janv. 03 00:15:56 sheldon.seblu.net kill[12350]: Usage:
janv. 03 00:15:56 sheldon.seblu.net kill[12350]: kill [options] <pid|name> [...]
janv. 03 00:15:56 sheldon.seblu.net kill[12350]: Options:
janv. 03 00:15:56 sheldon.seblu.net kill[12350]: -a, --all do not restrict the name-to-pid conversion to p
janv. 03 00:15:56 sheldon.seblu.net kill[12350]: with the same uid as the present process
janv. 03 00:15:56 sheldon.seblu.net kill[12350]: -s, --signal <sig> send specified signal
janv. 03 00:15:56 sheldon.seblu.net kill[12350]: -q, --queue <sig> use sigqueue(2) rather than kill(2)
janv. 03 00:15:56 sheldon.seblu.net kill[12350]: -p, --pid print pids without signaling them
janv. 03 00:15:56 sheldon.seblu.net kill[12350]: -l, --list [=<signal>] list signal names, or convert one to a name
janv. 03 00:15:56 sheldon.seblu.net kill[12350]: -L, --table list signal names and numbers
janv. 03 00:15:56 sheldon.seblu.net kill[12350]: -h, --help display this help and exit
janv. 03 00:15:56 sheldon.seblu.net kill[12350]: -V, --version output version information and exit
janv. 03 00:15:56 sheldon.seblu.net kill[12350]: For more details see kill(1).
janv. 03 00:15:56 sheldon.seblu.net systemd[1]: nsd.service: control process exited, code=exited status=1
janv. 03 00:15:56 sheldon.seblu.net nsd[12352]: nsd started (NSD 4.0.0), pid 12349
janv. 03 00:15:56 sheldon.seblu.net nsd[12352]: signal received, shutting down...
janv. 03 00:15:56 sheldon.seblu.net systemd[1]: Unit nsd.service entered failed state.


Adding Type=forking, seems to fix this behavior. I guess it's linked to the PIDFile option with Type=simple.