This is necessary to prevent a race. Udev 197 has a new naming scheme
for network devices, so it will rename (say) eth0 to eno0. This fails
with "error changing net interface name eth0 to eno1: Device or
resource busy" if another process has opened the interface in the
meantime.
During a configuration switch, changed units are stopped in the old
configuration, then started in the new configuration (i.e. after
running the activation script and running "systemctl daemon-reload").
This ensures that services are stopped using the ExecStop/ExecStopPost
commands from the old configuration.
However, for some services it's undesirable to stop them; in
particular dhcpcd, which deconfigures its network interfaces when it
stops. This is dangerous when doing remote upgrades - usually things
go right (especially because the switch script ignores SIGHUP), but
not always (see 9aa69885f04969e5d31dcb8265c327adc908954e). Likewise,
sshd should be kept running for as long as possible to prevent a
lock-out if the switch fails.
So the new option ‘stopIfChanged = false’ causes "systemctl restart"
to be used instead of "systemctl stop" followed by "systemctl start".
This is only proper for services that don't have stop commands. (And
it might not handle dependencies properly in some cases, but I'm not
sure.)
Thus
networking.interfaces = [ { name = "eth0"; ipAddress = "192.168.15.1"; } ];
can now be written as
networking.interfaces.eth0.ipAddress = "192.168.15.1";
The old notation still works though.
So instead of:
boot.systemd.services."foo".serviceConfig =
''
StartLimitInterval=10
CPUShare=500
'';
you can say:
boot.systemd.services."foo".serviceConfig.StartLimitInterval = 10;
boot.systemd.services."foo".serviceConfig.CPUShare = 500;
This way all unit options are available and users can set/override
options in configuration.nix.
Subtle: dhcpcd.service would call resolvconf during shutdown, which in
turn would start invalidate-nscd.service, causing the shutdown to be
cancelled. Instead, give nscd.service a proper reload action, and do
"systemctl reload --no-block nscd.service". The --no-block is
necessary to prevent that command from waiting until a timeout occurs
(bug in systemd?).
interfaces black-listed for dhcpcd via configuration.nix. I use this option to
disable DHCP for "veth*" interfaces, which are created by LXC for use inside of
virtual machines.
svn path=/nixos/trunk/; revision=34018
delete routes and addresses when it quits. This causes those routes
and addresses to stick around forever, since dhcpcd won't delete
them when it runs next (even if it acquires a new lease on the same
interface). This is bad; in particular the stale (default) routes
can break networking.
The downside to removing "persistent" is that you should never ever
do "stop dhcpcd" on a remote machine configured by dhcpcd.
svn path=/nixos/trunk/; revision=33388
yet). It's smaller than dhclient and has more features
(e.g. automatically detects link status changes, supports
openresolv, does IPv4LL, and supports IPv6 Router Advertisements).
svn path=/nixos/trunk/; revision=32413
