On 9/23/20 7:07 AM, Stephen John Smoogen wrote:
On Wed, 23 Sep 2020 at 04:33, Carlos Lopez <clopmz@xxxxxxxxxxx> wrote:
Hi all,
With SystemD, how can I make certain service dependent on certain network
interfaces being up?
For example, I have an 802.1ad bond interface I need to wait on for being
up (this interface has no ip address assigned, it is used to capture
networks packets with a tcpdump’s script). Every time this service fails
because bond interface is not up.
I have configured the service as:
[Unit]
Description=tcpdump capture script
After=network.target
Wants=network-online.target
But it doesn’t work …. Any tip or trick?
So the network just calls the scripts and exits so they can take a while to
get working. I think this website covers what you want to do
https://unix.stackexchange.com/questions/257888/systemd-wait-for-network-interface-to-be-up-before-running-service
systemctl list-units --no-pager | grep subsystem-net
Then look for the device which matches the one you are listening to. Change
the After=network.target to
BindsTo=sys-devices-virtual-net-<device>.device
After=sys-devices-virtual-net-<device>.device
where <device> is the interface you found (aka eth2, br9, bond0 etc)
Hmm, there seems to be several layers here.
I think sys-devices-<device>.device is "started" when <device> appears
in the kernel:
Sep 23 19:37:25 kernel: virtio_net virtio0 ens3: renamed from eth0
# systemctl status sys-subsystem-net-devices-ens3.device
● sys-subsystem-net-devices-ens3.device - Virtio network device
Loaded: loaded
Active: active (plugged) since Wed 2020-09-23 19:37:25 MDT
This is not what most people would consider "up" - i.e. have an IP
address. ens3 doesn't get it's IP address until much later.
This works for Carlos though because he doesn't need an IP address -
just the device existing.
I have no idea how it worked for the stackexchange poster. Apparently
because "lan0" is a virtual device as well
("sys-devices-virtual-net-lan0") that they need, not a more "physical"
device like "net-devices-ens3", and it gets an IP address at the same
time as creation.
I've been dealing with issues like this for a while - systems with
multiple interfaces, some of which do not come up for quite a while, and
I need to wait for all to be up before running certain tasks. Still
haven't found anything very satisfactory.
--
Orion Poplawski
Manager of NWRA Technical Systems 720-772-5637
NWRA, Boulder/CoRA Office FAX: 303-415-9702
3380 Mitchell Lane orion@xxxxxxxx
Boulder, CO 80301 https://www.nwra.com/
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