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?
My host is CentOS8 x86_64.
Regards, C. L. Martinez
In article 004E8170-E842-4E8B-9623-DB3EA236DE9F@outlook.com, Carlos Lopez clopmz@outlook.com 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?
Just add a line to the tcpdump script to wait for the interface.
Something like this:
until ifconfig -s | grep -q '^bond0' ; do sleep 1 ; done
Cheers Tony
On Wed, 23 Sep 2020 at 04:33, Carlos Lopez clopmz@outlook.com 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-int...
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)
My host is CentOS8 x86_64.
Regards, C. L. Martinez
CentOS mailing list CentOS@centos.org https://lists.centos.org/mailman/listinfo/centos
Perfect!! Many thanks Stephen. Works like a charm.
On 23/09/2020, 15:08, "CentOS on behalf of Stephen John Smoogen" <centos-bounces@centos.org on behalf of smooge@gmail.com> wrote:
On Wed, 23 Sep 2020 at 04:33, Carlos Lopez clopmz@outlook.com 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-int...
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)
> My host is CentOS8 x86_64. > > > Regards, > C. L. Martinez > > _______________________________________________ > CentOS mailing list > CentOS@centos.org > https://lists.centos.org/mailman/listinfo/centos >
-- Stephen J Smoogen. _______________________________________________ CentOS mailing list CentOS@centos.org https://lists.centos.org/mailman/listinfo/centos
On 9/23/20 7:07 AM, Stephen John Smoogen wrote:
On Wed, 23 Sep 2020 at 04:33, Carlos Lopez clopmz@outlook.com 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-int...
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.
On Wed, 23 Sep 2020 at 23:39, Orion Poplawski orion@nwra.com wrote:
On 9/23/20 7:07 AM, Stephen John Smoogen wrote:
On Wed, 23 Sep 2020 at 04:33, Carlos Lopez clopmz@outlook.com 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-int...
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.
Oh good point. I didn't think about that.
This works for Carlos though because he doesn't need an IP address - just the device existing.
It may or may not.. I just realized that the device may need to get recognized by a switch etc which on a bond may take time.
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.
All good points. Thank you for that douse of reality.
-- Orion Poplawski Manager of NWRA Technical Systems 720-772-5637 NWRA, Boulder/CoRA Office FAX: 303-415-9702 3380 Mitchell Lane orion@nwra.com Boulder, CO 80301 https://www.nwra.com/
On Wed, 23 Sep 2020 at 23:39, Orion Poplawski orion@nwra.com wrote:
On 9/23/20 7:07 AM, Stephen John Smoogen wrote:
On Wed, 23 Sep 2020 at 04:33, Carlos Lopez clopmz@outlook.com 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-int...
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.
Oh good point. I didn't think about that.
This works for Carlos though because he doesn't need an IP address - just the device existing.
It may or may not.. I just realized that the device may need to get recognized by a switch etc which on a bond may take time.
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.
All good points. Thank you for that douse of reality.
I'm just wondering, is there a chance to make this work reliable without modifying the source code of systemd?
Simon
On 24/09/2020 13:41, Simon Matter wrote:
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.
All good points. Thank you for that douse of reality.
I'm just wondering, is there a chance to make this work reliable without modifying the source code of systemd?
Simon
Polling? If "some of [them] do not come up for quite a while" it would not be a problem to add another couple of seconds, I guess.
It might be against an "event driven" aproach, but it would work and you can add all sorts of tests to make sure everything is ready for your job (eg. including reachability of remote services, etc.)
Peter
On 24/09/2020 13:41, Simon Matter wrote:
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.
All good points. Thank you for that douse of reality.
I'm just wondering, is there a chance to make this work reliable without modifying the source code of systemd?
Simon
Polling? If "some of [them] do not come up for quite a while" it would not be a problem to add another couple of seconds, I guess.
It might be against an "event driven" aproach, but it would work and you can add all sorts of tests to make sure everything is ready for your job (eg. including reachability of remote services, etc.)
Sounds like a job for shell scripts then - or how do you integrate it with systemd?
I still have a lot of such stuff waiting here for being ported to the new systemd world and I still don't really know how to do it best.
For pretty standard things it's easy to use systemd unit files but as soon as it gets more complicated, bash scripting feels much easier to me than systemd unit scripting :-(
Simon
On 24/09/2020 16:28, Simon Matter wrote:
On 24/09/2020 13:41, Simon Matter wrote:
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.
All good points. Thank you for that douse of reality.
I'm just wondering, is there a chance to make this work reliable without modifying the source code of systemd?
Simon
Polling? If "some of [them] do not come up for quite a while" it would not be a problem to add another couple of seconds, I guess.
It might be against an "event driven" aproach, but it would work and you can add all sorts of tests to make sure everything is ready for your job (eg. including reachability of remote services, etc.)
Sounds like a job for shell scripts then - or how do you integrate it with systemd?
I still have a lot of such stuff waiting here for being ported to the new systemd world and I still don't really know how to do it best.
For pretty standard things it's easy to use systemd unit files but as soon as it gets more complicated, bash scripting feels much easier to me than systemd unit scripting :-(
Exactly: Write a service that is just a script waiting for all the things to come up and to be ready. Then do the real thing. I guess you could use that script as a target to reach and you could then wait for *that* in other services.
-
Carlos Lopez -
centos＠niob.at -
Orion Poplawski -
Simon Matter -
Stephen John Smoogen -
tony＠softins.co.uk