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added configs for clocks, aka clients

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# Downstream Linux PTP Clients
This directory contains the reusable Linux configuration for servers downstream from NEXUS switch.
The intended path is:
```text
RPi5 Grandmaster
│
\/
Linux Boundary Clock
│
\/
Nexus Boundary Clock
│
\/
Linux client NIC PHC
│
phc2sys
│
\/
CLOCK_REALTIME (UTC)
```
Each direct client normally needs only:
1. `ptp` enabled on its physical NEXUS switch port;
2. `ptp4l` to synchronize the NIC PHC from NEXUS; and
3. `phc2sys` to synchronize Linux `CLOCK_REALTIME` from that PHC.
## Files in this directory
| File | Install as | Purpose |
|---|---|---|
| `ptp4l-client.conf` | `/etc/linuxptp/ptp4l-client.conf` | Ordinary-clock/client-only PTP configuration |
| `ptp4l-client.service` | `/etc/systemd/system/ptp4l-client.service` | Runs `ptp4l` on the client NIC |
| `phc2sys-client.service` | `/etc/systemd/system/phc2sys-client.service` | Synchronizes `CLOCK_REALTIME` from the client NIC PHC |
The bundled files currently use `enp4s0` as the client interface. Change that name everywhere if the target server uses another interface.
## 1. Enable PTP on the corresponding Nexus port
On NEXUS:
```text
configure terminal
interface Ethernet1/<clientPort>
ptp
end
copy running-config startup-config
```
Example:
```text
interface Ethernet1/10
ptp
```
Once the client is online, the Nexus port should normally become `Master` in:
```text
show ptp brief
```
## 2. Install LinuxPTP
On the client:
```bash
sudo apt update
sudo apt install linuxptp ethtool
```
## 3. Identify the PTP NIC
Find the interface connected to NEXUS:
```bash
ip -br link
```
The examples below assume:
```text
enp4s0
```
If your interface has a different name, replace `enp4s0` in all three files before installing them.
For example, search the bundled files with:
```bash
grep -Rni 'enp4s0' .
```
## 4. Verify hardware timestamping
```bash
ethtool -T enp4s0
```
The NIC should expose hardware transmit, receive, and raw hardware timestamping plus a PTP Hardware Clock.
You can map it to the PHC device with:
```bash
readlink -f /sys/class/net/enp4s0/device/ptp/ptp*
```
If the NIC does not support hardware timestamping, do not use the bundled `time_stamping hardware` configuration unchanged.
## 5. Disable competing system-clock synchronization
`phc2sys-client.service` will discipline `CLOCK_REALTIME`. Disable services that would compete for the same system clock:
```bash
sudo systemctl disable --now chrony 2>/dev/null || true
sudo systemctl disable --now systemd-timesyncd 2>/dev/null || true
sudo systemctl disable --now ntp 2>/dev/null || true
sudo systemctl disable --now ntpd 2>/dev/null || true
```
## 6. Install the client files
If the interface really is `enp4s0`, install the files directly:
```bash
sudo install -D -m 0644 ptp4l-client.conf /etc/linuxptp/ptp4l-client.conf
sudo install -D -m 0644 ptp4l-client.service /etc/systemd/system/ptp4l-client.service
sudo install -D -m 0644 phc2sys-client.service /etc/systemd/system/phc2sys-client.service
```
If the interface name is different, edit the local copies first and replace `enp4s0` in:
```text
ptp4l-client.conf
ptp4l-client.service
phc2sys-client.service
```
The PTP client config intentionally uses:
```text
domainNumber 0
network_transport UDPv4
delay_mechanism E2E
clientOnly 1
```
`clientOnly 1` prevents a downstream server from ever trying to become the grandmaster.
## 7. Enable the services
```bash
sudo systemctl daemon-reload
sudo systemctl enable --now ptp4l-client.service
sudo systemctl enable --now phc2sys-client.service
```
The data flow is:
```text
ptp4l: NEXUS -> NIC PHC
phc2sys: NIC PHC -> CLOCK_REALTIME
```
The bundled `phc2sys` service uses:
```bash
phc2sys -s enp4s0 -c CLOCK_REALTIME -w -m
```
`-w` waits for `ptp4l` and obtains the PTP/UTC offset from it, so the client does not need a hard-coded `-37` offset.
## 8. Verification
Check service state:
```bash
systemctl status ptp4l-client
systemctl status phc2sys-client
```
Follow the logs:
```bash
journalctl -fu ptp4l-client
journalctl -fu phc2sys-client
```
`ptp4l` should progress into the synchronized client/slave state and its master offsets should settle near zero.
Query PTP datasets:
```bash
sudo pmc -u -b 0 'GET PORT_DATA_SET'
sudo pmc -u -b 0 'GET CURRENT_DATA_SET'
sudo pmc -u -b 0 'GET PARENT_DATA_SET'
sudo pmc -u -b 0 'GET TIME_STATUS_NP'
```
For a client directly downstream from NEXUS, expect approximately:
```text
portState CLIENT/SLAVE
stepsRemoved 3
grandmasterIdentity <same RPi5 grandmaster identity>
```
In the current topology the RPi5 grandmaster identity observed on NEXUS is:
```text
88a29efffe826ce6
```
If the RPi5 NIC or grandmaster identity changes later, use the currently advertised identity instead of treating that value as permanent.
Also verify the Nexus side:
```text
show ptp brief
```
The client-facing Nexus port should normally be `Master`.
## 9. Quick deployment checklist for another server
```text
NEXUS:
interface Ethernet1/X
ptp
Linux server:
1. install linuxptp + ethtool
2. verify `ethtool -T <NIC>`
3. replace `enp4s0` in the three bundled files if needed
4. install the config and two systemd units
5. disable chrony/timesyncd/ntpd if they discipline CLOCK_REALTIME
6. enable ptp4l-client and phc2sys-client
7. verify logs + pmc output
```
## 10. Troubleshooting
If `ptp4l` stays in LISTENING:
```bash
sudo tcpdump -ni enp4s0 'udp port 319 or udp port 320'
journalctl -u ptp4l-client -n 100 --no-pager
```
Then check NEXUS:
```text
show ptp brief
show ptp packet
```
If the NIC PHC synchronizes but Linux system time does not, inspect:
```bash
journalctl -u phc2sys-client -n 100 --no-pager
systemctl status chrony systemd-timesyncd ntp ntpd
```
Only one service should be responsible for disciplining `CLOCK_REALTIME` on the client.

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# /etc/systemd/system/phc2sys-client.service
[Unit]
Description=Synchronize Linux system clock from PTP PHC
After=ptp4l-client.service
Requires=ptp4l-client.service
[Service]
Type=simple
ExecStart=/usr/sbin/phc2sys \
-s enp4s0 \
-c CLOCK_REALTIME \
-w \
-m
Restart=always
RestartSec=3
[Install]
WantedBy=multi-user.target

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CLIENTS/ptp4l-client.conf Normal file
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# /etc/linuxptp/ptp4l-client.conf
[global]
# Use NIC hardware timestamping
time_stamping hardware
# Match the rest of your PTP domain
domainNumber 0
network_transport UDPv4
delay_mechanism E2E
# This machine must never try to become GM
clientOnly 1
# Useful logging while setting it up
summary_interval 1
[enp4s0]

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CLIENTS/ptp4l-client.service Normal file
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# /etc/systemd/system/ptp4l-client.service
[Unit]
Description=PTP client on enp4s0
After=network-online.target
Wants=network-online.target
[Service]
Type=simple
ExecStart=/usr/sbin/ptp4l \
-i enp4s0 \
-f /etc/linuxptp/ptp4l-client.conf \
-m
Restart=always
RestartSec=3
[Install]
WantedBy=multi-user.target