PTP是一种比NTP精度更高的基于网络的高精度时间同步协议，虽然工作在传输层，但要求网口具有额外的时钟电路，下面介绍一下判断网口是否支持PTP同步的方法。

首先安装ethtool工具，在Debian/Ubuntu下安装命令为：

sudo apt install ethtool

然后使用ifconfig查看需要查询的网口硬件的名称，如eth0、enp4s0这种，然后使用ethtool查看网口对ptp的支持，以我台式机上的PCIe千兆网卡enp4s0为例：

ethtool -T enp4s0

输出结果为：

Time stamping parameters for enp4s0:
 Capabilities:
     software-transmit     (SOF_TIMESTAMPING_TX_SOFTWARE)
     software-receive      (SOF_TIMESTAMPING_RX_SOFTWARE)
     software-system-clock (SOF_TIMESTAMPING_SOFTWARE)
 PTP Hardware Clock: none
 Hardware Transmit Timestamp Modes: none
 Hardware Receive Filter Modes: none

可以看到这里返回PTP Hardware Clock为none，但包括software-transmit、software-receive、software-system-clock，说明这个PCIe网卡不具有PTP的时钟硬件，不支持PTP的硬件时间戳，但支持PTP的软件时间戳，而查询我台式机的主板板载网口enp0s31f6的返回信息为：

Time stamping parameters for enp0s31f6:
 Capabilities:
     hardware-transmit     (SOF_TIMESTAMPING_TX_HARDWARE)
     software-transmit     (SOF_TIMESTAMPING_TX_SOFTWARE)
     hardware-receive      (SOF_TIMESTAMPING_RX_HARDWARE)
     software-receive      (SOF_TIMESTAMPING_RX_SOFTWARE)
     software-system-clock (SOF_TIMESTAMPING_SOFTWARE)
     hardware-raw-clock    (SOF_TIMESTAMPING_RAW_HARDWARE)
 PTP Hardware Clock: 0
 Hardware Transmit Timestamp Modes:
     off                   (HWTSTAMP_TX_OFF)
     on                    (HWTSTAMP_TX_ON)
 Hardware Receive Filter Modes:
     none                  (HWTSTAMP_FILTER_NONE)
     all                   (HWTSTAMP_FILTER_ALL)
     ptpv1-l4-sync         (HWTSTAMP_FILTER_PTP_V1_L4_SYNC)
     ptpv1-l4-delay-req    (HWTSTAMP_FILTER_PTP_V1_L4_DELAY_REQ)
     ptpv2-l4-sync         (HWTSTAMP_FILTER_PTP_V2_L4_SYNC)
     ptpv2-l4-delay-req    (HWTSTAMP_FILTER_PTP_V2_L4_DELAY_REQ)
     ptpv2-l2-sync         (HWTSTAMP_FILTER_PTP_V2_L2_SYNC)
     ptpv2-l2-delay-req    (HWTSTAMP_FILTER_PTP_V2_L2_DELAY_REQ)
     ptpv2-event           (HWTSTAMP_FILTER_PTP_V2_EVENT)
     ptpv2-sync            (HWTSTAMP_FILTER_PTP_V2_SYNC)
     ptpv2-delay-req       (HWTSTAMP_FILTER_PTP_V2_DELAY_REQ)

这里PTP Hardware Clock后面是0，且包括software-transmit、software-receive、software-system-clock和hardware-transmit、hardware-receive、hardware-raw-clock，说明存在PTP硬件时钟，既支持PTP的软件时间戳也支持PTP硬件时间戳。