https://www.jianshu.com/p/f456e73a0437
ethtool - query or control network driver and hardware settings
with a single argument specifying the device name prints current settings of the specified device.
ethtool eno1
Settings for eno1:
Supported ports: [ ]
Supported link modes: 1000baseT/Full
Supported pause frame use: Symmetric
Supports auto-negotiation: Yes
Supported FEC modes: Not reported
Advertised link modes: 1000baseT/Full
Advertised pause frame use: No
Advertised auto-negotiation: Yes
Advertised FEC modes: Not reported
Speed: Unknown!
Duplex: Unknown! (255)
Port: Other
PHYAD: 0
Transceiver: internal
Auto-negotiation: off
Supports Wake-on: g
Wake-on: g
Current message level: 0x00000007 (7)
drv probe link
Link detected: no
# ethtool ens5f0
Settings for ens5f0:
Supported ports: [ FIBRE ]
Supported link modes: 1000baseKX/Full ##支持的链路模式
10000baseKR/Full
25000baseCR/Full
25000baseKR/Full
25000baseSR/Full
Supported pause frame use: Symmetric ##暂停帧的支持，以太网流量控制
Supports auto-negotiation: Yes ##链路自动协商
Supported FEC modes: None BaseR
Advertised link modes: 1000baseKX/Full
10000baseKR/Full
25000baseCR/Full
25000baseKR/Full
25000baseSR/Full
Advertised pause frame use: Symmetric
Advertised auto-negotiation: Yes ##建议自动协商
Advertised FEC modes: None ##建议的FEC mode
Speed: 10000Mb/s ##速率
Duplex: Full ##双工模式
Port: FIBRE ##port类型，，还会有
PHYAD: 0 ##网卡的物理标识，如果两个device的PHYAD相同，表示在一块物理网卡上
Transceiver: internal ##internal — Use internal transceiver、external — Use external transceiver.
Auto-negotiation: on
Supports Wake-on: d
Wake-on: d ##Wake On LAN是否启用,d:禁用，g:启用
Current message level: 0x00000004 (4)
link
Link detected: yes ##对于link也有一个比较实用的redhat kb:https://access.redhat.com/solutions/46885
Shows the ethtool version number.
# ethtool --version
ethtool version 4.8
Queries the specified Ethernet device for pause parameter information.
[root@localhost ~]# ethtool -a eno1
Pause parameters for eno1:
Autonegotiate: off
RX: off
TX: off
[root@localhost ~]# ethtool --show-pause eno1
Pause parameters for eno1:
Autonegotiate: off
RX: off
TX: off
当以太网卡不能处理对端发送的数据帧时，将发送‘PAUSE’帧到对端，请求暂停发送。
当本端以太网卡可处理更多数据时，或者‘PAUSE’请求的暂停时间超时，对端可继续发送数据。可使用以下的ethtool命令查看网卡的流控设置。
Queries the specified network device for rx/tx ring parameter information.
[root@localhost ~]# ethtool -g eno3
Ring parameters for eno3:
Pre-set maximums:
RX: 4096
RX Mini: 0
RX Jumbo: 0
TX: 4096
Current hardware settings:
RX: 512
RX Mini: 0
RX Jumbo: 0
TX: 512
ringbuffer
The network interface ("NIC") shares a data structure with the operating system kernel software in order to pass network packets between them. Usually there are separate structures for transmit and receive directions, and commonly the data structure employed is a logical ring of buffers. This results in the term "ring buffer" being often used to indicate this interface structure. Usually all the buffers in a ring are of the same size.
The kernel device driver for the NIC, and the NIC firmware or hardware, cooperate in managing the data structure.
ifconfig输出下的drop error 通常跟ringbuffer相关。
ens5f0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
ether 98:03:9b:48:c7:dc txqueuelen 1000 (Ethernet)
RX packets 2815480 bytes 236634030 (225.6 MiB)
RX errors 0 dropped 441 overruns 0 frame 0
TX packets 0 bytes 0 (0.0 B)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
Changes the rx/tx ring parameters of the specified network device.
rx N Changes the number of ring entries for the Rx ring.
rx-mini N Changes the number of ring entries for the Rx Mini ring.
rx-jumbo N Changes the number of ring entries for the Rx Jumbo ring.
tx N Changes the number of ring entries for the Tx ring.
设置ringbuffer的大小
[root@localhost ~]# ethtool -G ens5f0 rx 2048
[root@localhost ~]# ethtool -g ens5f0
Ring parameters for ens5f0:
Pre-set maximums:
RX: 8192
RX Mini: 0
RX Jumbo: 0
TX: 8192
Current hardware settings:
RX: 2048
RX Mini: 0
RX Jumbo: 0
TX: 1024
ethtool -G 命令设置ringbuffer为临时生效
永久生效方法，可参考如下linux kb：https://access.redhat.com/solutions/2127401
Queries the specified network device for associated driver information.
查询网卡的driver以及微码版本
[root@localhost ~]# ethtool -i eno1
driver: i40e
version: 2.8.20-k
firmware-version: 5.10 0x80002c06 1.2890.0
expansion-rom-version:
bus-info: 0000:5b:00.2
supports-statistics: yes
supports-test: yes
supports-eeprom-access: yes
supports-register-dump: yes
supports-priv-flags: yes
--可以查看到网卡的driver信息
--可以查看到网卡的微码版本信息
--可以查看到网卡的总线信息，这个也是比较有用的，bus number结合lspci命令可以如下这样使用：
[root@localhost ~]# lspci -s 5b:00.2 -v
5b:00.2 Ethernet controller: Intel Corporation Ethernet Connection X722 for 1GbE (rev 09)
Subsystem: Lenovo Ethernet Connection X722 for 1GbE
Flags: bus master, fast devsel, latency 0, IRQ 32, NUMA node 0
Memory at 23ffb000000 (64-bit, prefetchable) [size=16M]
Memory at 23fff008000 (64-bit, prefetchable) [size=32K]
Expansion ROM at e3b80000 [disabled] [size=512K]
Capabilities: [40] Power Management version 3
Capabilities: [50] MSI: Enable- Count=1/1 Maskable+ 64bit+
Capabilities: [70] MSI-X: Enable+ Count=129 Masked-
Capabilities: [a0] Express Endpoint, MSI 00
Capabilities: [e0] Vital Product Data
Capabilities: [100] Advanced Error Reporting
Capabilities: [150] Alternative Routing-ID Interpretation (ARI)
Capabilities: [160] Single Root I/O Virtualization (SR-IOV)
Capabilities: [1a0] Transaction Processing Hints
Capabilities: [1b0] Access Control Services
Kernel driver in use: i40e
Kernel modules: i40e
Initiates adapter-specific action intended to enable an operator to easily identify the adapter by sight. Typically this involves blinking one or more LEDs on the specific network port.
小写的P,点亮网卡，用来定位网卡物理位置，命令执行后，ctrl+c 取消执行：
[root@localhost ~]# ethtool -p eno1
^C
Queries the specified network device for permanent hardware address.
大写的p，查看网卡的mac地址、ip ad和ifconfig等命令均可实现这种功能。
[root@localhost ~]# ethtool -P eno1
Permanent address: 08:94:ef:9c:13:ea
[root@localhost ~]# ip ad |grep -i eno1 -A 1
4: eno1: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc mq state DOWN group default qlen 1000
link/ether 08:94:ef:9c:13:ea brd ff:ff:ff:ff:ff:ff
[root@localhost ~]# ifconfig eno1
eno1: flags=4099<UP,BROADCAST,MULTICAST> mtu 1500
ether 08:94:ef:9c:13:ea txqueuelen 1000 (Ethernet)
RX packets 0 bytes 0 (0.0 B)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 0 bytes 0 (0.0 B)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
Restarts auto-negotiation on the specified Ethernet device, if auto-negotiation is enabled.
[root@localhost ~]# ethtool -r eno3
[root@localhost ~]#
看下实际效果，系统会让网卡再重新协商一次链路，可以看到如下日志输出：
localhost kernel: i40e 0000:5b:00.0 eno3: NIC Link is Down
localhost kernel: i40e 0000:5b:00.0 eno3: NIC Link is Up, 10 Gbps Full Duplex, Flow Control: None
localhost NetworkManager[1886]: <info> [1670530932.4519] device (eno3): carrier: link connected
Queries the specified network device for NIC- and driver-specific statistics.
这个命令输出信息会非常多，也是非常有用的：
[root@localhost ~]# ethtool -S eno3|more
NIC statistics:
rx_packets: 2330214 # Trasmitted packets
tx_packets: 63464 #Received packets
rx_bytes: 230354804
tx_bytes: 14182808
rx_errors: 0 #Trasmission errors
tx_errors: 0 #Received errors
rx_dropped: 0
tx_dropped: 0
collisions: 0
rx_length_errors: 0
rx_crc_errors: 0
rx_unicast: 34715
tx_unicast: 48219
rx_multicast: 11552
tx_multicast: 15241
rx_broadcast: 2283947
tx_broadcast: 4
rx_unknown_protocol: 0
tx_linearize: 0
--对于统计信息，一方面理解各个信息代表的含义是重要的，这方面mellanox有一个文档相对比较详细：https://support.mellanox.com/s/article/understanding-mlx5-ethtool-counters
--零一点对于排障比较重要的是，在排障过程中通常需要对计数器进行重置，redhat对此有一篇文档：
https://access.redhat.com/solutions/125793
--实际上ethtool -S 的计数信息对于排查IP层的丢包、物理层的丢包有着比较重要的意义，有一个思路是首先首先要判断丢包是发生在tcp/ip哪个层面，然后从ethtool -S的技术中查看丢包的原因。
--实际上ethtool -S 的计数信息对于排查IP层的丢包、物理层的丢包有着比较重要的意义，有一个思路是首先首先要判断丢包是发生在tcp/ip哪个层面，然后从ethtool -S的技术中查看丢包的原因。
Allows changing some or all settings of the specified network device. All following options only apply if -s was specified.
speed N
Set speed in Mb/s. ethtool with just the device name as an argument will show you the supported device speeds.
duplex half|full
Sets full or half duplex mode.
port tp|aui|bnc|mii
Selects device port.
mdix auto|on|off
Selects MDI-X mode for port. May be used to override the automatic detection feature of most adapters. An argument of auto means automatic detection of MDI status, on
forces MDI-X (crossover) mode, while off means MDI (straight through) mode. The driver should guarantee that this command takes effect immediately, and if necessary
may reset the link to cause the change to take effect.
autoneg on|off
Specifies whether autonegotiation should be enabled. Autonegotiation is enabled by default, but in some network devices may have trouble with it, so you can disable it
if really necessary
Queries the specified network device for its private flags. The names and meanings of private flags (if any) are defined by each network device driver.
--set-priv-flags
Sets the device's private flags as specified.
flag on|off Sets the state of the named private flag.
对网卡设置一些私有的标志，这些选项跟驱动强相关，意味着如果驱动版本低的话，则无法修改这些选项。
通常是在一些特定的场景下才会需要修改这些标志，如下一个案例：
https://access.redhat.com/solutions/4054441
Queries the specified network device for its support of Forward Error Correction.
一种前向错误纠正技术，旨在增强数据传输的可靠性。
Forward error correction (FEC) is an error correction technique to detect and correct a limited number of errors in transmitted data without the need for retransmission.
In this method, the sender sends a redundant error-correcting code along with the data frame. The receiver performs necessary checks based upon the additional redundant bits. If it finds that the data is free from errors, it executes error-correcting code that generates the actual frame. It then removes the redundant bits before passing the message to the upper layers.
通过如下命令进行查询
[root@localhost ~]# which ethtool
/usr/sbin/ethtool
[root@localhost ~]# rpm -qf /usr/sbin/ethtool
ethtool-4.8-10.el7.x86_64