前段時間看到brendangregg的 Linux Performance Analysis and Tools PPT裡面提到的nicstat，研究了下是個不錯的東西，分享給大家。

nicstat is to network interfaces as “iostat” is to disks, or “prstat” is to processes.

nicstat原本是Solaris平臺下顯示網絡卡流量的工具，Tim Cook將它移植到linux平臺，官方網站見 這裡。 相比netstat, 他有以下關鍵特性：

• Reports bytes in & out as well as packets.
• Normalizes these values to per-second rates.
• Reports on all interfaces (while iterating)
• Reports Utilization (rough calculation as of now)
• Reports Saturation (also rough)
• Prefixes statistics with the current time

我們來體驗下，首先安裝之，原始碼在 這裡 下， 目前最新的版本是1.92。
解開後，由於這個版本預設是在32位linux下編譯，所以需要改下Makefile.Linux：

$ uname -r
2.6.32-131.21.1.tb477.el6.x86_64
$ diff Makefile.Linux64 Makefile.Linux
17c17
< CFLAGS =      $(COPT) -m32
---
> CFLAGS =      $(COPT)

$ sudo make -f Makefile.Linux install  
sudo install -o root -g root -m 4511 `./nicstat.sh --bin-name` /usr/local/bin/nicstat
sudo install -o bin -g bin -m 555 enicstat /usr/local/bin
sudo install -o bin -g bin -m 444 nicstat.1 /usr/local/share/man/man1/nicstat.1

enicstat就安裝好可以使用了。

使用文件在這裡： man nicstat
由於在linux下需要獲取網絡卡的speed等資訊，需要以特權使用者執行。

$ sudo enicstat -l
Int      Loopback   Mbit/s Duplex State
lo            Yes        -   unkn    up
eth0           No     1000   full    up
bond0          No        0   unkn    up

$ sudo enicstat 
    Time      Int   rKB/s   wKB/s   rPk/s   wPk/s    rAvs    wAvs %Util    Sat
13:04:10       lo   161.1   161.1   489.2   489.2   337.3   337.3  0.00   0.00
13:04:10     eth0   601.9   589.1  1868.1  1894.1   330.0   318.5  0.98   0.00
13:04:10    bond0   601.9   589.1  1868.1  1894.1   330.0   318.5  0.00   0.00

上面很特色的一個選項就是網絡卡的Util（利用率）以及Saturation（This the number of errors/second seen for the interface）在實踐中用途挺大的。

通過strace和原始碼進行簡單的分析：

open(“/proc/net/dev”, O_RDONLY) = 3
open(“/proc/net/snmp”, O_RDONLY) = 5
open(“/proc/net/netstat”, O_RDONLY) = 6
open(“/proc/uptime”, O_RDONLY) = 9

大部分網絡卡相關的統計資訊是從上面3個檔案獲取到的，其中snmp檔案提供了tcp和udp的統計資訊。

預設統計資訊是以KB為單位，-M選項可以更改為以M為單位，演習如下：

$ sudo enicstat -M
    Time      Int   rMbps   wMbps   rPk/s   wPk/s    rAvs    wAvs %Util    Sat
13:14:51       lo    1.26    1.26   489.1   489.1   337.3   337.3  0.00   0.00
13:14:51     eth0    4.70    4.60  1868.0  1894.0   330.0   318.5  0.98   0.00
13:14:51    bond0    4.70    4.60  1868.0  1894.0   330.0   318.5  0.00   0.00

nicstat還提供了tcp連結外聯和內聯的個數，重置，Drops資訊還有包重傳率等資訊，這些資訊對於診斷tcp問題挺有用的。

$ sudo enicstat -t
13:09:40    InKB   OutKB   InSeg  OutSeg Reset  AttF %ReTX InConn OutCon Drops
TCP         0.00    0.00  2123.7  2251.7  1.84  0.79 0.000   7.16   2.95  0.00

最後需要注意的是, 解讀輸出資訊的時候：

NOTES
On Linux, the NoCP, Defer, TCP InKB, and TCP OutKB statistics are always reported as zero.

The way that saturation is reported is a best effort, as there is no standardized naming to capture
all errors related to an interface’s inability to receive or transmit a packet. Monitoring %Util and
packet rates, along with an understanding of the specific NICs may be more useful in judging whether
you are nearing saturation.

祝玩得開心！

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