ss命令的详细输出

Question

我想知道 ss 命令输出中某些项目的含义。例如：

# sudo   ss -iepn '( dport = :3443 )'

Netid      State      Recv-Q      Send-Q             Local Address:Port              Peer Address:Port      
tcp        ESTAB      0           0                  192.168.43.39:45486              190.0.2.1:443       users:(("rocketchat-desk",pid=28697,fd=80)) timer:(keepalive,11sec,0) uid:1000 ino:210510085 sk:16f1 <->
         ts sack cubic wscale:7,7 rto:573 rtt:126.827/104.434 ato:40 mss:1388 pmtu:1500 rcvmss:1388 advmss:1448 cwnd:10 bytes_sent:12904 bytes_retrans:385 bytes_acked:12520 bytes_received:13322 segs_out:433 segs_in:444 data_segs_out:215 data_segs_in:253 send 875.5Kbps lastsnd:18722 lastrcv:18723 lastack:18662 pacing_rate 1.8Mbps delivery_rate 298.1Kbps delivered:216 busy:16182ms retrans:0/10 dsack_dups:10 rcv_rtt:305 rcv_space:14480 rcv_ssthresh:6
CLOSE-WAIT      1           0                [2800:810:54a:7f0::1000]:37844                                     [2800:3f0:4002:803::200a]:443                    users:(("plasma-browser-",pid=16020,fd=175)) uid:1000 ino:90761 sk:1d -->
         ts sack cubic wscale:8,7 rto:222 rtt:21.504/5.045 ato:40 mss:1348 pmtu:1500 rcvmss:1208 advmss:1428 cwnd:10 bytes_sent:1470 bytes_acked:1471 bytes_received:11214 segs_out:20 segs_in:20 data_segs_out:8 data_segs_in:13 send 5014881bps lastsnd:96094169 lastrcv:96137280 lastack:96094142 pacing_rate 10029464bps delivery_rate 1363968bps delivered:9 app_limited busy:91ms rcv_space:14280 rcv_ssthresh:64108 minrtt:17.458

主要是ss手册页中缺少的项目，我做了一些猜测，如果我错了，请纠正我：

• rcvmss：我想知道是彩信接收
• 广告：？
• app_limited: ?
• 忙碌的： ？
• 转发：？
• dsack_dups：重复的段？
• minrtt：在套接字中实现的最小 RTT？

Answer 1

其中一些字段的含义可以从ss和 Linux 内核的源代码中推断出来 。您看到的信息由 中的tcp_show_info() 函数打印iproute2/misc/ss.c。

广告：

在ss.c：

s.advmss     = info->tcpi_advmss;
(...)
    if (s->advmss)
        out(" advmss:%d", s->advmss);

在linux/include/linux/tcp.h：

u16 advmss;     /* Advertised MSS           */

app_limited：

在ss.c：

s.app_limited = info->tcpi_delivery_rate_app_limited;
(..)
if (s->app_limited)
   out(" app_limited");

linux/include/uapi/linux/tcp.h在 Linux 中没有记录那个：

struct tcp_info {
(...)
    __u8    tcpi_delivery_rate_app_limited:1;

但令人惊讶的是，我们可以在引入它的提交中找到一些信息：

commit eb8329e0a04db0061f714f033b4454326ba147f4
Author: Yuchung Cheng <ycheng@google.com>
Date:   Mon Sep 19 23:39:16 2016 -0400

    tcp: export data delivery rate

    This commit export two new fields in struct tcp_info:

      tcpi_delivery_rate: The most recent goodput, as measured by
        tcp_rate_gen(). If the socket is limited by the sending
        application (e.g., no data to send), it reports the highest
        measurement instead of the most recent. The unit is bytes per
        second (like other rate fields in tcp_info).

      tcpi_delivery_rate_app_limited: A boolean indicating if the goodput
        was measured when the socket's throughput was limited by the
        sending application.

    This delivery rate information can be useful for applications that
    want to know the current throughput the TCP connection is seeing,
    e.g. adaptive bitrate video streaming. It can also be very useful for
    debugging or troubleshooting.

快速git blame的ss.c确认app_limited是后添加tcpi_delivery_rate_app_limited加入内核。

忙：

在ss.c：

s.busy_time = info->tcpi_busy_time;
(..)
    if (s->busy_time) {
        out(" busy:%llums", s->busy_time / 1000);

而在include/uapi/linux/tcp.hLinux中，它说：

struct tcp_info {
(...)
    __u64   tcpi_busy_time;      /* Time (usec) busy sending data */

转发：

在ss.c：

s.retrans    = info->tcpi_retrans;
s.retrans_total  = info->tcpi_total_retrans;
(...)
    if (s->retrans || s->retrans_total)
        out(" retrans:%u/%u", s->retrans, s->retrans_total);

tcpi_total_retrans中没有描述linux/include/uapi/linux/tcp.h：

struct tcp_info {
(...)
    __u32   tcpi_total_retrans;

但它用于tcp_get_info()：

void tcp_get_info(struct sock *sk, struct tcp_info *info)
{
    const struct tcp_sock *tp = tcp_sk(sk); /* iff sk_type == SOCK_STREAM */
(...)
    info->tcpi_total_retrans = tp->total_retrans;

并在linux/include/linux/tcp.h其中说：

struct tcp_sock {
(...)
    u32 total_retrans;  /* Total retransmits for entire connection */

tcpi_retrans也没有描述但tcp_get_info() 再次阅读我们看到：

info->tcpi_retrans = tp->retrans_out;

并在linux/include/linux/tcp.h：

struct tcp_sock {
(...)
    u32 retrans_out;    /* Retransmitted packets out        */

dsack_dups：

在ss.c：

s.dsack_dups = info->tcpi_dsack_dups;
(...)
    if (s->dsack_dups)
        out(" dsack_dups:%u", s->dsack_dups);

在include/uapi/linux/tcp.hLinux 中：

struct tcp_info {
(...)
__u32   tcpi_dsack_dups;     /* RFC4898 tcpEStatsStackDSACKDups */

在https://www.ietf.org/rfc/rfc4898.txt 中：

D-SACK 块报告给本地主机的重复段数。