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ss option explains

ss output may have different format for difference protocol type, this document explains the format base on the TCP protocol

-m option

Show memory information. Format:

skmem:(r<rmem_alloc>,rb<rcv_buf>,t<wmem_alloc>,tb<snd_buf>,f<fwd_alloc>,w<wmem_queued>,o<opt_mem>,bl<back_log>)
  • <rmem_alloc>
    the memory allocated for receiving package
  • <rcv_buf>
    the total memory can be allocated for receiving package
  • <wmem_alloc>
    the memory used for sending package (which has been sent to layer 3).
  • <snd_buf>
    the total memory can be allocated for sending package
  • <fwd_alloc>
    the memory allocated by the socket as cache, but not used for receiving/sending pacakge yet. If need memory to send/receive package, the memory in this cache will be used before allocate additional memory.
  • <wmem_queued>
    The memory allocated for sending package (which has not been sent to layer 3).
  • <opt_mem>
    The memory used for storing socket option, e.g., the key for TCP MD5 signature.
  • <back_log>
    The memory used for the sk backlog queue. On a process context, if the process is receving package, and a new package is received, it will be put into the sk backlog queue, so it can be received by the process immediately.

-o option

Show timer information. Format:

timer:(<timer_name>,<expire_time>,<retrans>)
  • <timer_name>
    the name of the timer, there are five kinds of timer names:
    • on: means one of these timers: tcp retrans timer, tcp early retrans timer and tail loss probe timer
    • keepalive: tcp keep alive timer
    • timewait: timewait stage timer
    • persist: zero window probe timer
    • unknown: none of the above timers
  • <expire_time>
    how long time the timer will expire
  • retrans
    how many times the retran occurs

-e option

Show additional socket information. Format:

uid:<uid_number> ino:<inode_number> sk:<cookie>
  • <uid_number>
    the user id the socket belongs to
  • <inode_number>
    the socket's inode number in VFS
  • <cookie>
    an uuid of the socket

-i option

show tcp internal information

  • ts
    show string "ts" if the timestamp option is set
  • sack
    show string "sack" if the sack option is set
  • ecn
    show string "ecn" if the explicit congestion notification option is set
  • ecnseen
    show string "ecnseen" if the saw ecn flag is found in received packages
  • fastopen
    show string "fastopen" if the fastopen option is set
  • cong_alg
    the congestion algorithm name, the default congestion algorithm is "cubic"
  • wscale:<snd_wscale>:<rcv_wscale>
    if window scale option is used, this field shows the send scale factory and receive scale factory
  • rto:<icsk_rto>
    tcp retransmission timeout value, the unit is millisecond
  • backoff:<icsk_backoff>
    used for exponential backoff retransmission, the actual retransmission timeout vaule is icsk_rto << icsk_backoff
  • rtt:<rtt>/<rttvar>
    rtt is the average round trip time, rttvar is the mean deviation of rtt, their units are millisecond
  • ato:<ato>
    ack timeout, unit is millisecond, used for delay ack mode
  • mss:<mss>
    max segment size
  • cwnd:<cwnd>
    congestion window size
  • ssthresh:<ssthresh>
    tcp congestion window slow start threshold
  • bytes_acked:<bytes_acked>
    bytes acked
  • bytes_received:<bytes_received>
    bytes received
  • segs_out:<segs_out>
    segments sent out
  • segs_in:<segs_in>
    segments received
  • send <send_bps>bps
    egress bps
  • lastsnd:<lastsnd>
    how long time since the last package sent, the unit is millisecond
  • lastrcv:<lastrcv>
    how long time since the last package received, the unit is millisecond
  • lastack:<lastack>
    how long time since the last ack received, the unit is millisecond
  • pacing_rate <pacing_rate>bps/<max_pacing_rate>bps
    the pacing rate and max pacing rate
  • rcv_space:<rcv_space>
    a helper variable for TCP internal auto tunning socket receive buffer