NAME

       tcpdrop.bt - Trace kernel-based TCP packet drops with details. Uses Linux bpftrace/eBPF

SYNOPSIS

       tcpdrop.bt

DESCRIPTION

       This  tool  traces  TCP  packets  or  segments  that were dropped by the kernel, and shows
       details from the IP and TCP headers, the socket state, and the kernel stack trace. This is
       useful  for  debugging cases of high kernel drops, which can cause timer-based retransmits
       and performance issues.

       This tool works using dynamic tracing of the tcp_drop() kernel function, which requires  a
       recent kernel version.

       This tool is limited to ipv4, and cannot parse tcpflags as bpftrace currently cannot parse
       socket buffers in the way that bcc can.

       Since this uses BPF, only the root user can use this tool.

REQUIREMENTS

       CONFIG_BPF and bpftrace.

EXAMPLES

       Trace all tcp drops:
              # tcpdrop.bt

       FIELDS

       TIME   Time of the call, in HH:MM:SS format.

       PID    Process ID that was on-CPU during the drop. This may be  unrelated,  as  drops  can
              occur on the receive interrupt and be unrelated to the PID that was interrupted.

       COMM   Process name

       SADDR  Source IP address.

       SPORT  Source TCP port.

       DADDR  Destination IP address.

       DPORT  Destionation TCP port.

       STATE  TCP session state ("ESTABLISHED", etc).

OVERHEAD

       This  traces  the kernel tcp_drop() function, which should be low frequency, and therefore
       the overhead of this tool should be negligible.

       As always, test and understand this tools overhead for  your  types  of  workloads  before
       production use.

SOURCE

       This is from bpftrace

              https://github.com/iovisor/bpftrace

       Also  look  in  the  bpftrace  distribution  for a companion _examples.txt file containing
       example usage, output, and commentary for this tool.

       This is a bpftrace version of the bcc tool of the same name. The bcc tool may provide more
       options and customizations.

              https://github.com/iovisor/bcc

OS

       Linux

STABILITY

       Unstable - in development.

AUTHOR

       Brendan Gregg, adapted for bpftrace by Dale Hamel

SEE ALSO

       tcplife(8), tcpaccept(8), tcpconnect(8), tcptop(8)