tcpdrop.bt(8) System Manager's Manual tcpdrop.bt(8)
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 ker-
nel, 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 func-
tion, 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 unre-
lated, as drops can occur on the receive interrupt and be unre-
lated to the PID that was interrupted.
COMM Process name
SADDR Source IP address.
SPORT Source TCP port.
DADDR Destination IP address.
DPORT Destination TCP port.
STATE TCP session state ("ESTABLISHED", etc).
OVERHEAD
This traces the kernel tcp_drop() function, which should be low fre-
quency, 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.bt(8), tcpaccept.bt(8), tcpconnect.bt(8), tcptop(8)
USER COMMANDS 2018-11-24 tcpdrop.bt(8)
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