NAME

tcpstates - Trace TCP session state changes with durations. Uses Linux eBPF/bcc.

SYNOPSIS

tcpstates [-h] [-T] [-t] [-w] [-s] [-D PORTS] [-L PORTS] [-Y]

DESCRIPTION

This tool traces TCP session state changes while tracing, and prints details including the duration in each state. This can help explain the latency of TCP connections: whether the time is spent in the ESTABLISHED state (data transfer), or initialization state (SYN_SENT), etc.

This tool works using the sock:inet_sock_set_state tracepoint, which was added to Linux 4.16. Linux 4.16 also included extra state transitions so that all TCP transitions could be observed by this tracepoint.

Only TCP state changes are traced, so it is expected that the overhead of this tool is much lower than typical send/receive tracing.

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

REQUIREMENTS

CONFIG_BPF and bcc, and the sock:inet_sock_set_state tracepoint.

OPTIONS

-h: Print usage message.
-s: Comma separated values output (parseable).
-t: Include a timestamp column (seconds).
-T: Include a time column (HH:MM:SS).
-w: Wide column output (fits IPv6 addresses).
-L PORTS: Comma-separated list of local ports to trace (filtered in-kernel).
-D PORTS: Comma-separated list of destination ports to trace (filtered in-kernel).
-Y: Log session state changes to the systemd journal.

EXAMPLES

Trace all TCP sessions, and show all state changes:: # tcpstates
Include a timestamp column, and wide column output:: # tcpstates -tw
Trace connections to local ports 80 and 81 only:: # tcpstates -L 80,81
Trace connections to remote port 80 only:: # tcpstates -D 80

FIELDS

TIME: Time of the change, in HH:MM:SS format.
TIME(s): Time of the change, in seconds.
C-PID: The current on-CPU process ID. This may show the process that owns the TCP session if the state change executes in synchronous process context, else it is likely to show the kernel (asynchronous state change).
C-COMM: The current on-CPU process name. This may show the process that owns the TCP session if the state change executes in synchronous process context, else it is likely to show the kernel (asynchronous state change).
IP: IP address family (4 or 6)
LADDR: Local IP address.
RADDR: Remote IP address.
LPORT: Local port.
RPORT: Remote port.
OLDSTATE: Previous TCP state.
NEWSTATE: New TCP state.
MS: Duration of this state.

OVERHEAD

This traces the kernel TCP set state function, which should be called much less often than send/receive tracing, and therefore have lower overhead. The overhead of the tool is relative to the rate of new TCP sessions: if this is high, over 10,000 per second, then there may be noticeable overhead just to print out 10k lines of formatted output per second.

You can find out the rate of new TCP sessions using "sar -n TCP 1", and adding the active/s and passive/s columns.

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

SOURCE

This is from bcc.

: https://github.com/iovisor/bcc

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

OS

Linux

STABILITY

Unstable - in development.

AUTHOR

Brendan Gregg