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.

DADDR

Remote IP address.

LPORT

Local port.

DPORT

Destination 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

SEE ALSO¶

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