NAME¶

tcpaccept - Trace TCP passive connections (accept()). Uses Linux eBPF/bcc.

SYNOPSIS¶

tcpaccept [-h] [-T] [-t] [-p PID] [-P PORTS] [-4 | -6] [--cgroupmap MAPPATH] [--mntnsmap MAPPATH]

DESCRIPTION¶

This tool traces passive TCP connections (eg, via an accept() syscall; connect() are active connections). This can be useful for general troubleshooting to see what new connections the local server is accepting.

This uses dynamic tracing of the kernel inet_csk_accept() socket function (from tcp_prot.accept), and will need to be modified to match kernel changes.

This tool only traces successful TCP accept()s. Connection attempts to closed ports will not be shown (those can be traced via other functions).

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

REQUIREMENTS¶

CONFIG_BPF and bcc.

OPTIONS¶

-h

Print usage message.

-T

Include a time column on output (HH:MM:SS).

-t

Include a timestamp column.

-p PID

Trace this process ID only (filtered in-kernel).

-P PORTS

Comma-separated list of local ports to trace (filtered in-kernel).

-4

Trace IPv4 family only.

-6

Trace IPv6 family only.

--cgroupmap MAPPATH

Trace cgroups in this BPF map only (filtered in-kernel).

--mntnsmap MAPPATH

Trace mount namespaces in this BPF map only (filtered in-kernel).

EXAMPLES¶

Trace all passive TCP connections (accept()s):

# tcpaccept

Trace all TCP accepts, and include timestamps:

# tcpaccept -t

Trace connections to local ports 80 and 81 only:

# tcpaccept -P 80,81

Trace PID 181 only:

# tcpaccept -p 181

Trace IPv4 family only:

# tcpaccept -4

Trace IPv6 family only:

# tcpaccept -6

Trace a set of cgroups only (see special_filtering.md from bcc sources for more details):

# tcpaccept --cgroupmap /sys/fs/bpf/test01

FIELDS¶

TIME

Time of the event, in HH:MM:SS format.

TIME(s)

Time of the event, in seconds.

PID

Process ID

COMM

Process name

IP

IP address family (4 or 6)

RADDR

Remote IP address.

RPORT

Remote port

LADDR

Local IP address.

LPORT

Local port

OVERHEAD¶

This traces the kernel inet_csk_accept function and prints output for each event. The rate of this depends on your server application. If it is a web or proxy server accepting many tens of thousands of connections per second, then the overhead of this tool may be measurable (although, still a lot better than tracing every packet). If it is less than a thousand a second, then the overhead is expected to be negligible. Test and understand this overhead before 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

AUTHOR¶

Brendan Gregg

SEE ALSO¶

tcptracer(8), tcpconnect(8), funccount(8), tcpdump(8)