1tcpconnect(8) System Manager's Manual tcpconnect(8)
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6 tcpconnect - Trace TCP active connections (connect()). Uses Linux
7 eBPF/bcc.
8
10 tcpconnect [-h] [-c] [-t] [-p PID] [-P PORT] [-L] [-u UID] [-U]
11 [--cgroupmap MAPPATH] [--mntnsmap MAPPATH] [-d]
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14 This tool traces active TCP connections (eg, via a connect() syscall;
15 accept() are passive connections). This can be useful for general trou‐
16 bleshooting to see what connections are initiated by the local server.
17 All connection attempts are traced, even if they ultimately fail.
19 This works by tracing the kernel tcp_v4_connect() and tcp_v6_connect()
21 functions using dynamic tracing, and will need updating to match any
22 changes to these functions.
23 When provided with the -d or --dns option, this tool will also corre‐
25 late connect calls with the most recent DNS query that matches the IP
26 connected. This feature works by tracing the kernel udp_recvmsg()
27 function to collect DNS responses.
28 Since this uses BPF, only the root user can use this tool.
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32 CONFIG_BPF and bcc.
33 If using the -d or --dns option, you must have the dnslib and ca‐
35 chetools python packages installed. You can install them with pip3 or
36 with apt on Ubuntu 18.04+ using the python3-dnslib and python3-ca‐
37 chetools packages.
38
40 -h Print usage message.
41 -t Include a timestamp column.
43 -c Count connects per src ip and dest ip/port.
45 -p PID Trace this process ID only (filtered in-kernel).
47 -P PORT
49 Comma-separated list of destination ports to trace (filtered in-
50 kernel).
51 -L Include a LPORT column.
53 -U Include a UID column.
55 -u UID Trace this UID only (filtered in-kernel).
57 --cgroupmap MAPPATH
59 Trace cgroups in this BPF map only (filtered in-kernel).
60 --mntnsmap MAPPATH
62 Trace mount namespaces in this BPF map only (filtered in-ker‐
63 nel).
64 -d Shows the most recent DNS query for the IP address in the con‐
66 nect call. This is likely related to the TCP connection details
67 in the other columns, but is not guaranteed. This feature works
68 by tracing the udp_recvmsg kernel function and tracking DNS re‐
69 sponses received by the server. It only supports UDP DNS pack‐
70 ets up to 512 bytes in length. The python code keeps a cache of
71 10k DNS responses in memory for up 24 hours.
72 If the time difference in milliseconds between when the system
74 received a DNS response and when a connect syscall was traced
75 using an IP in that DNS response is greater than 100ms, this
76 tool will report this delta after the query. These deltas
77 should be relatively short for most applications. A long delay
78 between the response and connect could be either anomalous ac‐
79 tivity or indicate a misattribution between the DNS name re‐
80 quested and the IP that the connect syscall is using.
81 The -d option may not be used with the count feature (option -c)
83
85 Trace all active TCP connections:
86 # tcpconnect
87 Trace all TCP connects, and include timestamps:
89 # tcpconnect -t
90 Trace all TCP connects, and include most recent matching DNS query for
92 each connected IP
93 # tcpconnect -d
94 Trace PID 181 only:
96 # tcpconnect -p 181
97 Trace ports 80 and 81 only:
99 # tcpconnect -P 80,81
100 Trace all TCP connects, and include LPORT:
102 # tcpconnect -L
103 Trace all TCP connects, and include UID:
105 # tcpconnect -U
106 Trace UID 1000 only:
108 # tcpconnect -u 1000
109 Count connects per src ip and dest ip/port:
111 # tcpconnect -c
112 Trace a set of cgroups only (see special_filtering.md from bcc sources
114 for more details):
115 # tcpconnect --cgroupmap /sys/fs/bpf/test01
116 Trace a set of mount namespaces only (see special_filtering.md from bcc
118 sources for more details):
119 # tcpconnect --mntnsmap /sys/fs/bpf/mnt_ns_set
120
122 TIME(s)
123 Time of the call, in seconds.
124 UID User ID
126 PID Process ID
128 COMM Process name
130 IP IP address family (4 or 6)
132 SADDR Source IP address.
134 LPORT Source port
136 DADDR Destination IP address.
138 DPORT Destination port
140 CONNECTS
142 Accumulated active connections since start.
143 QUERY Shows the most recent DNS query for the IP address in the con‐
145 nect call. This is likely related to the TCP connection details
146 in the other columns, but is not guaranteed.
147
149 This traces the kernel tcp_v[46]_connect functions and prints output
150 for each event. As the rate of this is generally expected to be low (<
151 1000/s), the overhead is also expected to be negligible. If you have an
152 application that is calling a high rate of connect()s, such as a proxy
153 server, then test and understand this overhead before use.
154 If you are using the -d option to track DNS requests, this tool will
156 trace the udp_recvmsg function and generate an event for any packets
157 from UDP port 53. This event contains up to 512 bytes of the UDP
158 packet payload. Typical applications do not extensively use UDP, so
159 the performance overhead of tracing udp_recvmsg is expected to be neg‐
160 ligible, However, if you have an application that receives many UDP
161 packets, then you should test and understand the overhead of tracing
162 every received UDP message. Furthermore, performance overhead of run‐
163 ning this tool on a DNS server is expected to be higher than average
164 because all DNS response packets will be copied to userspace.
165
167 This is from bcc.
168 https://github.com/iovisor/bcc
170 Also look in the bcc distribution for a companion _examples.txt file
172 containing example usage, output, and commentary for this tool.
173
175 Linux
176
178 Unstable - in development.
179
181 Brendan Gregg
182
184 tcptracer(8), tcpaccept(8), funccount(8), tcpdump(8)
185USER COMMANDS 2020-02-20 tcpconnect(8)