Commands tagged tcp sorted by votes

Commands tagged tcp (18)

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send echo to socket network

this command will send a message to the socket 25 on host 192.168.1.2 in tcp. works on udp and icmp understand only IP address, not hostname. on the other side (192.168.1.2), you can listen to this socket and test if you receive the message. easy to diagnose a firewall problem or not.
This is sample output - yours may be different.
25

echo "foo" > /dev/tcp/192.168.1.2/25

mobidyc · 2009-09-12 16:48:05 31
Get the time from NIST.GOV

The format is JJJJJ YR-MO-DA HH:MM:SS TT L DUT1 msADV UTC(NIST) OTM and is explained more fully here: http://tf.nist.gov/service/acts.htm Show Sample Output
This is sample output - yours may be different.
```
cat </dev/tcp/time.nist.gov/13

55168 09-12-03 20:32:43 00 0 0 350.2 UTC(NIST) * 
```
8

cat </dev/tcp/time.nist.gov/13

drewk · 2009-12-03 21:40:14 12
Check if port is open on remote machine

Check if port is open, if you don't have ncat on your machine. Show Sample Output
This is sample output - yours may be different.
```
Port is open
```
6

echo > /dev/tcp/127.0.0.123/8085 && echo "Port is open"

jonavon · 2020-05-03 13:30:13 483
send echo to socket network

Using netcat, usuallly installed on debian/ubuntu. Also to test against a sample server the following two commands may help echo got milk? | netcat -l -p 25 python -c "import SocketServer; SocketServer.BaseRequestHandler.handle = lambda self: self.request.send('got milk?\n'); SocketServer.TCPServer(('0.0.0.0', 25), SocketServer.BaseRequestHandler).serve_forever()" Show Sample Output
This is sample output - yours may be different.
```
got milk?
```
2

echo foo | netcat 192.168.1.2 25

pykler · 2009-09-13 01:33:02 4
retrieve the source address used to contact a given host

on multihomed hosts, connected to several networks, could be usefull to know the source address (local ip address) used to reach the target host, this command does not require root priviledges. The command use a TCP socket, if there is any error the command return an empty string, elsewhere return a valid ip address. Show Sample Output
This is sample output - yours may be different.
```
$ python -c 'import socket;  s = socket.socket(socket.AF_INET, socket.SOCK_STREAM); s.connect(("www.google.com", 80)); print s.getsockname()[0] ; s.close() ;' 2> /dev/null
192.168.26.198
```
2

python -c 'import socket; s = socket.socket(socket.AF_INET, socket.SOCK_STREAM); s.connect(("<hostname>", <port>)); print s.getsockname()[0] ; s.close() ;' 2> /dev/null

angleto · 2009-10-13 16:21:15 3
find established tcp connections without using netstat!!

Fast and easy way to find all established tcp connections without using the netstat command.
This is sample output - yours may be different.
2

lsof -i -n | grep ESTABLISHED

techie · 2013-04-03 09:14:09 9
parse and format IP:port currently in listen state without net tools

Useful for containers and environments where you need to know if a port is currently in listen mode but you have not easy way or privileges to install net-tools like netstat or ss. "0A" is the code for listen state. The IP hex is reverse order and all in hex format. Show Sample Output
This is sample output - yours may be different.
```
0.0.0.0:111
10.174.109.1:53
127.0.0.53:53
0.0.0.0:22
127.0.0.1:631
0.0.0.0:8000
```
2

cat /proc/net/tcp | grep " 0A " | sed 's/^[^:]*: $..$$..$$..$$..$:$....$.*/echo $((0x\4)).$((0x\3)).$((0x\2)).$((0x\1)):$((0x\5))/g' | bash

glaudiston · 2020-05-23 12:36:21 156
Windows telnet

Check if TCP port is reacheable Show Sample Output
This is sample output - yours may be different.
```
ComputerName     : ecample.com
RemoteAddress    : 192.168.1.59
RemotePort       : 443
InterfaceAlias   : SRV-37
SourceAddress    : 192.168.1.10
TcpTestSucceeded : True
```
2

Test-NetConnection -ComputerName example.com -Port 443

ebah80 · 2021-09-16 16:11:04 245
tell if a port is in use

if you don't do --numeric-ports, netstat will try to resolve them to names Show Sample Output
This is sample output - yours may be different.
```
tcp        0      0 localhost.localdomain:8321  *:*                         LISTEN
tcp        0      0 ::1:8321                    *:*                         LISTEN
```
1

netstat -a --numeric-ports | grep 8321

peter4512 · 2012-01-20 22:00:56 7
tcpdump whole packets to file in ascii and hex with ip adresses instead of hostname
This is sample output - yours may be different.
1

tcpdump host <IP> -nXXv -s0 -w file.pcap

harpo · 2013-09-04 07:24:04 29
Display any udp/tcp connections by process name or by process id

Where COMMAND is the process(es) name. I prefer to get all states but you may add ESTABLISHED in the grep regex. lsof -c apache2 | egrep -o 'TCP.*ESTABLISHED.*$' -nP flags are optional and UDP is irrelevant for established connections Similar but using the process id: lsof -nP -p PID | egrep -o '(TCP|UDP).*$' Show Sample Output
This is sample output - yours may be different.
```
$ lsof -nP -c apache2 | egrep -o 'TCP.*$' | sort -u
TCP 192.168.0.2:443->192.168.0.136:3373 (ESTABLISHED)
TCP 192.168.0.2:443->192.168.0.137:11127 (ESTABLISHED)
TCP 192.168.0.2:443->192.168.0.137:11153 (ESTABLISHED)
TCP *:443 (LISTEN)
TCP *:80 (LISTEN)

$ lsof -p 17279|egrep -o '(TCP|UDP).*$'
TCP 127.0.0.1:32434 (LISTEN)
UDP *:32435 
```
0

lsof -nP -c COMMAND | egrep -o '(TCP|UDP).*$' | sort -u

forcefsck · 2011-01-25 12:04:13 5
Displays All TCP and UDP Connections
This is sample output - yours may be different.
0

sudo netstat|head -n2|tail -n1 && sudo netstat -a|grep udp && echo && sudo netstat|head -n2|tail -n1 && sudo netstat -a|grep tcp

brando56894 · 2011-09-08 18:54:36 4
One liner to check out CLOSE_WAIT and TIME_WAIT connection every five seconds while debugging network apps

This has saved me many times while debugging timeout issues to "too many open files" issues. A high number of the order of thousand, indicates that somewhere connection is not being closed properly. Show Sample Output
This is sample output - yours may be different.
```
      7
      7
```
0

while true; do netstat -a|grep WAIT|wc -l; sleep 5; done

adimania · 2013-06-19 09:19:41 14
TCP server on one socket

A TCP server that keeps the same socket open, sending the contents of "file" repeatedly.
This is sample output - yours may be different.
0

while true; do cat "file"; done | nc -v -l 1337

bknk · 2014-02-06 03:02:58 7
Show a running count of CLOSE_WAIT and TIME_WAIT connections for debugging network apps

Uses the suggestions by jld on #12421 as well as the new iproute2 tools instead of old net-tools.
This is sample output - yours may be different.
0

watch -n5 ss \| grep -c WAIT

djpohly · 2014-07-30 17:09:08 6
send echo to socket network

you can use a pair of commands to test firewalls. 1st launch this command at destination machine ncat -l [-u] [port] | cat then use this command at source machine to test remote port echo foo | ncat [-u] [ip address] [port] First command will listen at specified port. It will listen TCP. If you use -u option will listen UDP. Second command will send "foo" through ncat and will reach defined IP and port. Show Sample Output
This is sample output - yours may be different.
```
"foo" if it's working
"Ncat: Connection refused." if it's not
```
-1

echo foo | ncat [ip address] [port]

dragonauta · 2012-10-26 10:53:47 7
Monitoring TCP connections number

Monitoring TCP connections number showing each state. It uses ss instead of netstat because it's much faster with high trafic. You can fgrep specific ports by piping right before awk: watch "ss -nat | fgrep :80 | awk '"'{print $1}'"' | sort | uniq -c" Show Sample Output
This is sample output - yours may be different.
```
      3 CLOSE-WAIT
      1 CLOSING
   1013 ESTAB
      6 FIN-WAIT-1
     29 FIN-WAIT-2
     20 LISTEN
      1 State
    323 TIME-WAIT
```
-1

watch "ss -nat | awk '"'{print $1}'"' | sort | uniq -c"

ricardofunke · 2012-12-07 19:07:33 9
tiny proxy in shell to receive on port and write on unix socket

* Make a FIFO file named replypipe * listen on 1234 * pass the request to unix socket * unix socket will reply to replypipe * replypipe will write reply to the client
This is sample output - yours may be different.
-1

mknod replypipe p; nc -k -lp 1234 < replypipe| nc -U /var/run/mysocket.sock > replypipe

adimania · 2014-07-19 18:17:35 7

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list block devices

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Find usb device in realtime

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Suppress output of loud commands you don't want to hear from

This works even if there are spaces in any word in the command line.

Watch the size of a directory using figlet

You can substitute /home/$USER with any path you like.

remove recursively all txt files with number of lines less than 10

Fast portscanner via Parallel

Which processes are listening on a specific port (e.g. port 80)

swap out "80" for your port of interest. Can use port number or named ports e.g. "http"

Redirect STDIN

Several times, I find myself hitting my up arrow, and changing the search term. Unfortunately, I find myself wasting too much time typing: $ grep kernel /var/log/messages Redirecting STDIN allows me to put the search term at the end so I less cursor movement to change what I'm searching for: $ < /var/log/messages grep kernel If you're using the emacs keyboard binding, then after you press your up arrow, press CTRL+w to erase the word. If this has already been submitted, I couldn't find it with the search utility.

Push a directory onto the stack

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Commands tagged tcp (18)

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