The Transport Control Protocol (TCP) is a low-level part of the protocol stack used by the Internet. It sits directly above the IP layer and is responsible for making sure that dropped packets are resent.

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How can I read lines at a fixed speed?

I need to read a large log file and send it over a local network using (netbsd) netcat between two VMs on the same host workstation. I know that netcat has an interval, but as far as I can tell, the ...
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/dev/tcp not present in Linux

I am porting C/pro*c code from UNIX to Linux. The code is: #define __NFDBIT (8 * sizeof(unsigned long)) #define __FD_SETSIZ 1024 #define __FDSET_LONG (__FD_SETSIZ/__NFDBIT) typedef struct ...
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User associated with a socket

I use ss -p to see TCP sockets information. But process info are not printed for some sockets. Below: $ ss -p4 State Recv-Q Send-Q Local Address:Port Peer Address:Port ESTAB 0 0 ...
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Faster alternatives to lsof

I want to extract the process id of a certain process in order to shut it down. The process is a local web server using a certain port (localhost:3000), and I am currently doing it like this to ...
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How to limit all tcp traffic to the network interface the session was initiated on?

I have an embedded linux system with two network interfaces (lan0, wlan0) that are configured to the same subnet. A server on this system accepts tcp connections on both interfaces. How I can assure ...
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Trying to Open a Port using CentOS

(I'm new to this!) I'm running a virtual server running CentOS. I'm trying to run a server that listens on port 37760. The code I'm running executes successfully, so I run netstat -lptu To show a ...
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How does tcp-keepalive work in ssh?

I am trying to code a shell-script that uses a ssh-connection for doing "heartbeats". I want to terminate the client- and server-side of that connection after a certain timeout (after the connection ...
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What is the formula to determine how much memory a socket consumes under Linux?

I'm doing some capacity planning and I was wondering if there is a formula that I could use to predict (from a memory standpoint) how many TCP connections I could handle on my server. At the moment, ...
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How to run tcptraceroute utility on UNIX machine?

How can I run the tcptraceroute utility on a UNIX machine? I want to run a TCP traceroute for port 80.
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597 views

How can I trigger a script when a certain port becomes available for requests?

I want to trigger a script when port 3000 is opened by a process. The process is a Rails development server, and I just want to be notified when it finishes spinning up and port 3000 starts accepting ...
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socat reliable file transfer over TCP

I am aware of disadvantages of "wait->stop" design, that usually is proposed with netcat: server$ cat test.dat | nc -q 10 -l -p 7878 client$ nc -w 10 remotehost 7878 > out.dat (It's not reliable ...
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minimal TCP MSS in Linux

The TCP MSS in Linux must be at least 88 (include/net/tcp.h): /* Minimal accepted MSS. It is (60+60+8) - (20+20). */ #define TCP_MIN_MSS 88U My question is: where did they come up with ...
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what level of the network stack does tcpdump get its info from?

As I was trying in vain to fix a faulty ethernet controller here, one thing I tried was running tcpdump on the machine. I found it interesting that tcpdump was able to detect that some of the ICMP ...
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Solaris Command to Stop Listening on a Port

I have a legacy application (that I do not control) that occasionally crashes without properly closing the ports it is listening on. Is there a Solaris command to stop listening on a given port, ...
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How to do “netcat” relays properly so that I have more control?

How to use the netcat to have relays? Like following I tried but not working: cd /tmp mknod backpipe p nc -l -p 7007 0<backpipe | nc 192.168.1.101 9001 | tee backpipe I want to receive data on ...
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port redirection with PF under OpenBSD

i need to do a setting a bit unusual. I have 3 machines with public Ips. I want to use one of them as a load balancer for the 2 others. My machine >> machine1 who redirect the connection to machine ...
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SSH tunnel to router periodically hangs. TCP problem?

Something weird I've noticed since upgrading my office router to the Buffalo WZR-HP-G300NH. When I remote in using an SSH tunnel, the tunnel will "freeze" pretty often. The freeze lasts 1-2 minutes ...
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how to check rx ring, max_backlog, and max_syn_backlog size

Quite often in the course of troubleshooting and tuning things I find myself thinking about the following Linux kernel settings: net.core.netdev_max_backlog net.ipv4.tcp_max_syn_backlog ...
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How can I configure a reverse SSH connection to the connecting computer?

I'm going to be deploying a number of machines in the near future which will be behind routers. It won't be feasible to set up dynamic DNS on each router and port forwarding, so is there a way I can ...
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How long is a TCP local socket address that has been bound unavailable after closing?

On Linux (my live servers are on RHEL 5.5 - the LXR links below are to the kernel version in that), man 7 ip says: A TCP local socket address that has been bound is unavailable for some time after ...
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Why are the first 1024 ports restricted to the root user only?

This is more idle curiosity than anything else. A friend of mine asked me 'which port range is it that only root can use under Linux?' I told him 0-1024 were restricted. Then he asked my why it was so ...
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What tools do I need to intercept and change an incoming packet on a WP2-Personal wifi hub

Which tools should I research into to intercept a plain text packet, edit it and then continue it on it's way. I am using Ubuntu 11.04 and Backtrack 5; my wifi is WPA2-person encrypted. I need to edit ...
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How to fake the source-port of a TCP packet?

Is there an easy way (or is it possible at all) to rewrite a TCP packet as it leaves the machine? For example if I run telnet binfalse.de 22 it will search for an unused port to leave the machine. ...
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Bind unprivileged application to privileged port on Mac OS X

I'd like to create launchd.plist file for an httpd server. Problem is - when the httpd is run as privileged user it daemonizes, which is not allowed by launchd.plist manual page. If I don't run it as ...
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Port monitoring on GNU/Linux based NAT router

I am using a Ubuntu machine as a NAT router. How can I find out the following: the ports on which the LAN machines are listening or communicating (both tcp and udp); which local machines have ...
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178 views

vnc over ssh port assignment

At the office I have on the servers a vnc server running. In Windows I use putty to connect to the server, I log in and then use realvnc to see the desktop. But I cannot get this to work on Linux. I ...
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Need further explanation on TIME_WAIT

Hi Unix/Linux Gurus out there! I need a solid proof that TIME_WAIT (a lot of it actually) is the real culprit in the slowdown in one of our servers. The server is hosted on Parallels Baremetal ...
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Select YeAH-TCP like congestion control algorithm to configure kernel

I'm configuring/compiling the 2.6.37 kernel and I want select YeAH-TCP like default congestion control algorithm but, although I enable this option (CONFIG_TCP_CONG_YEAH), it doesn't show in the ...