Programming :: Blocking And Non Blocking TCP Send/recv?
Dec 25, 2010
I have a device that is working on modbus protocol andI have written a small program(with block TCP read method ) to read its registers via modbus protocol.my program is working very well but except those times that I unplug the Ethernet cable or turning off the modbus gateway during programs work.at this time my program stops on recv system call (if it reach this system call exacly when I unplug Ethernet cable or turning off the modbus gateway during programs work).I changed my source to work in nonblock TCP method, at this time with the same situation my program does not stop/block on recv system call but after pluging back the Ethernet cable or resuming the connectivity situation back it reads data incorrectly .this is my code:Quote:
Been trying all sorts of different things to implement a non-blocking send on a TCP server socket.As I kill the client, the server keeps blocking on the send no matter what. Am I missing something? Any other way to do that without involving any additional thread?
I am making a library, but I am facing a strange problem while sending data over network using ethernet.
I am sending 39 bytes of the data from one server to slave application but some time slave receives 39 bytes and some time it receives 29 bytes. And when ever slave receives 29 bytes all the memories to which my pointers are pointing get changed. This problem is only when I am sending data from the server to slave, while sending data from slave to server I am facing no such issue.
I'm just beginning to program with GTK+, and I'm facing this issue: I want to inhibit a signal emission inside one and only one function. I've down cut my code into the smallest example I can to show you what I want to do:The "Emitter" contains a "GtkSpinBox" and it relays the "value-changed" signal, it's header:
I have a SSH server on Ubuntu 10.04 running behind a NAT. I have done the port-forwarding at the router. However say for example I want to restrict people connecting to the SSH server by country IP's. When I configure ufw with the following rule it still lets the IPs that are restricted through. Any idea why
sudo ufw allow from xxx.xxx.xxx.xxx/24 to any port 2556
My ISP (Cox) is blocking port 80 and I would like to know if there is a way to open it again. I am to taking about 8080, 8000 or 81 I want to use 80 so I can host my website and every one can access it without the need to put [url]:[PORT] at the URL
I'm trying to install libbz2-dev on my labtop.I'm running Kubuntu 10.04.Some packages could not be installed. This may mean that you have requested an impossible situation or if you are using the unstable distribution that some required packages have not yet been created or been moved out of Incoming.
I've a CentOS Box with no control panel.. I used to manage it via SSH. Any way, I've installed CSF/LFD on it.. and it seemed to be working just fine. The only problem I've encountered is that when I start and enable CSF, messages and emails keeps stocked in the mail queue.. I've double checked and made sure needed ports are opined.. But, I still have the problem.
I am trying to backup my system with a script I found here. It gives me an error message of invalid blocking factor for --exclude=lost+found I have no idea what this means. I tried to search this form for that message and received no hits.
I can see what Firestarter is blocking in the Firestarter/Events tab, but after reading all the man pages of UFW, I still don't know how to check what the UFW is blocking.
After reading a lot about networking and security I decided to check the security of my own ubuntu box. So I went installing Nmap and discovered that port 139 was "open". Since I 'd read how to use ufw I created a deny rule for port 139. After a second scan with Nmap it still said that port 139 was open as shown below.
I'm trying to use VNC on my headless desktop server that's running lucid, but I can only use SSH because a pop asking me to unlock the keyring shows up every time I try to use VNC. I don't have a monitor for that desktop, so I was wondering, is there any way to remove the keyring/to automatically unlock it during autologin? I don't remember what a site I found it on, but I used this to remove my keyring yesterday. It's no longer working today.
I need assistance blocking application in Ubuntu 10.04. block all applications for certain users if they do not exist in a certain directory.For example,we would like to prevent users from launching a portable copy of Firefox from a portable HDD or Flash drive.
im having a bit of a problem with Firestarter, i have Transmission opened and i am downloading a movie but when i check Firestarter i see hundreds and hundreds of Ip's that are blocked, and like 10ip's every second that get blocked.
I might be misunderstanding the log but it looks like UFW is blocking connections. I want to allow all incoming and outgoing. I guess what I'm saying is that the servers on my computer will open ports but all other ports should respond with closed just like a default Ubuntu install. Trying to use UFW to monitor connections without really doing any firewalling.
I've setup ufw rules on my system but noticed that the rule i created to allow traffic from my local network is still dropping some RST and ACK packets. here's part of the output of dmesg
I want to block all the outgoing ssh form my machine, i.e my machine will not be able to ssh to any outside machine using iptables. The distro is RHEL, I added the following entry in the iptables but unfortunately it didnt worked, -A OUTPUT -p tcp -m tcp --dport 22 -j DROP
i used the angry ip scan software and found alot of the public ip addresses on our network are accessable from outside when they are not suppose to, For eg printers/ pcs etc. to make a start on locking down the network i was wondering if anybody knew th iptables command to add a rule which blocked all incoming traffic to specific ip adresses on the network and to a range of ip addresses.
Where I work we have a lan, it is almost 100% windows machines except for 2 CentOS machines in which some clients connect to, via VPN. (very small network, <50 ip's used)
I would like to know if there is a way to block access from that machines to others in the network. I'm already logging traffic (with IPTraff) to see if they're accessing other machines in the network others than the ones they should connect.
When I turn on my SeLinux to enforcing mode on my Red Hat system ssh stops working and my http server stops responding.
I went into the SeLinux GUI and enabled things in there but still it wont work.
Any thoughts on what to check?
permissive mode and disabled they work
I read several articles that say it should not be affect by SeLinux and the setting look correct but the only thing I do is turn on SeLinux and ssh /httpd stop working
I have a Debian server running at the gateway level on a LAN. This runs squid for creating block lists of websites - for eg. blocking social networking on the LAN. Also uses iptables.
I am able to do a lot of things with squid & iptables, but a few things seem difficult to achieve.
1) If I block http://www.facebook.com, people can still access https://www.facebook.com because squid doesn't go through https traffic by default. However, if the users set the gateway IP address as proxy on their web browser, then https is also blocked. So I can do one thing - using iptables drop all outgoing 443 traffic, so that people are forced to set proxy on their browser in order to browse any HTTPS traffic. However, is there a better solution for this.
2) As the number of blocked urls increase in squid, I am planning to integrate squidguard. However, the good squidguard lists are not free for commercial use. Anyone knows of a good squidguard list which is free.
3) Block yahoo messenger, gtalk etc. There are so many ports on which these Instant Messenger softwares work. You need to drop lots of outgoing ports in iptables. However, new ports get added, so you have to keep adding them. And even if your list of ports is current, people can still use the web version of gtalk etc.
4) Blocking P2P. Haven't been able to figure out how to do this till now.
Ok so, buddy of mine has his ssh server setup and upon checking his logs he sees a ton of failed attempts. Now obviously these are people that are scanning him and trying to brute force him. So is there a way to block them? We know you can block each IP but is there a way to block ALL connections except for certain ones, such as his and mine? Maybe a couple others.
I configured squid in oracle enterprise linux 5.I want to block skype access.i configured the following to block skype.but it is not blocking.acl skype_blocking urlpath_regex [0-9]+.[0-9]+.[0-9]+.[0-9]+ http_access deny skype_blocking
I've been using the denyhosts software for about 8 months to block IPs that are trying to connect to my network that shouldn't be. I'm having trouble with it today for the first time and I can't track down the issue.It is installed on the main server which is the outside IP for the network as well. This should allow me to SSH to the hostname/network IP, or the NAT IP as well. It worked fine up until this morning when I started to work on an ftp server, as far as I know I didn't make any changes that should cause problems.
hosts.deny starts with no 192.x.x.x addresses in it. In allowed-hosts for denyhosts I have entered 192.168.1.1 so that the router should never get blocked.I can SSH to the hostname perfectly fine, connection doesn't drop or anything.If I SSH to the NAT address the connection hangs there while the IP address gets added to hosts.denyI can confirm 100% that I was able to SSH to my NAT from within the network with no problem, now it seems to throw the router IP into hosts.deny if I try to connect from within the network using the NAT.Here is the error that I get in /var/log/securesshd[9272]:d not receive identification string from 192.168.1.1I did update my system recently which may have changed the way some files behave, I will try updating Denyhosts as well. It looked like the address being blocked was an IPv6 since it was showing as:sshd[9201]: refused connect from ::ffff:192.168.1.1 (::ffff:192.168.1.1)
