My Ubuntu VPS sometimes becomes unresponsive and inaccessible via SSH. When I use the "Emergency Console" provided by Rackspace I see a garbled screen like this:
A hard reboot seems to be the only way to fix the problem.
This happens every few weeks. Does anyone know what might be causing it?
I try to block the user sandbox from accessing the network with this command:
$ iptables -A OUTPUT -m owner --uid-owner sandbox -j DROP
However, after that I'm still able to ping an external host:
$ sudo -u sandbox ping 206.190.36.45
PING 206.190.36.45 (206.190.36.45) 56(84) bytes of data.
64 bytes from 206.190.36.45: icmp_req=1 ttl=49 time=802 ms
64 bytes from 206.190.36.45: icmp_req=2 ttl=49 time=791 ms
What am I doing wrong?
My configuration looks like this:
$ /sbin/iptables -L
Chain INPUT (policy ACCEPT)
target prot opt source destination
Chain FORWARD (policy ACCEPT)
target prot opt source destination
Chain OUTPUT (policy ACCEPT)
target prot opt source destination
DROP all -- anywhere anywhere owner UID match sandbox
Apparently ping has setuid root set. I just had to remove it:
chmod u-s /bin/ping
Can I tell SSH to send the data only after pressing enter or tab, and not after each individual keypress?
I would like to enable and use the pktgen module on Ubuntu Server. I have enabed the module by adding a line containing 'pktgen' to the /etc/modules file. After rebooting it seems that the module is successfully loaded because the directory /proc/net/pktgen exists.
However when trying to run the first sample I get these errors:
root@ubuntu:~# bash ./pktgen.conf-1-1
Removing all devices
Adding eth4
Setting max_before_softirq 10000
Configuring /proc/net/pktgen/eth4
./pktgen.conf-1-1: line 9: /proc/net/pktgen/eth4: No such file or directory
cat: /proc/net/pktgen/eth4: No such file or directory
cat: /proc/net/pktgen/eth4: No such file or directory
./pktgen.conf-1-1: line 9: /proc/net/pktgen/eth4: No such file or directory
cat: /proc/net/pktgen/eth4: No such file or directory
cat: /proc/net/pktgen/eth4: No such file or directory
./pktgen.conf-1-1: line 9: /proc/net/pktgen/eth4: No such file or directory
cat: /proc/net/pktgen/eth4: No such file or directory
cat: /proc/net/pktgen/eth4: No such file or directory
./pktgen.conf-1-1: line 9: /proc/net/pktgen/eth4: No such file or directory
cat: /proc/net/pktgen/eth4: No such file or directory
cat: /proc/net/pktgen/eth4: No such file or directory
./pktgen.conf-1-1: line 9: /proc/net/pktgen/eth4: No such file or directory
cat: /proc/net/pktgen/eth4: No such file or directory
cat: /proc/net/pktgen/eth4: No such file or directory
./pktgen.conf-1-1: line 9: /proc/net/pktgen/eth4: No such file or directory
cat: /proc/net/pktgen/eth4: No such file or directory
cat: /proc/net/pktgen/eth4: No such file or directory
Running... ctrl^C to stop
Done
It turns out the script simply unable to write a file to the /proc/net/pktgen directory. When I try this manually it fails as well:
root@ubuntu:~# cd /proc/net/pktgen/
root@ubuntu:/proc/net/pktgen# touch eth4
touch: cannot touch `eth4': No such file or directory
Can anyone help me make it work?
I'm using Ubuntu version: 2.6.32-21-server.
Fixed
I apologize for keeping this post not up to date. I was able to fix it. If I remember well the cause of the error was that eth4 did not exist, or did not have the 'online' status.
Anyway, it is fixed now.
I'm working on an application that does network traffic generation. The application has eth1 in promiscous mode. So it directly handles all incoming and outgoing traffic.
One of the features I'm implementing is IP fragmentation and defragmentation. Incoming fragments need to be reassembled, and outgoing packets need to be fragmented if their sizes exceed the MTU of 1500 bytes.
One simple way of testing my application is by sending a ping command to the IP address of eth1:
ping -c1 -s 20000 10.3.2.1
This is working fine.
However, once the packet size exceeds ~53000 bytes it fails. According to Wireshark I receive fragments until fragment offset ~51000 and then nothing, followed by a reassembly timeout.
The maximum size of an IP packet is 65535 bytes. The ping command allows specifying a size up until 65507. This actually works if I ping to eth0 (OS controlled).
When inspecting the application from the inside with GDB all is going well. Stepping through the code reveals that the fragments enter my application, the IP packet is succesfully reassembled and then fragmented again, and the fragments are sent back to the sender. Even for the last fragment the return value of send(...) (socket API) is equal to the size of the fragment, indicating success.
Does anybody have an idea what could be going wrong?
Operating system is Linux (based on RTLinux).
The situation is as follows:
I am renting a dedicated server using SliceHost. On this server I have installed a small HTTPServer. I can verify that it works by nativating directly to its IP address (example).
I have also purchased a domain name from gandi.net and would like to link it with to my server. However, I'm having much trouble finding clear instructions on how to create this link. After a few hours of reading documentation and trying out things I ended up the following configuration.
But it doesn't seem to work. I end up on this page telling me the domain name is not available.
Does anyone have an idea what I am doing wrong?
I am testing the Certificate Revocation functionality of a CMTS device. This requires me to setup a OCSP responder. Since it will only be used for testing I assume that the minimal implementation provided by OpenSSL should suffice.
I have extracted the a certificate from a cable modem, copied it to my PC and converted it to the PEM format. Now I want to register it in the OpenSSL OCSP database and start a server.
I have completed all these steps, but when I do a client request my server invariably responds with "unknown". It seems to be completely unaware of my certificate's existence.
I would greatly appreciate if anyone would be willing to have a look at my code. For your convenience, I have created a single script consisting of a sequential list of all used commands, from setting up the CA until starting the server: http://code.google.com/p/stacked-crooked/source/browse/trunk/Misc/OpenSSL/AllCommands.sh
You can also find the custom config file and the certificate that I am testing with: http://code.google.com/p/stacked-crooked/source/browse/trunk/Misc/OpenSSL/
Any help would be greatly appreciated.
Can anyone recommend a free and simple OCSP server for Windows or Linux?
