I am trying to transfer my console application written in ncurses under the terminal connected to the com port to the virtual terminal using telnetd.
When you try to start telnetd, you get: telnetd: getpeername: Socket operation on non-socket. When connected via putty, the connection crashes. netstat shows:
netstat
telnetd expects to be started via inetd. See http://www.qnx.com/developers/docs/7.0.0/index.html#com.qnx.doc.neutrino.user_guide/topic/tcpip_Daemons.html for information on how to set up inetd on QNX.
Related
Background
I have a machine in production running an elixir application (no access to iex, only to erl) and I am tasked with running an analysis on why we are consuming so much CPU. The idea here would be to launch observer, check the processes tab and see the processes with the most reductions.
How am I connecting?
To connect I am following a tutorial from a blog:
https://sgeos.github.io/elixir/erlang/observer/2016/09/16/elixir_erlang_running_otp_observer_remotely.html 1
Their instructions are as follows:
launch the app in the production machine with a cookie and a name
from local run: ssh user#public_ip "epmd -names" to get the name of the app and the port used
from local create a ssh tunnel to the remote machine: ssh -L 4369:user#public_ip:4369 -L 42877:user#public_ip:42877 user#public_ip (4369 is the epmd port by default, 42877 is the port of the app)
from local connect to the remote machine using the node's name: erl -name "user#app_name" -setcookie "mah_cookie" -hidden -run observer
Problem
And now in theory I should be able to use observer on the machine. Instead however I am greeted with the following error:
Protocol ‘inet_tcp’: register/listen error: epmd_close
So, after scouring the dark side of internet, I decided to use sudo journalctl -f to check all the logs of the machine and I found this:
channel 3: open failed: administratively prohibited: open failed
my_app_name sshd[8917]: error: connect_to flame#99.999.99.999: unknown host (Name or service not known)
/scripts/watchdog.sh")
my_app_name CRON[9985]: pam_unix(cron:session): session closed for user flame
Where:
erlang -name: my_app_name
machine user: flame
machine public ip: 99.999.99.999 (obviously not real)
so it tells me, unknown host ?? I am confused since 99.999.99.999 is the public IP of the machine itself!
Questions
What am I doing wrong?
I read that in older versions of erlang I can’t monitor a machine with observer if they are in different networks (which is the case, because I want to monitor this machine from my localhost) but I didn’t find any information regarding this in modern days.
If this is in fact impossible, what alternatives do I have?
Solution
After 3 days of non-stop searching, I finally found something that works.
To summarize I am putting it here everything I did.
All steps in local machine:
get the ports from the remote server:
> ssh remote-user#remote-ip "epmd -names"
epmd: up and running on port 4369 with data:
name super_duper_app at port 43175
create a ssh tunel with the ports:
ssh remote-user#remote-ip -L4369:localhost:4369 -L43175:localhost:43175
On another terminal in your local machine, run a iex terminal with the cookie the app in your remote server is using. Then connect to it and start observer:
iex --name observer#127.0.0.1 --cookie super_duper_cookie
Node.connect :"super_duper_app#127.0.0.1"
> true
:observer.start
With observer started, select the machine from the Nodes menu.
Possible setbacks
If you have tried this and it didn't work there are a few things you can check for:
Check if the EPMD port on your local machine is free, if not, kill the process using it and free it.
Check your ssh tunneling keys and configurations for permissions. As #Roberto Aloi pointed out this link can be useful: https://unix.stackexchange.com/questions/14160/ssh-tunneling-error-channel-1-open-failed-administratively-prohibited-open
In Domino Designer 9 I try to debug a Java agent, for this i followed this steps:
http://www.bizzybee.be/2013/01/11/debugging-java-code-in-domino-designer-8-5-or-9/
I have as port : 8000
In my commandprompt if I do netstat -a I can see that port 0.0.0.0:8000 is LISTENING.
In my notes ini i have the following:
JavaEnableDebug=1
JavascriptEnableDebug=1
JavaDebugOptions=transport=dt_socket,server=y,suspend=n,address=8000
Or sometimes I only put
JavaEnableDebug=1
But I keep getting the error Server connection failed:
How can I connect the debugger??
Though browsing several websites and here on stack overflow, there seems to be a way to view the messages in an Activemq queue using Jolokia and Hawt.io, but I have been unsuccessful to this point.
We are running our Activemq (version 5.12.0) as in embedded service in our Spring Webapp and exposed the Jolokia web services as explained in this webpage:
https://jolokia.org/reference/html/agents.html#agent-war-programmatic
When looking that the Jolokia web services via Hawt.io, I can not figure out how to actually view the messages in the queue.
Here is a screenshot showing the queue size:
So, how can I view the messages in an Activemq queue using Jolokia and Hawt.io?
The solution we ended up going with didn't actually use Jolokia or Hawt.io.
We ended up using Jconsole.
When looking at ActiveMQ queues, if you used a java serialized object in the queue, the data won't be very readably, but if you serialize your object to json, it is quite easy to see what is in the queue.
It is terribly important to read these directions all the way though, carefully.
These instructions discuss SSH Tunneling and it is quite easy to mess something up and there are not very good log messages when things go wrong.
Remote Debugging
Due to security reasons, we have closed all the open debug ports on our remote virtual machines.
To get remote debugging to work, we will need to use SSH Tunneling to access the remote virtual machine debugging ports.
Remote Application Setup
The application that you want to remotely debug must have the JPDA Transport connector enabled.
After Java 1.4, to enable the JPDA Transport, add the following vm parameter when starting your java virtual machine:
-agentlib:jdwp=transport=dt_socket,server=y,suspend=n,address=<remote_port_number>
The above attributes are hard to describe, but what is presented above works well. More information about the above attributes can be found on the Connection and Invocation Details page.
Local IDE Setup
In Intellij to connect to a remote java virtual machine, open the "Run/Debug Configurations" window.
Then select a new "Remote" configuration.
Enter the following values:
Debugger mode
Attach to remote JVM
Host
localhost
Port
<local_port_number>*
Use module classpath
<local_package>**
The <port_number> should be the local port number of the ssh tunneling session that you will be starting. It is recommended that the <remote_port_number> and the <local_port_number> are the same value.
** This value should be whatever your local project is named.
SSH Tunneling
To actually connect to the remote debugging port, we'll need to use SSH Tunneling.
Run the following command via a terminal command line:
$ ssh -L <local_port_number>:localhost:<remote_port_number> -f <username>#<remote_server_name> -N
Example:
$ ssh -L 10001:localhost:10001 -f <your_username>#<your.server.com> -N
This command does the following:
Starts an ssh session with the <remote_server_name>.
Connects your <local_port_number> to the <remote_port_number> of the localhost of the remote machine. In this case, we're saying connect to localhost:10001 of the <your.server.com> machine.
Start remote debugging in the Intellij IDE and you should then be connected to the remote java virtual machine.
Resources
Intellij IDEA remotely debug java console program
Remote debug of a Java App using SSH tunneling (without opening server ports)
Remote JMX
We use JMX to look at the Spring Integration Kaha DB Queues.
Remote Application Setup
Add the following vm parameters:
-Dcom.sun.management.jmxremote.port=64250
-Dcom.sun.management.jmxremote.rmi.port=64250
-Dcom.sun.management.jmxremote.authenticate=false
-Dcom.sun.management.jmxremote.ssl=false
-Djava.rmi.server.hostname=127.0.0.1
The jmxremote.port and jmxremote.rmi.port can be any number and they can be different values, it just helps if they are the same value when doing the ssh tunneling below.
SSH Tunneling
$ ssh -L 64250:localhost:64250 -f <your_username>#<your.server.com> -N
JConsole Setup
This is done in a new terminal window.
$ jconsole -J-DsocksProxyHost=localhost -J-DsocksProxyPort=64250 service:jmx:rmi:///jndi/rmi://127.0.0.1:64250/jmxrmi
Resources
Why Java opens 3 ports when JMX is configured?
Clean Up
To close the ssh processes above:
$ lsof -i tcp | grep ^ssh
Then perform a kill on the process id.
Using jps and jstack to Help Debug
List all java processes running on a machine:
$ sudo jps
List the threads of an application running:
$ sudo -u <process_owner> jstack <process_id>
Example:
$ sudo -u tomcat jstack <pid>
I want to debug a process running on a remote box from my host box (I built the code on the host machine).
Both have linux type operating systems.
I seems I can only communicate to the remote box from the host box via ssh (I tested using telnet).
I have followed the following steps to set this up:
On the Remote box:
Stop the firewall service:
service firewall_service stop
Attach the process to gdbserver
--attach :remote_port process_id
On the Host box:
Set up port forwarding via ssh
sudo ssh remote_username#remote_ip -L host_port:localhost:remote_port
-f sleep 60m
Set up gdb to attach to a remote process:
gdb file.debug
(gdb) target remote remote_ip:remote_port
When I try to start the debugging on the host by running 'target remote remote_ip:remote_port' on the host box I get a 'Connection timedout' error.
Can you guys see anything I am doing wrong, anything to check or an alternative way to debug remotely over ssh I would be grateful.
Thanks
This command:
sudo ssh remote_username#remote_ip -L host_port:localhost:remote_port ...
forwards local host_port to remote_port on remote_ip's localhost. This is useful only if you could not just connect to remote_ip:remote_port directly (for example, if that port is blocked by firewall).
This command:
(gdb) target remote remote_ip:remote_port
asks GDB to connect to remote_port on remote_ip. But you said that you can only reach remote_ip via ssh, so it's not surprising that GDB times out.
What you want:
ssh remote_username#remote_ip -L host_port:localhost:remote_port ...
(gdb) target remote :host_port
In other words, you connect to local host_port, and ssh forwards that local connection to remote_ip:remote_port, where gdbserver is listening for it.
I would like to connect to my raspberry pi using a MobaXterm to play with it from any computer, here how I started to make that work... I try to connect via MobaXterm using windows 8. My windows and my raspberry are both connected on a wifi network using the same netgear wn3000rp, it's a wifi extender.
When i create a ssh tunnel to my raspberry MobaXterm ask me to login to the raspberry, it process and then i receive this answer :
Connection refused
thank for your answer
Seems your port is being used.
If you don't have lsof already you can download and install it by becoming root and running:
root#machine:~# apt-get install lsof
To discover the process name, ID (pid), and other details you need to run:
lsof -i :port
So to see which process is listening upon port 24 we can run:
root#machine:~# lsof -i :24
After this you should be able to move on towards a solution.