In macOS 10.12.6
When ssh to a server use the follow command:
ssh -i ~/key.pem ubuntu#123.111.222.101
the connection will keep until I disconnect it manually or the computer fall asleep.
However, when I ssh to the server behind a proxy:
ssh -i ~/key.pem -o ProxyCommand='/usr/bin/nc -x 127.0.0.1:1080 %h %p' ubuntu#123.111.222.101
the connection will disconnect if I don't type any word in the terminal after 30 seconds.
Why this will happen and how to keep the connection?
P.S.: the protocol of my proxy is socks5
Add this option. This should keep the connection open
-o ServerAliveInterval=15
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'm trying to set up an automatic rsync backup (using cron) over an ssh tunnel but am getting an error "Connection to localhost closed by remote host.". I'm running Ubuntu 12.04. I've searched for help and tried many solutions such as adding ALL:ALL to /etc/hosts.allow, check for #MaxStartups 10:30:60 in sshd_config, setting UsePrivilegeSeparation no in sshd_config, creating /var/empty/sshd but none have fixed the problem.
I have autossh running to make sure the tunnel is always there:
autossh -M 25 -t -L 2222:destination.address.edu:22 pbeyersdorf#intermediate.address.edu -N -f
This seems to be running fine, and I've been able to use the tunnel for various rsync tasks, and in fact the first time I ran the following rsync task via cron it succeeded:
rsync -av --delete-after /tank/Documents/ peteman#10.0.1.5://Volumes/TowerBackup/tank/Documents/
with the status of each file and the output
sent 7331634 bytes received 88210 bytes 40215.96 bytes/sec
total size is 131944157313 speedup is 17782.61
Ever since that first success, every attempt gives me the following output
building file list ... Connection to localhost closed by remote host.
rsync: connection unexpectedly closed (8 bytes received so far) [sender]
rsync error: unexplained error (code 255) at io.c(605) [sender=3.0.9]
An rsync operation of a smaller subdirectory works as expected. I'd appreciate any ideas on what could be the problem.
It seems the issues is related to autossh. If I create my tunnel via ssh instead of autossh it works fine. I suspect I could tweak the environment variables that affect the autossh configuration, but for my purposes I've solved the problem by wrapping the rsycn command in a script that first opens a tunnel via ssh, executes the backup then kills the ssh tunnel, thereby eliminating the need for the always open tunnel created by autossh:
#!/bin/sh
#Start SSH tunnel
ssh -t -L 2222:destination.address.edu:22 pbeyersdorf#intermediate.address.edu -N -f
#execute backup commands
rsync -a /tank/Documents/ peteman#localhost://Volumes/TowerBackup/tank/Documents/ -e "ssh -p 2222"
#Kill SSH tunnel
pkill -f "ssh.*destination.address"
I wish to use SSH to establish a temporary port forward, run a local command and then quit, closing the ssh connection.
The command has to be run locally, not on the remote site.
For example consider a server in a DMZ and you need to allow an application from your machine to connect to port 8080, but you have only SSH access.
How can this be done?
Assuming you're using OpenSSH from the command line....
SSH can open a connection that will sustain the tunnel and remain active for as long as possible:
ssh -fNT -Llocalport:remotehost:remoteport targetserver
You can alternately have SSH launch something on the server that runs for some period of time. The tunnel will be open for that time. The SSH connection should remain after the remote command exits for as long as the tunnel is still in use. If you'll only use the tunnel once, then specify a short "sleep" to let the tunnel expire after use.
ssh -f -Llocalport:remotehost:remoteport targetserver sleep 10
If you want to be able to kill the tunnel from a script running on the local side, then I recommend you background it in your shell, then record the pid to kill later. Assuming you're using an operating system that includes Bourne shell....
#/bin/sh
ssh -f -Llocalport:remotehost:remoteport targetserver sleep 300 &
sshpid=$!
# Do your stuff within 300 seconds
kill $sshpid
If backgrounding your ssh using the shell is not to your liking, you can also use advanced ssh features to control a backgrounded process. As described here, the SSH features ControlMaster and ControlPath are how you make this work. For example, add the following to your ~/.ssh/config:
host targetserver
ControlMaster auto
ControlPath ~/.ssh/cm_sockets/%r#%h:%p
Now, your first connection to targetserver will set up a control, so that you can do things like this:
$ ssh -fNT -Llocalport:remoteserver:remoteport targetserver
$ ssh -O check targetserver
Master running (pid=23450)
$ <do your stuff>
$ ssh -O exit targetserver
Exit request sent.
$ ssh -O check targetserver
Control socket connect(/home/sorin/.ssh/cm_socket/sorin#192.0.2.3:22): No such file or directory
Obviously, these commands can be wrapped into your shell script as well.
You could use a script similar to this (untested):
#!/bin/bash
coproc ssh -L 8080:localhost:8080 user#server
./run-local-command
echo exit >&${COPROC[1]}
wait
I have written a small bash script which needs an ssh tunnel to draw data from a remote server, so it prompts the user:
echo "Please open an ssh tunnel using 'ssh -L 6000:localhost:5432 example.com'"
I would like to check whether the user had opened this tunnel, and exit with an error message if no tunnel exist. Is there any way to query the ssh tunnel, i.e. check if the local port 6000 is really tunneled to that server?
Netcat is your friend:
nc -z localhost 6000 || echo "no tunnel open"
This is my test. Hope it is useful.
# $COMMAND is the command used to create the reverse ssh tunnel
COMMAND="ssh -p $SSH_PORT -q -N -R $REMOTE_HOST:$REMOTE_HTTP_PORT:localhost:80 $USER_NAME#$REMOTE_HOST"
# Is the tunnel up? Perform two tests:
# 1. Check for relevant process ($COMMAND)
pgrep -f -x "$COMMAND" > /dev/null 2>&1 || $COMMAND
# 2. Test tunnel by looking at "netstat" output on $REMOTE_HOST
ssh -p $SSH_PORT $USER_NAME#$REMOTE_HOST netstat -an | egrep "tcp.*:$REMOTE_HTTP_PORT.*LISTEN" \
> /dev/null 2>&1
if [ $? -ne 0 ] ; then
pkill -f -x "$COMMAND"
$COMMAND
fi
Autossh is best option - checking process is not working in all cases (e.g. zombie process, network related problems)
example:
autossh -M 2323 -c arcfour -f -N -L 8088:localhost:80 host2
This is really more of a serverfault-type question, but you can use netstat.
something like:
# netstat -lpnt | grep 6000 | grep ssh
This will tell you if there's an ssh process listening on the specified port. it will also tell you the PID of the process.
If you really want to double-check that the ssh process was started with the right options, you can then look up the process by PID in something like
# ps aux | grep PID
Use autossh. It's the tool that's meant for monitoring the ssh connection.
We can check using ps command
# ps -aux | grep ssh
Will show all shh service running and we can find the tunnel service listed
These are more detailed steps to test or troubleshoot an SSH tunnel. You can use some of them in a script. I'm adding this answer because I had to troubleshoot the link between two applications after they stopped working. Just grepping for the ssh process wasn't enough, as it was still there. And I couldn't use nc -z because that option wasn't available on my incantation of netcat.
Let's start from the beginning. Assume there is a machine, which will be called local with IP address 10.0.0.1 and another, called remote, at 10.0.3.12. I will prepend these hostnames, to the commands below, so it's obvious where they're being executed.
The goal is to create a tunnel that will forward TCP traffic from the loopback address on the remote machine on port 123 to the local machine on port 456. This can be done with the following command, on the local machine:
local:~# ssh -N -R 123:127.0.0.1:456 10.0.3.12
To check that the process is running, we can do:
local:~# ps aux | grep ssh
If you see the command in the output, we can proceed. Otherwise, check that the SSH key is installed in the remote. Note that excluding the username before the remote IP, makes ssh use the current username.
Next, we want to check that the tunnel is open on the remote:
remote:~# netstat | grep 10.0.0.1
We should get an output similar to this:
tcp 0 0 10.0.3.12:ssh 10.0.0.1:45988 ESTABLISHED
Would be nice to actually see some data going through from the remote to the host. This is where netcat comes in. On CentOS it can be installed with yum install nc.
First, open a listening port on the local machine:
local:~# nc -l 127.0.0.1:456
Then make a connection on the remote:
remote:~# nc 127.0.0.1 123
If you open a second terminal to the local machine, you can see the connection. Something like this:
local:~# netstat | grep 456
tcp 0 0 localhost.localdom:456 localhost.localdo:33826 ESTABLISHED
tcp 0 0 localhost.localdo:33826 localhost.localdom:456 ESTABLISHED
Better still, go ahead and type something on the remote:
remote:~# nc 127.0.0.1 8888
Hallo?
anyone there?
You should see this being mirrored on the local terminal:
local:~# nc -l 127.0.0.1:456
Hallo?
anyone there?
The tunnel is working! But what if you have an application, called appname, which is supposed to be listening on port 456 on the local machine? Terminate nc on both sides then run your application. You can check that it's listening on the correct port with this:
local:~# netstat -tulpn | grep LISTEN | grep appname
tcp 0 0 127.0.0.1:456 0.0.0.0:* LISTEN 2964/appname
By the way, running the same command on the remote should show sshd listening on port 127.0.0.1:123.
#!/bin/bash
# Check do we have tunnel to example.com server
lsof -i tcp#localhost:6000 > /dev/null
# If exit code wasn't 0 then tunnel doesn't exist.
if [ $? -eq 1 ]
then
echo ' > You missing ssh tunnel. Creating one..'
ssh -L 6000:localhost:5432 example.com
fi
echo ' > DO YOUR STUFF < '
stunnel is a good tool to make semi-permanent connections between hosts.
http://www.stunnel.org/
If you are using ssh in background, use this:
sudo lsof -i -n | egrep '\<ssh\>'