Questions about the OpenSSH implementation of the ssh protocol.

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14
votes
4answers
13k views

What is the point of sshd “UseDNS” option?

I know what it does, but i don't know why. What attack(s) does it prevent ? Is it relevant for all kind of authentication methods ? (hostbased, password, publickey, keyboard-interactive ...)
2
votes
3answers
1k views

How to limit ssh access for localhost only?

I need to forbid ssh access (except localhost) for specified user. So. ssh localhost should work. ssh hostname from outside should not work for that user. All other users should work as usual.
2
votes
2answers
804 views

SSH public key login: two different keys and SSH_AUTH_SOCK behaviour

A user (user1) on an Ubuntu 12.04 desktop has two SSH RSA keys configured: ~/.ssh/id_rsa and ~/.ssh/id_rsa1 (and .pub files). Both public keys are configured in the authorised keys on the server's ...
0
votes
1answer
277 views

Simple jail for user with open-ssh [duplicate]

Possible Duplicate: Restricting an SSH/SCP/SFTP user to a directory Can I confine my users to their /home/%u directory using simply open-ssh configuration? I did the following from what I ...
4
votes
1answer
396 views

Avoiding duplicate entries in ~/.ssh/known_hosts

I have my DNS search path set to ".intranet", ie, /etc/resolv.conf contains: search intranet When I SSH to a host using a FQDN, like "mailserver.intranet", it adds an entry for ...
4
votes
2answers
1k views

Can ssh_config's ProxyCommand run a local command before connecting to a remote machine?

Before I can to connect to a particular remote machine I have to run a certain local command. So instead of ssh me@remote.machine I have to do local_command ssh me@remote.machine I would like to ...
1
vote
3answers
634 views

Can directory listing be disabled for sftp?

A question arose in a group discussion: Can directory listing be disabled for sftp while still retaining read and write access? We are using openssh on ubuntu server 11.02 if that helps.
5
votes
2answers
7k views

SSH key-based authentication: known_hosts vs authorized_keys

I read about setting up ssh keys in Linux and have some questions. Correct me if I'm wrong… Let's say host tr-lgto wants to connect to host tr-mdm using ssh. If we want to be sure that it's the real ...
3
votes
3answers
2k views

SSH connection freezes after bigger output when inactive for a while

I have a problem with an SSH session freezing after using it again when it was idle for a while. The problem is that the session doesn't freeze immediately, I can still use it. But as soon as a ...
5
votes
1answer
221 views

Public Key Auth + Kerberos

I've setup public key authentication for ssh'ing into my university machine. However, it only logs me in on the local machine and doesn't give me Kerberos credentials which I need for accessing my ...
5
votes
4answers
729 views

ssh command unexpectedly continues on other system after ssh terminates

I'm running the below command, and monitoring the output file on the other system: ssh $ip_address 'for n in 1 2 3 4 5; do sleep 10; echo $n >>/tmp/count; done' If I kill the ssh command ...
2
votes
2answers
1k views

OpenSSH, chroot user: Root needs to own the user directory, is there any consequence?

I want to create an account for my friend on my computer, but I don't want my friend to be able to view all my files. I saw that with OpenSSH, there is an option for that. Inside the SSHD ...
1
vote
3answers
2k views

Can't SSH into Any Server

I work on remote servers frequently, but for some reason I cannot discern, today I am unable to ssh into anything. Everything comes back with Write failed: broken pipe. I know this is a common ...
6
votes
1answer
1k views

how to set the sftp -s subsystem option in a configuration file

The sftp command supports a subsystem option (-s) which allows the remote user to select the remote sftp-server executable, and optionally upgrade to sudo in the process like so; sftp -s ...
2
votes
1answer
300 views

How to setup port redirection after a ssh connection has been opened?

I'm using openssh on both client and server. I know I can run ssh -L or ssh -R to setup some port redirections over ssh. However, since they are command-line parameters, such redirections must be ...
8
votes
2answers
10k views

How do I convert a ssh-keygen public key into a format that openssl PEM_read_bio_RSA_PUBKEY() function will consume?

I'm having an issue generating a public key that the openssl PEM_read_bio_RSA_PUBKEY() function can consume. I keep getting errors. Obviously I cannot simply use the ASCII string in the ssh-keygen ...
2
votes
1answer
517 views

List ports tunnelled on OpenSSH server

Is there any way to list the tunnels that SSH clients connected to my OpenSSH server have set up? I can use e.g. lsof -i to show connections that are being actively tunnelled, but I'd like to be able ...
3
votes
3answers
389 views

How to install openssh in Crux Linux

In Crux Linux I already have installed SSH but when I use ssh-keygen, and try to use the command: ssh localhost to test SSH I get this error: # ssh localhost ssh: connect to host localhost port ...
1
vote
3answers
11k views

How to ssh to remote server using a private key?

I have two servers. Both servers are in CentOS 5.6. I want to SSH from Server 1 to Server 2 using a private key I have (OpenSSH SSH-2 Private Key). I don't know how to do it over unix. But what I did ...
11
votes
1answer
2k views

Limits of SSH multiplexing

I have the following entry in my .ssh/config file Host AAA User BBB HostName CCC ControlMaster auto ControlPath ~/.ssh/%r@%h:%p The above allows me to multiplex multiple ssh ...
1
vote
1answer
154 views

Wrapping socket connections

I'd like to wrap an insecure connection (this one: http://culturedcode.com/things/) with a secure tunnel, a bit like http://en.wikipedia.org/wiki/Stunnel does, just using UNIX tools. What's the best ...
7
votes
3answers
9k views

ssh, start a specific shell, and run a command on the remote machine?

I am in a situation where several users are sharing the same user account on a remote machine. I have a "personal" directory where I wrote my own .zshrc file, and I would like to have a way to: ...
3
votes
1answer
5k views

Can ping but can't do ssh

I am able to ping my friend but not able to do ssh. Why so? He is using a modem. I thought there might be some firewall enabled. I told him to type #iptables -F He did that, but still I am not able ...
0
votes
1answer
341 views

Does OpenSSH_5.9p1 support Chrooted SSH?

Lately i upgraded my SSH server with OpenSSH_5.9p1 and tried to setup chrooted SFTP/SSH. So far i managed to setup chrooted access only for SFTP using new feature of openssh5.9p1: Match User ...
5
votes
4answers
265 views

SSH “sleeping” for a long time before connect? [duplicate]

Possible Duplicate: How to speed my too-slow ssh login? I have a very strange issue with my SSH server. Whenever I attempt to connect, it literally waits about 30 seconds to a minute before ...
4
votes
1answer
658 views

Use different authentication methods for OpenSSH server depending on client IP

I'm sure this has been answered before, but I could not locate the answer with Google, and this search. I currently only allow shared key authentication for openssh server on my box. However, I ...
5
votes
1answer
1k views

All about ssh ProxyCommand

I am looking for an in-depth explanation of the following ProxyCommand, down to the nuts and bolts of its operation, please. Can you kindly completely dissect it for me and improve on it if you can? ...
2
votes
5answers
6k views

ssh server: reasons for sudden “Connection closed by remote host”

One of my ec2 servers has stopped receiving ssh connections. The OS is Ubuntu server 8.04, and the ssh server is the standard openssh-server. After months of uptime, I tried to connet to it today, ...
4
votes
3answers
580 views

Is there a way to run an ssh server on an Android device?

I'm looking to install Debian over my Android installation so as to be able to use openssh-server, as it's so much better than Dropbear. Is there an easy way to do this, or just to simply install ...
4
votes
2answers
2k views

Multiple 'Host *' in ssh_config?

My understanding of the way ~/.ssh/config works is that each 'Host ' line takes effect for any host matching after that point in the config file. I have a number of personal servers and work servers ...
0
votes
1answer
587 views

github ssh problem- permission denied(publickey)

I tried setting up git as shown in Github's help page, on Arch linux but there seems to be some problem with the SSH keys. It gives this error- Permission denied (publickey). This problem is ...
5
votes
2answers
776 views

Should I be backing up my SSH host keys?

In my automated backups, I'm not sure if I should be doing this. If the hard drive fails or if I wipe the hard disk and start over, what will be the effect of starting with a new SSH host key to my ...
3
votes
2answers
2k views

SSH slow at starting session

Starting an Interactive shell over SSH is slow to one of my servers. Everything leading up to it including negotiating encryption is fast, but then it hangs for 45 seconds. After that, it finishes ...
21
votes
3answers
11k views

Restricting an SSH/SCP/SFTP user to a directory

Is there a simple way to restrict an SCP/SFTP user to a directory? All methods that I've come across require me to set a chroot jail up by copying binaries, but I don't think that should be necessary. ...
4
votes
1answer
140 views

I can't ssh on localhost at a certain port on os x

Here are basics information: $ which ssh /opt/local/bin/ssh It's like that because I'm using MacPorts and it did install there. I did the sudo port load openssh When doing a netstat -an | grep ...
2
votes
2answers
2k views

making ssh hosts global to all the users on the computer

So SSH has these files that configure settings for a specific user. ~/.ssh/authorized_keys ~/.ssh/config ~/.ssh/id_rsa ~/.ssh/id_rsa.pub ~/.ssh/known_hosts I'd like to globalise some of these ...
9
votes
4answers
5k views

Given keys in ~/.ssh/authorized_keys format, can you determine key strength easily?

~/.ssh/authorized_keys[2] contains the list of public keys. Unfortunately, each public key does not specify the key strength ( number of bits ). Is there a utility that can process this file line by ...