Questions tagged [openssh]

Questions about the OpenSSH implementation of the ssh protocol.

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Why does running sudo systemctl stop ssh over ssh not immediately terminate the ssh session

This question stems out of curiosity, but lets say I currently have an ssh session with a remote computer, and I run the following command: sudo systemctl stop ssh and after running: systemctl status ...
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How to restrict SSH login post ssh-copy-id

Environment:- Server–1 Ubuntu 18.04.6 LTS OpenSSH_7.6p1 Ubuntu-4ubuntu0.7, OpenSSL 1.0.2n 7 Dec 2017 Server-2 Ubuntu 18.04.6 LTS OpenSSH_7.6p1, OpenSSL 1.0.2n 7 Dec 2017 From Server-1 executed ssh-...
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Why does OpenSSH debug2 handshake logging only on some logins, not on every login?

Running Ubuntu 18.04.1 LTS with package openssh-server 7.6p1-4ubuntu0.5 In /etc/ssh/sshd_config is set LogLevel DEBUG2. I get the debug2 log message of the client MACs offering part of handshake: May ...
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disable ssh public key auth when user is expired

Environment is Ubuntu Bionic LTS, I have local user account which is expired, i.e. # chage -l user-test Last password change : Apr 28, 2021 Password expires : ...
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Use NTRU+x25519 key exchange with gpg-agent?

OpenSSH now (as of v9.0) defaults to 'sntrup761x25519-sha512@openssh.com' as its key exchange algortihm. When using gpg-agent (for example, but I don't think necessarily, with an OpenPGP smartcard ...
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Which public key will be added into my ~/.ssh/known_hosts?

I have a RHEL 8.3 server and this is the content in the /etc/ssh folder: [root@192 ssh]# pwd /etc/ssh [root@192 ssh]# tree -a . ├── moduli ├── ssh_config ├── ssh_config.d │   └── 05-redhat.conf ├── ...
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What is the fingerprint ssh is asking for?

$ ssh 192.168.29.126 The authenticity of host '192.168.29.126 (192.168.29.126)' can't be established. ECDSA key fingerprint is SHA256:1RG/OFcYAVv57kcP784oaoeHcwjvHDAgtTFBckveoHE. Are you sure you want ...
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Unable to negotiate with <ip address> port 22: no matching host key type found. Their offer: ssh-rsa,ssh-dss

I am trying to use the command: ssh -i id_rsa root@<ip> This gave me the error as: Unable to negotiate with port 22: no matching host key type found. Their offer: ssh-rsa,ssh-dss Also after ...
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Passwordless SSH not working with Roumenpetrov PKIX-SSH

I have followed http://tech.ciges.net/blog/openssh-with-x509-certificates-how-to/ to use X509 certs for SSH and used Roumenpetrov's PKIX-SSH builds. Still passwordless SSH is not working. From /var/...
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Add port forwarding to a running SSH session

The OpenSSH client has a command line option for port forwarding, used like this: ssh -L localport:server:serverport user@host which will connect to host as user, and at the same time redirecting ...
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SSH to Ubuntu Permission Denied

I freshly installed Ubuntu 20.04.04 on a laptop and performed all necessary steps to enable SSH on it: sudo apt-get update sudo apt-get install openssh-server I am fully aware and verified the IP, ...
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SSH pair key authentication still password required

I have two boards that run linux os: the client runs raspberry os and the server runs ubuntu18.04. On the client, I generate an SSH key-pair using this command: ssh-keygen It prompts me to enter a ...
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Suppressing your IP address from being entered into the known_hosts file in setting up SSH

We just recently set up a password-less connection between two servers. We have security concerns related to the contents of the known_hosts file. Basically the concern is if some one were to gain ...
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Read key properties

I have multiple keys (some private, some public) and I want to get information about them (their length, their type, anything else). Is that possible?
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How to restrict a jump user (into openSSH jumpbox) to only SSH to another server?

My Goal: restrict a jump users (into OpenSSH jumpbox) to only SSH to another server. Users should not be able to list directories, cd or anything else except ssh from jumpbox to another server. What I ...
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Matching both user and host simultaneously in SSH config

So, I have a bunch of machines I manage, where I've aliased each of them for ease of access. This looks like this for each of them in the ssh client config: Host MACHINE-1075 M1075 m1075 1075 User ...
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Increase SSH Connection timeout on server side without permissions

My goal is to increase my ssh connection timeout on my server, where I have limited permisssions. I do not have permission to even read /etc/ssh/sshd_config (nor append/write) and I do not have sudo. ...
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SSH: ProxyJump from user without shell

I have a system user syncoid as $ cat /etc/passwd syncoid:x:993:990::/var/lib/syncoid:/run/current-system/sw/bin/nologin with the following ssh config: $ cat /var/lib/syncoid/.ssh/config Host eve ...
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ssh-keygen: Provide CA passphrase without prompt during signing

I am using ssh-keygen operations similar to the following to sign SSH keys with a SSH CA: # for SSH hosts ssh-keygen -s $CACert -hn $FQDN $HostPubKey # for SSH users ssh-keygen -s $CACert -n $User $...
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How can I transfer my sshd_config changes to the new file during a Debian upgrade?

During a Debian upgrade, a user could be prompted to update their /etc/ssh/sshd_config file: https://superuser.com/questions/1638779/automatic-yess-to-linux-update-upgrade The selected answer here ...
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ssh reads stdin without being asked to

These do not do the same: $ seq 1000000 | (ssh localhost sleep 1; wc -l) 675173 $ seq 1000000 | (ssh localhost sleep 1 </dev/null; wc -l) 1000000 What is the rationale for ssh reading stdin?
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SSH CA signed keys, one accepted, one rejected

I have several CentOS 9 and one CentOS 7 VM. All are configured to trust my SSH CA for Key verification. I can ssh into all of them with key A, but the CentOS 7 VM rejects Key B. I can't seem to ...
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Disable password authentication for SSHwhen using Key

I’m trying to create a practice pentest box and not sure of the configuration needed to achieve one part of it. Let’s say I get a copy of the users private key (id_rsa). If I try and ssh in with the ...
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How does the sshd authentication process work?

In sshd(8) man page: The OpenSSH SSH daemon supports SSH protocol 2 only. Each host has a host-specific key, used to identify the host. Whenever a client connects, the daemon responds with its public ...
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sshd_config ForceCommand is blocking scp

I want to execute certain script on every SSH connection for admin user, for that I have added below lines to sshd_config: Match User admin ForceCommand /etc/my_script.sh Script is getting executed ...
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Using ssh authentication with a custom application

I have a custom command line script that I want the users to access over SSH. For example when the user logs in with ssh user@server the user should be able to interact with the command line ...
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180 views

Changing the Key Exchange Algorithm used by OpenSSH Server

I am trying to SSH to a certain a Linux machine (that's running OpenSSH-Server) from a Cisco IOS XE device. However, I'm getting Jan 08 15:22:39 localhost.localdomain sshd[2041]: Unable to negotiate ...
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Run custom script after logging in, before the banner is shown with ssh

I am running OpenSSH_7.6p1 in Ubuntu 20.4. I want to run a specific script (/usr/local/bin/script.sh) just after logging into SSH. And this script should be run even before showing the ssh banner. ...
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Failed ssh authentication without specific reason

I am running several devices on remote sites. Recently two of them who are deployed for more than one year started to refuse ssh connections. I managed to get low privilege ssh connection to software ...
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298 views

Unsupported option UsePAM even though OpenSSH is PAM-aware

For my ARM-based Linux system, I crosscompiled OpenSSH, as I need to have a ssh server. In my sshd_config file I set the UsePAM option to yes, because I want to use PAM for the authentication (I need ...
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1 answer
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Centos 7.9 ssh connection failure from macbook

Ssh connection failure from macbook. This stopped working after trying to migrate to Centos 8 MacBook-Pro:~ $ ssh -Y -vvv xxxxxxx@152.3.36.72 -p 32 OpenSSH_8.6p1, LibreSSL 2.8.3 debug1: Reading ...
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ssh authorization from id only, without authentication credentials

Numerous sources provide instructions for key-based authentication to an SSH server, rather than password based. In some isolated environments, it is preferable for a server to authorize a user ...
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1 answer
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SSH verbose mode: how to view amount of data transferred without all the "debug1" lines?

In OpenSSH, verbose mode (ssh -v ...) shows some useful statistics on exit (e.g. Transferred: sent 3532, received 3076 bytes, in 5.5 seconds). However, verbose mode also prints lots of debug1: ... ...
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XAUTHORITY environment variable empty in ssh session

When I enter an SSH connection to a Linux host, the XAUTHORITY environment variable is unset. If I run sudo -b, the connection is dropped, unless I add a nohup command immediately after, in which case ...
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Why Linux used memory is growing?

I use Rocky8.5 Linux and I am experiencing growing the size of used memory when I start transferring gigantic files by SCP! Here is the scenario, I have an ESXi in datacenter A and a VM in datacenter ...
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sshd_config match rule Host not working

Trying to add specific rules based on hostnames in sshd_config. UseDNS is set to yes Match Host remote.address.com AuthenticationMethods "publickey" When trying to connect from that ...
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Forget ssh credentials

I'm using an ssh key (with password) to log into a system. It's the default key on my local computer (inside ~/.ssh). I'm using some kind of credential helper (gnome keyring or ssh-agent, not sure ...
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Writing a bash script to sftp with ssh-keys that have a password - SSH_ASKPASS is not working

I am writing a script in bash to sftp files to another server. I have an SSH key with a password as its required. I have tried using SSH_ASKPASS variable but its not working. DISPLAY=: SSH_ASKPASS=/...
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1 answer
539 views

can't SSH from docker container to remote server

on my host server I have my user with generated private and public keys. I have copied public key value to my remote server authorized_keys file. I have mapped new docker container instance to use the ...
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2 votes
1 answer
79 views

Same ssh command gives different results to different local machines

Is this even possible or is there a bug with openssh? I had a problem with a compiler, and to allow the compiler's developer to replicate the result I created a remote server. The crazy thing is me ...
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3 votes
1 answer
823 views

"ssh" works but "sshpass" doesn't - how is this possible?

I configured key pairs for SSH connection. It works but of course asks for the passphrase. ssh user1@10.7.175.143 So now I try to login with sshpass which I have installed. I tried with -p property ...
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1 vote
2 answers
169 views

Enable/Disable OpenSSH daemon on an interface

I have multiple network interfaces like Ethernet, Wifi, WWAN etc. I want to block SSH root login on all interfaces except for the Ethernet one. Is there an interface-based configuration for sshd, like ...
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Weird behaviour of OpenSSH server eating slowly all the available memory

I have a machine running a pgbouncer server and an Open SSH server so clients can enstabilish a tunnel to the server and connect to the database. Now all the clients keep the connection alive for ...
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1 answer
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Copying a file from linux to windows machine using scp with out entering password

Hello i am trying to copy the file from my ubuntu machine to windows machine using scp without entering the password. I have set up the openssh key and followed the steps to enable the password less ...
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182 views

SSH permission denied error on ssh to localhost, freshly reset SSH keys

I'm running into (what I think is) a very odd situation. I was having some trouble connecting a specific user to another host via SSH. So, I thought I'd try a simple re-initialization of all SSH keys ...
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2 answers
150 views

ssh, start a specific shell (ash), and source your environment on the remote machine

This is a kind of follow-up question to this question: ssh, start a specific shell, and run a command on the remote machine?, except more-specifically regarding ash, and focused on the fact that ...
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2 votes
1 answer
51 views

When an SSH authorized key is restricted to command how can the command read the parameters in the call?

Say an authorized key is restricted to the command to test parameters, eg command="bin/testparameters" and the ssh call is: ssh user@host 'some parameters which may include other commands' ...
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after update to openssh to 7.9p1 and openssl to 1.1.1l scripts executed from crontab with OpenSSH_4.3p2, OpenSSL 0.9.8e

after update to openssh to 7.9p1 and openssl to 1.1.1l script executed from crontab with OpenSSH_4.3p2, OpenSSL 0.9.8e. When same script executed manually runs with current version. How this issue ...
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How to enable ssh-rsa in sshd of OpenSSH 8.8?

Since OpenSSH release 8.8 ssh-rsa is disabled in OpenSSH sshd: $ ssh-audit 1.2.3.4 # algorithm recommendations (for OpenSSH 8.8) ... (rec) +ssh-rsa -- key algorithm to ...
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Force host setting group when ssh-ing via IP address

Suppose I have a ~/.ssh/config file with a few settings to apply to Host *.work.example.com but sometimes I need to connect to hosts that doesn't yet have a DNS record. I know of work arounds that are ...
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