the secure shell (SSH) daemon

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33
votes
1answer
36k views

How does tcp-keepalive work in ssh?

I am trying to code a shell-script that uses a ssh-connection for doing "heartbeats". I want to terminate the client- and server-side of that connection after a certain timeout (after the connection ...
25
votes
2answers
62k views

How can I restart the SSH daemon on Ubuntu?

When I type in service sshd restart I get a sshd: unrecognized service error. I do have, in /etc/ssh/ a file sshd_config that I use to set config. I can also putty into the Ubuntu box (it is remote). ...
16
votes
2answers
2k views

SSH ignores characters after correct password string?

Remote machine 10.10.10.1 has password "asdFGH12" for user named "user". I'm able to log in even if I type in password "asdFGH12dasdkjlkjasdus" or any other characters after the "asdFGH12" string. $ ...
14
votes
2answers
351 views

What is the difference between these two SSHD configs?

1 Match Group GROUPNAME, User *,!root 2 Match Group GROUPNAME User !root My question: What is the difference between #1 and #2 in the SSHD_CONFIG?
12
votes
5answers
896 views

what's the purpose of ssh-agent?

I've read the official definition: ssh-agent is a program to hold private keys used for public key authentication (RSA, DSA, ECDSA). The idea is that ssh-agent is started in the beginning of an ...
9
votes
3answers
34k views

Where are my sshd logs?

I can't find my sshd logs in the standard places. What I've tried: Not in /var/log/auth.log Not in /var/log/secure Did a system search for 'auth.log' and found nothing I've set /etc/ssh/sshd_config ...
9
votes
2answers
15k views

What do the channel numbers in ssh error message refer to?

In the example below what do the channel numbers correspond to? Which are on the server? Which are on the client? $ ssh -L1570:127.0.0.1:8899 root@thehost Password: Last login: Fri Aug 9 ...
9
votes
2answers
873 views

tmux session killed when disconnecting from ssh

Summary: I'm trying to figure out why my tmux session dies when I disconnect from ssh Details: I have tmux installed on an Arch Linux system. When I start a tmux session I can detach from it and ...
8
votes
2answers
7k views

Why does sshd requires an absolute path?

Why does sshd require an absolute path when restarting, e.g /usr/sbin/sshd rather than sshd Are there any security implications? P.S the error message: # sshd sshd re-exec requires execution with ...
8
votes
4answers
1k views

Failing to block brute force ssh with iptables

I'm trying to block (slow down) brute force attacks on my sshd server. I'm following this guide http://www.rackaid.com/resources/how-to-block-ssh-brute-force-attacks/ which basically says I need to ...
7
votes
4answers
2k views

How to debug SSH port forwarding

This is an extension to ssh port forward to access my home machine from anywhere I tried things mentioned there but I am not able to ssh to my machine. Netgear router settings for port forwarding: ...
7
votes
1answer
127 views

Blocking SSH Brute Force attacks on IPv6

I recently had to work with some servers that have an IPv6 connection and I was surprised to find out that fail2ban does not have IPv6 support, neither does denyhosts. Searching on google I found that ...
6
votes
5answers
1k 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 ...
6
votes
3answers
40k views

X client forwarded over SSH “cannot open display: localhost:11.0”

I have enabled X forwarding on remote machine where SSH server is running: # grep -i forward /etc/ssh/sshd_config X11Forwarding yes # On local machine, I have started SSH client with -X flag ...
5
votes
5answers
2k views

How to setup password-less ssh with RSA keys

I am trying to setup a password-less SSH configuration between two machines and am having trouble. There are a ton of howtos out there that I have followed and have had no success. Here are ...
5
votes
1answer
6k views

Fedora 18 - Start sshd on boot

I've just installed Fedora 18, and trying to configure sshd - I used chkconfig but this is only starting sshd when a user is logged in. How do I change so that sshd starts on system boot?
5
votes
1answer
2k views

My reverse-ssh tunnel is using keepalives but they're not helping

I have an ssh client machine picard behind multiple unreliable internet connections - all with NAT. I have my server time, reliable with a static IP. I want to be able to access picard thorugh time. ...
5
votes
2answers
3k views

How to Provide login delay in ssh

I wanted to provide login delay while login through ssh .I tried couple of ways of doing same but couldn't find desired result. I tried steps provided by given link. ...
5
votes
1answer
284 views

Linux: $SSH_CONNECTION is set even without SSHing to the server

I have a remote server and I am writing a script in the server and want it to fire only when I SSH. I thought of using the $SSH_CONNECTION and $SSH_TTY for this purpose. I found out that when I have ...
5
votes
1answer
2k views

Logging ssh remote commands to `bash_history`

SSH allows a remote user to issue some command without interactively logging in to the server, as the last line of ssh usage indicates: usage: ssh [-1246AaCfgKkMNnqsTtVvXxYy] [-b bind_address] [-c ...
4
votes
1answer
11k views

installing fail2ban on CentOS 7

I am using @GarethTheRed 's answer to this question to install fail2ban on a remote CentOS 7 server. I am able to complete all the steps up until tail -f /var/log/fail2ban.log, at which point I get ...
4
votes
2answers
162 views

which config file is openssh sshd using?

Where can i check/verify which config file sshd is using? I know you can change the config file to use by using -f command, but is there a way to echo which config file is currently being used or is ...
4
votes
2answers
2k views

Disable ssh banner for specific users or ips

I've enabled the banner that appears before the password prompt by setting it it sshd_config. However certain users (especially me) really don't need to see the banner (it also screws up a lot of ...
4
votes
1answer
189 views

hosts.allow: %u not working (log username)

I need to keep track of all SSH connections on my server. In my /etc/hosts.allow I have something like this: sshd: ALL : spawn ( echo "`date` from %u %a " >> /var/log/ssh/%d.log ) & where ...
4
votes
2answers
9k views

Change default path for when I SSH in to CentOS server?

I have a CentOS 5.7 web server, and I want to change the default place I land in when connecting using SSH. Currently I land in /home/username, and I want to land in /home instead. I've gone in as ...
4
votes
1answer
2k views

Can sshd restrict client tunnel endpoints to localhost?

Normally an ssh client can request TCP forwarding using the -L command line option. The server can disable this completely using AllowTcpForwarding no. If enabled, the client can request to connect ...
4
votes
1answer
106 views

Accept any private key for authentication

Is it possible to configure OpenSSH (or any other standard sshd) to accept any key offered by a connecting client? EG ssh -i ~/arbitraryKey hostname grants a login shell while ssh hostanme doesn't. ...
4
votes
1answer
509 views

Executing a remote command on SSH connection, before login

I am trying to find a way to execute a specific command when connecting to a server via SSH. By this I mean, the command will execute unconditionally on opening a connection, so this would preferably ...
4
votes
1answer
85 views

Uselogin in sshd_config

I was looking through my sshd_config file and I found this: #Uselogin no I know it's commented but there is no explanation above it and when I google it, I get this: Don't use the traditional ...
4
votes
1answer
400 views

Why did sshd delete my /dev/zero?

When I do lsof +c 0 | grep /dev/zero, I see the following two lines: sshd 19064 root DEL REG 0,4 497862 /dev/zero sshd 19064 root DEL REG 0,4 498725 /dev/zero ...
4
votes
1answer
81 views

Seperate messages of multiple sshds in syslog-ng

Is there a common way of distinguishing between the messages of multiple processes in syslog-ng beside setting different facilities? +1 if filtering and therefore logging in different files would be ...
4
votes
1answer
1k views

How to exclude from a “Match Group” in SSHD?

There is a Match group in the SSHD config: cat /etc/ssh/sshd_config ... Match Group FOOGROUP ForceCommand /bin/customshell ... There are many users on the machine that are in the ...
4
votes
5answers
113 views

Multiline Text Processing : Editing sshd_config

I have multiple blocks at the end of my sshd_config files like theses: Match User FOO ChrootDirectory /srv/www/FOO AllowTCPForwarding no X11Forwarding no ForceCommand internal-sftp ...
4
votes
2answers
591 views

Starting SSH server after VPN starts

I am running an OpenVPN server on Ubuntu 14.04 as well as OpenSSH. I have my SSH server configured to bind to an IP address on my VPN interface. Once my machine boots, binding to that IP fails. ...
3
votes
4answers
245 views

Internet SSH Server Security Considerations

What steps should I take to reasonably secure my linux desktop before opening sshd to the Internet so I can connect from anywhere?
3
votes
3answers
2k 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.
3
votes
1answer
420 views

How to get the public key from sshd server without touching the known_hosts file?

Are there any tricks to get the public key (the line that goes into the known_hosts file after I answered yes after connecting with ssh) of a server?
3
votes
1answer
192 views

How to know which public key was used when someone used passwordless ssh login?

Say for some reason, there is only a "user" account on a shhd server. Everyone has his own private key to ssh to the server, as "user". Then, is there a way to see who is he (during or after his ...
3
votes
1answer
738 views

SSH Public Key authentication - works only after a physical login

I am trying to connect via SSH to my ubuntu server with public key authentication. For some reasons I get an "Permission denied (publickey)." on the client, whenever I execute ssh -i ~/.ssh/id_rsa ...
3
votes
2answers
6k views

Allowing only specific users to login via ssh at one port and others to login via another port

I have the following use case: Need to allow users to login from a secured, trusted network and then allowing a couple (only two) mobile users to login remotely on a Linux Centos machine. I can make ...
3
votes
2answers
129 views

Why does SSH hosts keys differ when connecting if the host_keys are the same?

There are 3 machines: A (from where I connect to B and C), B, and C. B and C have the same SSHD host keys (they have been copied, so they are 100% the same, SSHD has been restarted too, identical ...
3
votes
1answer
34 views

sudo command inside heredoc block in a ssh session is not working

When i use heredoc and put all the commands inside heredoc as, ssh -t -i master.pem cloud-user@$1 <<EOSSH sudo service x restart sudo service y restart EOSSH it throws error as, ...
3
votes
1answer
64 views

Allow SFTP users to create sub-accounts

Environment Ubuntu 14.04.1 LTS server edition OpenSSH_6.6.1p1 Ubuntu-2ubuntu2, OpenSSL 1.0.1f 6 Jan 2014 Current Configuration SFTP password-protected accounts are setup for Alice and Bob. Their ...
3
votes
2answers
782 views

allow only specific users to login via sshd, but refuse connect to non-listed users

I'm running a CentOS server (7.0) and I'd like to login via sshd as a user, not root. So I set PermitRootLogin no in the config file and su - after login. I've received lots of hacking activities and ...
3
votes
1answer
4k views

SSH publickey works for root but not user [duplicate]

Possible Duplicate: Why am I still getting a password prompt with ssh with public key authentication? I'm setting up a remote server. The sshd is configured to use publickey only. There ...
3
votes
2answers
121 views

How to upgrade SSHD without the change of the server key?

So... we need to upgrade the SSHD. How can we do this without having that issue that the people (who are signing in through ssh) would see the message: ...
3
votes
2answers
739 views

Is there an easy way to not log a specific sshd event?

The monitoring tool of my hoster is making regular connections with ssh on port 22 to see or the service is up. This is cluttering my /var/log/messages with this kind of messages: Dec 13 22:20:17 ...
3
votes
1answer
200 views

SSHD Password Feedback (Show Asterisks for Characters)

Is it possible to have SSHD show asterisks for the password characters much like pwfeedback does for sudo? I am using CentOS 6.5. For example:
3
votes
1answer
6k views

Activity Logging Level in SFTP

I'm using CentOS, i have already figured out how to enable the SFTP Logging. After that when i test it by using FileZilla (from User-end) and tail -f /var/log/sftp.log from the Server, all the ...
3
votes
1answer
412 views

Reconfigure login through root ftp (lost ssh access)

My question is twofold. I need to somehow re-enable telnet and/or ssh in a device where I currently only have root ftp access. Also, if I am going about this wrong, please let me know. Details to ...