Talk:Secure Shell

From ArchWiki
(Redirected from Talk:SSH)
Jump to: navigation, search

X11 forwarding

regarding X11 forwarding: i don't think it is necessary to enable X11Forwarding on the client on a global base: "Enable the ForwardX11 option in ssh_config on the client."

simply specifing -X option to ssh works for me. [The preceding unsigned comment was added 2010-01-11T15:41:54 by Uwinkelvos (Talk | contribs).]

SendEnv

I think we should add something about accent/UTF-8/encoding. Setting SendEnv LANG LC_* in /etc/ssh/ssh_config (client side) would be very useful. —This unsigned comment is by LeCrayonVert (talk) 22 August 2010. Please sign your posts with ~~~~!

Automatically logout all SSH users when the sshd daemon is shutdown.

edit /lib/systemd/system/systemd-user-sessions.service and append network.target to the after line.


[Unit] Description = Permit User Sessions

Documentation = man:systemd-user-sessions.service(8)

After = network.target remote-fs.target


then symlink /lib/systemd/system/systemd-user-sessions.service to /etc/systemd/system/


artomason (talk) 20:32, 7 February 2013 (UTC)

systemd failed to start sshd

It might be good to add, if systemctl status sshd shows that sshd failed, try and run /usr/sbin/sshd. This way if there is a bad configuration option (ie typo in /etc/ssh/sshd_conf), it is listed with line number.

Matyilona200 (talk) 13:45, 16 May 2013 (UTC)


follow_symlinks

The option 'transform_symlinks' does not work anymore, 'follow_symlinks' is the new one.

1. Should we correct that at the autossh section?

2. Should we write that somewhere?

--Greenway (talk) 17:14, 26 April 2014 (UTC)

Are you sure? I've just installed sshfs and the man page still mentions both options as separate functions. If transform_symlinks is really not working anymore, that's more likely a bug that must be reported upstream.
Anyway I'm just mentioning that also the sshfs article would be affected.
-- Kynikos (talk) 03:12, 28 April 2014 (UTC)


Sorry for this discussion and thank you for correcting me. I referred to this question: http://askubuntu.com/questions/75094/sshfs-transform-symlinks-is-broken Anyway I tested both parameters:

1) sshfs bar: foo

-a --> /etc     l
-b --> c/c1     l
-c              d 
--c1            f

2) sshfs -o follow_symlinks bar: foo

-a              d
-b              d
-c              d
--c1            f

(works as expected)

3) sshfs -o transform_symlinks bar: foo

(same as without the option.)

Here' s the wiki explanation

Following symlinks on the server side

The -o follow_symlinks option will enable this.

Making absolute symlinks work

Use the -o transform_symlinks option, which will transform absolute symlinks (ones which point somewhere inside the mount) into relative ones.


--Greenway (talk) 20:38, 28 April 2014 (UTC)

Regenerate host keys

I am using pre-load arch linux image on Raspberry Pi, which had openssh configured, so I want to regenerate new host keys, which could be archived on Debian with

rm /etc/ssh/ssh_host_* && dpkg-reconfigure openssh-server

Do we have equivalent command on Arch? I can't find them on the wiki

 ssh-keygen -t dsa -f /etc/ssh/ssh_host_dsa_key
 ssh-keygen -t rsa -f /etc/ssh/ssh_host_rsa_key
 ssh-keygen -t ecdsa -f /etc/ssh/ssh_host_ecdsa_key

should be enough? Or more setting is required?

Ref:

--Lefthaha (talk) 24 May 2014

AutoSSH as a Service

AutoSSH doesn't like to run as a service without specifying a port. Using -M 0 and -f parameters in combination will result in the service not starting. Also, when starting as a service (-f option) SSH will not look in ~/.ssh for public keys. If you're using key authentication, the public key will need to be specified with the -i parameter. I assume this limitation would also apply when running as a systemd service.

Running AutoSSH this way worked for me for a Socks 5 proxy:

autossh -f -M 1111 -N -i /home/username/.ssh/id_rsa username@server -D 8080

--Twofive0 (talk) 18:24, 12 August 2014 (UTC)

Autossh as a service seems to be a little redundant, since autossh itself is basically just a service to restart ssh when it exits. I was about write a .service file for autossh when I realized I could cut out the middleman entirely:
~/.config/systemd/user/autossh.service
[Unit]
Description=SSH tunnel

[Service]
Type=simple
Restart=always
RestartSec=1min
ExecStart=/usr/bin/ssh -F %h/.ssh/config -N foo@bar

[Install]
WantedBy=default.target
This seems a little nicer to me, but I'm not sure how I would edit the article to include it.
Silverhammermba (talk) 00:32, 12 February 2015 (UTC)

Additional steps to setup Dropbear

Noticed that you need to create some keys before Dropbear will run:

dropbearkey -t dss -f /etc/dropbear/dropbear.dss
dropbearkey -t rsa -s 4096 -f /etc/dropbear/dropbear.rsa

Maybe it's a good idea to chmod this to 600 or something? —This unsigned comment is by MindTooth (talk) 5 December 2014. Please sign your posts with ~~~~!

To note: Not relating to dropbear, but generally #Regenerate_host_keys above suggests the addition of a setup step for that as well. --Indigo (talk) 14:19, 5 December 2014 (UTC)

Allowing SSH Users to Shutdown, Mount, etc. Without Root authentication

Merged from Allow users to shutdown. -- Alad (talk) 20:48, 23 May 2015 (UTC)

The following describes what I did to allow power [EDIT: and mounting] operations on my machine from a SSH login. I'd be very grateful if anyone could tell me if this was correct and if so, I'll add this section to the page and add a link on the polkit examples.

I have a miniature server machine I use at home for automatic backups, and I used WOL to startup without user intervention, however I found out that issuing
systemctl poweroff
and friends works from a tty but from a remote login I get a message starting:
==== AUTHENTICATING FOR org.freedesktop.login1.power-off ====
and asking for a root password. After searching online it seemed that the right thing to do (but I'm not sure) was to write a polkit rule overriding the and place this before the defaults in /etc/polkit-1/rules.d/. Below is my rule:
polkit.addRule(function(action, subject) {
	if (	action.id == "org.freedesktop.login1.power-off" ||
		action.id == "org.freedesktop.login1.power-off-multiple-sessions" ||
		
		action.id == "org.freedesktop.login1.reboot" ||
		action.id == "org.freedesktop.login1.reboot-multiple-sessions" ||
		
		action.id == "org.freedesktop.login1.suspend" ||
		action.id == "org.freedesktop.login1.suspend-multiple-sessions" ||
        
		action.id == "org.freedesktop.login1.hibernate" ||
		action.id == "org.freedesktop.login1.hibernate-multiple-sessions"	) {

		if ( subject.isInGroup("mypowergroup") ){
			return polkit.Result.YES;
	}
}); 

There might be a neater way to do this rather than enumerating all the actions but I don't speak JavaScript. EDIT: See below:

https://gist.github.com/wooptoo/4013294/ccacedd69d54de7f2fd5881b546d5192d6a2bddb

Someone somewhere seemed to mention that polkit rules weren't the right way to go and there was something wrong with integration with logind/systemd but I didn't understand what he really meant and it was in a different context.

Thanks in advance for any advice --Stellarpower (talk) 12:24, 4 May 2015 (UTC)

Disabling root leaves `su`; suggested addition there:

However, this does not disable su, to do that, add users to wheel, and then disable

gpasswd -a $USER wheel

And then uncomment the auth required pam_wheel.so use_uid line in /etc/pam.d/su (src)Jasper1984 (talk) 18:22, 9 January 2017 (UTC)

This has nothing to do with SSH and is already mentioned on the su page. Closing. -- Lahwaacz (talk) 22:13, 9 January 2017 (UTC)
I agree, I think that most people aren't interested in disabling su in this context, not to mention it provides no real security benefit (being able to sudo is nearly the same as being able to su, the top answer of your link even explains this). -- Etskinner (talk) 02:07, 10 January 2017 (UTC)
The above gives su to that user, you'd ssh into another user, which doesn't have wheel and isnt in sudoers. It closes those two avenues to get into root. PermitRootLogin no is misleading, dont be detached from reality, it gives root login.
The attack vector here is a compromised machine on the ssh-ing end here. There is a chance the password is guessable, it makes sense to try prevent that. Probably some other opening, sure, but then closing this hole is hardly much effort, at least if you're using a separate user already.Jasper1984 (talk) 14:44, 10 January 2017 (UTC)
I agree that the attack vector exists, but Lahwaacz is right in saying that that has nothing to do with Secure Shell, and so it shouldn't be included on this page. If someone is truly worried about that attack, best practice is to Secure_Shell#Force_public_key_authentication and/or Secure_Shell#Protecting_against_brute_force_attacks -- Etskinner (talk) 15:45, 10 January 2017 (UTC)