Mosh: Having a .moshrc (equivalent to .ssh/config) file to be able to specify per-host configs

[lemoinem]

Hi,

I think this would go a long way improving the usability of mosh to be able to have a .ssh/config equivalent.

Unfortunately, ssh complains about unknown directives in .ssh/config so we will need a new file (I also think it's good practice to do so anyway).

The format could be simple (.ssh/config sounds a pretty good example: easy to write, easy to parse).

Useful configs to include: hostname, port, mosh-server, eventually ssh and command (in some weird case). Later: enable/disable OOB data (#423) on a per-host basis.
Some of the configs such as hostname, agent forwarding, X11 forwarding, etc... could actually be extracted from .ssh/config directly.

I think it's much better than aliases because it's seamless and consistent. Plus the fact that mosh already seamlessly use .ssh/config makes it quite irritating to be able to use aliases only for specifying a couple of argument for a given host. If many hosts requires a custom config multiplication of aliases could also clutter the shell. Plus we always have to remember which hosts works out-of-the-box and which needs an alias. All this disappears with a .mosh/config config file.

Security-wise, since it's already done by ssh (and actually allows a much bigger control on the connection since it could change the Hostname we are connecting to, define a ProxyCommand, etc...), If the file is secure, I don't see a very big security issue here.

[lemoinem]

FTR, IRC discussion:

11:40 < lemoinem> I was wondering if there has already been a discussion regarding a .ssh/config-like file for mosh...
11:41 < grawity> What options would it have?
11:41 < lemoinem> I think it's a kind of small feature code-wise that would go a great way to improve the usability.
11:41 < lemoinem> On the top of my head, port is the one I see the most usefull
11:41 < achin> -p is the only useful option to mosh, right?
11:41 < lemoinem> yeah, but mosh-server could be too
11:41 < achin> true
11:42 < achin> in the past, people have recommended aliases for this, but i can see how a .mosh-config might be useful
11:42 < lemoinem> (plus, with oob data coming with mosh 1.3 (iirc), we could enable/disable it on a per-host basis...)
11:44 < lemoinem> otoh, I understand it might still be a bit of work code-wise, but I guess it would already be nice to have it in the roadmap... If enough people think it's a nice idea someone might even contribute to it...
11:44 < lemoinem> I would myself but I don't have the necessary free time on my hands right now )':
11:46 < lemoinem> (per-host ssh command might happen to be useful too in some weird cases...)
11:50 < lemoinem> Oh, another one, having a way to configure the command mosh-server is running (could be useful to have run tmux/screen instead of a direct login shell), but I have a work-around for that already and it's a different feature.
11:50 < joneskoo> basically the reason why config file has not been implemented are security concerns
11:51 < lemoinem> ? security concerns, how come?
11:51 < joneskoo> the current behaviour is simple

[sekrause]

At least for the port I think a _server-side_ configuration file would be much better. Just like SSH has its ~/.ssh/authorized_keys for the user's key we could have a ~/.mosh/ports which defines the ports mosh is allowed to use.

For example if my sysadmin has opened up the UDP port 63210 so that I can use mosh, I simply type echo 63210 >> ~/.mosh/ports (it could also be a port range) and mosh-server will no longer user the ports 60000-61000, but the one defined in the server's configuration file.

[lemoinem]

I'm not sure about having a config file for a single config avery good idea... I think it will tend to multiply the number of config files rather quickly if we ever want other configurations server-side. However, the idea of configuring the port server-side is actually a very good point (:+1:), and could even be configured in a system-wide configuration file.

However, I think it would still be useful to be able to override this client-side in some special cases (SSH Tunnel to reach a FWed host, multiple FW with port translating between the client and the server, etc.

[jgillman]

I'm a little late to the party here, but +1 for a config file.

To connect to my home server I have to type: mosh -p 12345 --ssh="ssh -p 54321 -i ./.ssh/id_rsa" my.host.name

Yes, I can easily alias that but being able to store those the way I would for ssh would be very useful as my config would become more portable. As far as security concerns, I don't see how it would be any less secure than using a .ssh/config file. Plus, it's optional.

[andersk]

mosh already respects SSH options stored in ~/.ssh/config, so there’s no need to pass a long --ssh option every time:

Host my.host.name
    Port 54321
    IdentityFile ~/.ssh/id_rsa

[jgillman]

@andersk So it does! I don't know why I didn't try that. Thanks for the tip :)

[promolic1]

Bumping this issue.

I already know as @andersk said, mosh uses the ssh config file. But what about a custom UDP port? Any workaround to avoid remembering/writing the desired port per host?

[kiniou]

Hi,

I did a simple python3 scripting that does enable profile for mosh ports and commands. It can be found at https://github.com/kiniou/moshy .

[pjrobertson]

Looks like this is in the pipeline!
+1 for this feature.

Currently I have to do

mosh --server=/home/user/bin/mosh-server [email protected]

It would be nice to not have to specify --server :)

[ekacnet]

I did something that works well in my branch config: https://github.com/ekacnet/mosh/tree/config

I made a pull request but so far it seems that it hasn't been pulled.

[infinity0]

Instead of having a separate .moshrc, it would be easier for users, to just put these extra options in .ssh/config?

Host xxx.com.yyy
HostName xxx.com
User uuu
MoshPort 6nnn
MoshPrediction always

[andersk]

@infinity0, nope, the unrecognized syntax would completely break ssh (and therefore also mosh). I could imagine putting them inside magic comments…but not for two seconds longer than I have to.

[emtiu]

Any consensus on this in sight? I'm also very much interested in server-side custom port(range)s. Don't mind if it's systemwide (as in /etc/moshports) or per-user (as in ~/.moshports).

[Toub]

Also interested to have a client-side or server-side configuration for udp port range.

[rgruesbeck]

+1 for this

[Myke]

Another vote for server-side config; with multiple servers behind NAT, ssh-config nicely solves the port changes, but there's no elegant way to teach mosh that it's only getting specific ports forwarded to it.

[yookoala]

+1

There is no way to config custom mosh-server udp port range now.
Would be really handy if a config file is available.

[tjanson]

Please refrain from "+1-ing" issues, here or elsewhere. I’m sure you mean well, but it dilutes the discussion and essentially spams subscribers of the issue.

[ghost]

Great idea, but please avoid polluting home directory, refer to XDG base directory spec.

[dpsenner]

Is there a plan when this feature might be released?

[nepthar]

I know this is an old ticket, but I've noticed that it's still open. Could you provide some guidance as to whether this is still in the works? I have several machines running mosh behind NAT and it would be fantastic if I could configure them server side to use a specified port range.