SshSession::connect_mux hangs on MacOS 14.5

[justin-elementlabs]

When running the example code, Rust will print "SSH before" but fail to print "SSH after". After a while, I will see a warning about my test "has been running for over 60 seconds". It will continue hang with no error or further output.

Am I missing libraries on my machine? Are there other suggestions on how to find out what is causing this to hang? The russh crate has the same issue.

println!("SSH before"); let result = SshSession::connect_mux( format!( "ssh://{}@{}:{}", &credentials.username, &credentials.host, &credentials.port ), KnownHosts::Add, ) .await; println!("SSH after");

[NobodyXu]

sshsession::connect_mux is usually used when you already creates a ssh multiplex master.

Usually you want to use SessionBuilder

[justin-elementlabs]

@NobodyXu , thanks for the tip. Maybe you could help with a full example? This is what I have right now.

It's hanging after printing "SFTP 201".

If I run ps -ax | grep ssh I do see

ssh -E .../.local/state/.ssh-connectionbb4jRB/log -S .../.local/state/.ssh-connectionbb4jRB/master -M -f -N -o ControlPersist=yes -o BatchMode=yes -o StrictHostKeyChecking=accept-new -p 22 -l ... -o IdentitiesOnly=yes -I ... ssh://...

 let mut b = SshSessionBuilder::default();
b.keyfile("...");
let dest = format!(
    "ssh://{}@{}:{}",
    &credentials.username, &credentials.host, &credentials.port
);
let (b, d) = b.resolve(&dest);
println!("SFTP 201");

let temp_dir = b.launch_master(&dest).await; // What do I do with temp_dir?
println!("SFTP 202");

let result = SshSession::connect(&dest,
    KnownHosts::Add,
)
.await;
println!("SFTP 203");
if result.is_err() {
    return Err(format!(
        "Unable to connect to SSH server at {}:{} (error: {})",
        &credentials.host,
        &credentials.port,
        result.err().unwrap()
    ));
}
println!("SFTP 204");

let ssh_session = result.unwrap();

let result = _Sftp::from_session(ssh_session, Default::default()).await;
if result.is_err() {
    return Err(format!(
        "Unable to establish to SFTP session from SSH session at {}:{} (error: {})",
        &credentials.host,
        &credentials.port,
        result.err().unwrap()
    ));
}
println!("SFTP 220");

[NobodyXu]

Connecting is quite simple:

let session = SshSessionBuilder::default()
    .keyfile("...")
    .connect_mux(format!(
        "ssh://{}@{}:{}",
    &credentials.username, &credentials.host, &credentials.port
)).await?;

[justin-elementlabs]

It's still hanging following the example provided after SFTP 201:

println!("SFTP 200");

let mut b = SshSessionBuilder::default();
let b = b.keyfile("...");
let dest = format!(
    "ssh://{}@{}:{}",
    &credentials.username, &credentials.host, &credentials.port
);

println!("SFTP 201");
let result = b.connect_mux(&dest).await;
println!("SFTP 202");

if result.is_err() {
    return Err(format!(
        "Unable to connect to SSH server at {}:{} (error: {})",
        &credentials.host,
        &credentials.port,
        result.err().unwrap()
    ));
}
println!("SFTP 209");

let ssh_session = result.unwrap();

let result = _Sftp::from_session(ssh_session, Default::default()).await;
if result.is_err() {
    return Err(format!(
        "Unable to establish to SFTP session from SSH session at {}:{} (error: {})",
        &credentials.host,
        &credentials.port,
        result.err().unwrap()
    ));
}
println!("SFTP 220");

[justin-elementlabs]

If I run ps -ax | grep ssh I do see

ssh -E .../.local/state/.ssh-connectionbb4jRB/log -S .../.local/state/.ssh-connectionbb4jRB/master -M -f -N -o ControlPersist=yes -o BatchMode=yes -o StrictHostKeyChecking=accept-new -p 22 -l ... -o IdentitiesOnly=yes -I ... ssh://...

But Rust just hangs

[NobodyXu]

I think it might be the ssh multiplex master that is hanging, maybe that the remote host is hanging somehow?

Can you login to the remote host using ssh on cmdline?

[justin-elementlabs]

@NobodyXu , yes I can ssh fine using command line.

[NobodyXu]

So multiplex master is not working for some reason...

Can you try connecting to the multiplex master directly, using ssh?

[justin-elementlabs]

@NobodyXu , yes this works:

ssh -S /.../.local/state/.ssh-connectionyNAAbu/master ip

[NobodyXu]

Can you try:

let session = SshSessionBuilder::default()
    .keyfile("...")
    .connect(format!(
        "ssh://{}@{}:{}",
    &credentials.username, &credentials.host, &credentials.port
)).await?;

Maybe it's the openssh-mux-client not working?

[justin-elementlabs]

@NobodyXu
It's the same unfortunately. It will hang when connect is called and only print SFTP 201

println!("SFTP 201");
let result = SshSessionBuilder::default().keyfile("...").connect(&dest).await;
println!("SFTP 202");

[NobodyXu]

Ok I think I misunderstood the issue.

It actually stucks in launch_master, it's likely the ssh command never exits.

We expect the ssh to fork and create a server process in background, and then returns.

It's likely not the case here.

[NobodyXu]

ssh -E .../.local/state/.ssh-connectionbb4jRB/log -S .../.local/state/.ssh-connectionbb4jRB/master -M -f -N -o ControlPersist=yes -o BatchMode=yes -o StrictHostKeyChecking=accept-new -p 22 -l ... -o IdentitiesOnly=yes -I ... ssh://...

@justin-elementlabs if you execute this command manually, does it exit immediately or stuck?

[justin-elementlabs]

@NobodyXu it will run for 1-2 seconds and then return to the terminal (exit immediately)

% ssh -E .../.local/state/.ssh-connectionbb4jRB/log -S .../.local/state/.ssh-connectionbb4jRB/master -M -f -N -o ControlPersist=yes -o BatchMode=yes -o StrictHostKeyChecking=accept-new -p 22 -l ... -o IdentitiesOnly=yes -I ... ...

(1-2 seconds later with no more user input...)

%

[NobodyXu]

In openssh, we just wait for the procees to exit and check its status https://docs.rs/openssh/latest/src/openssh/builder.rs.html#487

Given that we are using tokio::process, I think something might be wrong with it? @justin-elementlabs

[NobodyXu]

Which tokio version are you using?

And what is the kernel (linux or macOS)?

I strongly suspect it's a bug in tokio

[justin-elementlabs]

[[package]]
name = "tokio"
version = "1.38.0"

macOS 14.5

[NobodyXu]

I recommend to update to latest tokio (1.39.2), if it still doesn't work, it could be a tokio bug, try launching that ssh command using tokio::process directly, if that stucks with tokio but not your cmdline, then it could be a tokio bug.

[justin-elementlabs]

@NobodyXu , upgrading tokio didn't help. I created an issue just FYI: tokio-rs/tokio#6770

[sander2]

@justin-elementlabs assuming that this is still an issue, I think it might be caused by you using executor::block_on: https://github.com/elementlabs42/BitVM-playground/blob/e102f23d88fee5c46f8e6f86442f371e857016ba/src/bridge/client/data_store/sftp.rs#L208 .If you call the function from a regular async function in a tokio context it works for me

[NobodyXu]

If block_on causes it to fail, then maybe you can try tokio::spawn and then block_on the handler?