Terminate remote ssh command upon disconnect

Question

I'm using Mina SSHD client to run remote commands on OpenSSH server. I'm executing a long running command on the remote server, and would like it to terminate when the client session is closed.

when I run this command from my PC terminal:

\#ssh -t user@server sleep 12345

This what I find on the remote machine:

\# ps -axf

---- Omitted for clarity

12158 ?        Ss     0:29 /usr/sbin/sshd -4
22708 ?        Ss     0:11  \\_ sshd: user@pts/3,pts/4
16894 pts/3    Ss     0:00  |   \\_ -bash
17750 pts/3    R+     0:00  |   |   \\_ ps -axf
17606 pts/4    Ss+    0:00  |   \\_ sleep 12345

---- Omitted for clarity

when I kill the ssh client on my machine the 'sleep 12345' terminates on the remote machine.

However when I'm running the exact same using Mina Java SSH client this what I see.

    SshClient client = SshClient.setUpDefaultClient();
    client.start();
    ConnectFuture connect = client.connect("user", "server", 22);

    connect.await(10000); //ms
    ClientSession session = connect.getSession();
    session.addPasswordIdentity("password");
    AuthFuture auth = session.auth();
    auth.await(10000);

    ClientChannel channel = session.createExecChannel("sleep 12345");

    OpenFuture open = channel.open();
    open.await(10000);
    Thread.sleep(15000); // ms, wait for command to run
    channel.close(true);
    session.close(true);
    client.stop();

\# ps -axf

---- Omitted for clarity

27364 ?        Ss     0:00  \\_ sshd: user@pts/0  
3277 pts/0    Ss     0:00  |   \\_ -bash
22306 pts/0    R+     0:00  |       \\_ ps axf
21699 ?        Ss     0:00  \\_ sshd: user@notty  
21796 ?        Ss     0:00      \\_ sleep 12345

---- Omitted for clarity

after code terminates the command's parent becomes the init pid:

\# ps -axf 

21796 ?        Ss     0:00 sleep 12345

\#ps -ef | grep sleep

root     21796     1  0 08:26 ?        00:00:00 sleep 12345

Is there some flag or option in Mina to cause it to terminate my command on the remote server upon closing the session?

Answer 1

ssh -t user@server sleep 12345

This allocates a PTY (pseudo-tty) for the remote session because of the "-t" option. When the ssh session disconnects, the PTY will send a SIGHUP to every process attached to the PTY. This causes the "sleep" process to exit.

To get the same behavior from a Mina session, request a PTY for the channel. I haven't worked with Mina before, but it looks like this is the way to do it:

ChannelExec channel = session.createExecChannel("sleep 12345");
channel.setUsePty(true);
// Optionally set the PTY terminal type, lines, and columns
OpenFuture open = channel.open();
...

setUsePty() and the other PTY functions are defined in PtyCapableChannelSession which is a parent class of ChannelExec.