fix: Use /bin/sh as the main ssh session shell

Previously nerdlog was using the login shell via ssh (which was causing
problems with shells like `fish`), and locally it was using
`/usr/bin/env bash`, which is a bit insonsistent with the ssh conns.

Note that we can't remove the dependency on `bash` completely yet,
because the agent script still relies on bash-specific features and it's
not easy to change (e.g. I do want to use the `PIPESTATUS` and there's
no real equivalent in POSIX). But at least the main ssh session doesn't
need any bash-specific features, and using `/bin/sh` is the most
reasonable thing there.

Author: dimonomid

core/shell_transport_local.go

@@ -47,7 +47,7 @@ func (s *ShellTransportLocal) doConnect(
 
 	// Start the local shell command
 	// TODO: make it configurable; e.g. it likely won't work on Windows
-	cmd := exec.Command("/usr/bin/env", "bash")
+	cmd := exec.Command("/bin/sh")
 	stdin, err := cmd.StdinPipe()
 	if err != nil {
 		res.Err = errors.Annotatef(err, "getting stdin pipe")

core/shell_transport_ssh.go

@@ -128,7 +128,7 @@ func (st *ShellTransportSSH) doConnect(
 		return res
 	}
 
-	err = sshSession.Shell()
+	err = sshSession.Start("/bin/sh")
 	if err != nil {
 		res.Err = errors.Annotatef(err, conf.Descr)
 		return res