/**
   * Gets the value of the specified environment variable.
   *
   * @param ses SSH session.
   * @param cmd environment variable name.
   * @return environment variable value.
   * @throws JSchException In case of SSH error.
   * @throws IOException If failed.
   */
  private String exec(Session ses, String cmd) throws JSchException, IOException {
    ChannelExec ch = null;

    try {
      ch = (ChannelExec) ses.openChannel("exec");

      ch.setCommand(cmd);

      ch.connect();

      try (BufferedReader reader = new BufferedReader(new InputStreamReader(ch.getInputStream()))) {
        return reader.readLine();
      }
    } finally {
      if (ch != null && ch.isConnected()) ch.disconnect();
    }
  }
  /**
   * Executes command using {@code shell} channel.
   *
   * @param ses SSH session.
   * @param cmd Command.
   * @throws JSchException In case of SSH error.
   * @throws IOException If IO error occurs.
   * @throws IgniteInterruptedCheckedException If thread was interrupted while waiting.
   */
  private void shell(Session ses, String cmd)
      throws JSchException, IOException, IgniteInterruptedCheckedException {
    ChannelShell ch = null;

    try {
      ch = (ChannelShell) ses.openChannel("shell");

      ch.connect();

      try (PrintStream out = new PrintStream(ch.getOutputStream(), true)) {
        out.println(cmd);

        U.sleep(1000);
      }
    } finally {
      if (ch != null && ch.isConnected()) ch.disconnect();
    }
  }
  /** {@inheritDoc} */
  @Override
  public ClusterStartNodeResult call() {
    JSch ssh = new JSch();

    Session ses = null;

    try {
      if (spec.key() != null) ssh.addIdentity(spec.key().getAbsolutePath());

      ses = ssh.getSession(spec.username(), spec.host(), spec.port());

      if (spec.password() != null) ses.setPassword(spec.password());

      ses.setConfig("StrictHostKeyChecking", "no");

      ses.connect(timeout);

      boolean win = isWindows(ses);

      char separator = win ? '\\' : '/';

      spec.fixPaths(separator);

      String igniteHome = spec.igniteHome();

      if (igniteHome == null) igniteHome = win ? DFLT_IGNITE_HOME_WIN : DFLT_IGNITE_HOME_LINUX;

      String script = spec.script();

      if (script == null) script = DFLT_SCRIPT_LINUX;

      String cfg = spec.configuration();

      if (cfg == null) cfg = "";

      String startNodeCmd;
      String scriptOutputFileName =
          FILE_NAME_DATE_FORMAT.format(new Date())
              + '-'
              + UUID.randomUUID().toString().substring(0, 8)
              + ".log";

      if (win)
        throw new UnsupportedOperationException(
            "Apache Ignite cannot be auto-started on Windows from IgniteCluster.startNodes(…) API.");
      else { // Assume Unix.
        int spaceIdx = script.indexOf(' ');

        String scriptPath = spaceIdx > -1 ? script.substring(0, spaceIdx) : script;
        String scriptArgs = spaceIdx > -1 ? script.substring(spaceIdx + 1) : "";
        String rmtLogArgs = buildRemoteLogArguments(spec.username(), spec.host());
        String tmpDir = env(ses, "$TMPDIR", "/tmp/");
        String scriptOutputDir = tmpDir + "ignite-startNodes";

        shell(ses, "mkdir " + scriptOutputDir);

        // Mac os don't support ~ in double quotes. Trying get home path from remote system.
        if (igniteHome.startsWith("~")) {
          String homeDir = env(ses, "$HOME", "~");

          igniteHome = igniteHome.replaceFirst("~", homeDir);
        }

        startNodeCmd =
            new SB()
                .
                // Console output is consumed, started nodes must use Ignite file appenders for log.
                a("nohup ")
                .a("\"")
                .a(igniteHome)
                .a('/')
                .a(scriptPath)
                .a("\"")
                .a(" ")
                .a(scriptArgs)
                .a(!cfg.isEmpty() ? " \"" : "")
                .a(cfg)
                .a(!cfg.isEmpty() ? "\"" : "")
                .a(rmtLogArgs)
                .a(" > ")
                .a(scriptOutputDir)
                .a("/")
                .a(scriptOutputFileName)
                .a(" 2>& 1 &")
                .toString();
      }

      info("Starting remote node with SSH command: " + startNodeCmd, spec.logger(), log);

      shell(ses, startNodeCmd);

      return new ClusterStartNodeResultImpl(spec.host(), true, null);
    } catch (IgniteInterruptedCheckedException e) {
      return new ClusterStartNodeResultImpl(spec.host(), false, e.getMessage());
    } catch (Exception e) {
      return new ClusterStartNodeResultImpl(spec.host(), false, X.getFullStackTrace(e));
    } finally {
      if (ses != null && ses.isConnected()) ses.disconnect();
    }
  }