/**
   * 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();
    }
  }