Ubuntu 连接时显示 There is 1 zombie process.
僵尸进程是当子进程比父进程先结束，而父进程又没有回收子进程，释放子进程占用的资源，此时子进程将成为一个僵尸进程。
Found zombie process ppid <parent_process_number>:
ps axo stat,ppid,pid,comm | grep -w defunct
Kill zombie process:
sudo kill -9 <parent_process_number>