现象
使用pexpect的ssh自动登录远程主机时，报
before (last 100 chars): 'ssh_exchange_identification: Connection closed by remote host\r\r\n'
原因
通过
who
ps aux |grep sshd
查询发现该主机上ssh连接数已经达到了最大值……
参考文章
SSH连接服务器报ssh_exchange_identification: Connection closed by remote host
