为什么不能在SSH(Secure Shell)登录中设置ulimit值？

CISCO 路由基础命令
Router>enable
Router# 从用户模式进入特权模式
Router#config terminal
Router(config)# 从特权模式进入全局配置模式
Router(config)#hostname teacher
teacher(config)# 为路由器配置主机名
teacher(config)#interface fastethernet 0/0
teacher(config_if)# 进入路由器的以太口配置模式
tercher(config)#banner motd $This is Aptech
company’s Router! Please don’t change the
configuration without permission! $ 配置路由器的banner信息
teacher(config)#interface fastethernet 0/0
teacher(config_if)#description This is a fast ethernet
port used to connecting the company’s intranet! 配置路由器接口的描述信息
teacher(config)#line console 0
teacher(config_line)#login
teacher(config_line)#password cisco 配置控制台密码
teacher(config)#enable password cisco 配置特权模式密码
teacher(config)#enable secret 1234 配置安全的加密密码
teacher(config)#service password-encryption 对所有密码进行加密
teacher(config)#line console 0
teacher(config_line)#exec-timeout 0 0 配置控制台会话时间
teacher(config)#line console 0
teacher(config_line)#logging synchronous 配置控制台输出日志同步
teacher(config)#interface serial 0/0
teacher(config_if)# 进入路由器的串口配置模式
teacher#show controllers serial 0/0
HD unit 0,idb=0x122c04,driver structure at 0x127098
buffer size 1524 HD unit 0，V.35 DCE ，no clock 查看路由器串口的物理状态
teacher(config)#interface serial 0/0
teacher(config_if)#clock rate 64000 设置串口的时钟频率（仅在DCE端口）
teacher(config)#interface serial 0/0
teacher(config_if)#bandwidth 64 设置串口的带宽
teacher(config)#interface serial 0/0
teacher(config_if)#no shutdown
%LINK-3-UPDOWN: Interface Seria0/0, changed state to up
%LINEPROTO-5-UPDOWN: Line Protocol on Interface Serial0/0,
changed state to up 启用路由器的串口
teacher(config)#interface serial 0/0
teacher(config_if)#shutdown
%LINK-3-UPDOWN: Interface Seria0/0, changed state to
administratively down
%LINEPROTO-5-UPDOWN: Line Protocol on Interface Serial0/0,
changed state to down 禁用路由器的串口
teacher(config)#show interface serial 0/0
serial 0/0 is up ，line protocol is up 查看Cisco 2600路由器的串口状态
可操作状态：serial 0/0 is up ，line protocol is up
连接问题：serial 0/0 is up ，line protocol is down
接口问题：serial 0/0 is down ，line protocol is down
禁用状态：serial 0/0 is administratively down ，line protocol is down
teacher(config)#interface fastethernet 0/0
teacher(config_if)#ip address 192.168.1.1 255.255.255.0 配置路由器以太口IP地址
teacher(config)#interface serial 0/0
teacher(config_if)#ip address 192.168.2.1 255.255.255.0 配置路由器串口IP地址
Router#show version
Router#show running-config
Router#show startup-config 查看路由器配置
Router#erase startup-config 删除路由器的配置