问题解决：Centos7挂起重开无IP的问题，不必每次都重新设置network
使用vim修改配置文件
vim /etc/sysconfig/network-scripts/ifcfg-ens33
将最下方的ONBOOT=no改为yes
保存退出
再输入service network restart 再重启网络就解决了
实验一：修改centos7的网卡名称
1）终端下输入命令gedit /boot/grub2/grub.cfg进入图形编辑界面
linux16 后加 net.ifnames=0
最后
reboot重启一下就可以了2）使用vim命令修改
最后
reboot重启
实验二：时间同步
ntpdate 172.16.0.1
nano /etc/ntp.conf
server 172.16.0.1 iburst
service ntpd start centos6
systemctl start ntpd centos7
实验三：screen——建立会话
一个主机，两个终端
lsblk
rpm -ivh /run/media/root/CentOS\ 7\ x86_64/Packages/screen-4.1.0-0.23.20120314git3c2946.el7_2.x86_64.rpm
A: screen -S help
B: screen -ls
screen -x help
exit
实验四：更改Centos 6开机运行级别为命令行界面
vim /etc/inittab
# inittab is only used by upstart for the default runlevel.
#
# ADDING OTHER CONFIGURATION HERE WILL HAVE NO EFFECT ON YOUR SYSTEM.
#
# System initialization is started by /etc/init/rcS.conf
#
# Individual runlevels are started by /etc/init/rc.conf
#
# Ctrl-Alt-Delete is handled by /etc/init/control-alt-delete.conf
#
# Terminal gettys are handled by /etc/init/tty.conf and /etc/init/serial.conf,
# with configuration in /etc/sysconfig/init.
#
# For information on how to write upstart event handlers, or how
# upstart works, see init(5), init(8), and initctl(8).
#
# Default runlevel. The runlevels used are:
# 0 - halt (Do NOT set initdefault to this)
# 1 - Single user mode
# 2 - Multiuser, without NFS (The same as 3, if you do not have networking)
# 3 - Full multiuser mode
# 4 - unused
# 5 - X11
# 6 - reboot (Do NOT set initdefault to this)
#
id:5:initdefault: #将此处的数字改为3即可
"/etc/inittab" 26L, 884C
点击i ,编辑vim文件，然后Esc键退出编辑 ，冒号：+ w键写入 、再冒号：+ q键退出
实验五：更改Centos7下的运行级别
systemctl isolate multi-user.target
systemctl isolate runlevel3.target //作用与上面相同
或者
systemctl isolate graphical.target
systemctl isolate runlevel5.target //作用与上面相同
上面的的命令是暂时的更改，要想开机后默认运行命令行界面：
第一步：rm /etc/systemd/system/default.target //删除默认的开机运行文件
第二步：
1 ln -sf /lib/systemd/system/multi-user.target /etc/systemd/system/default.target
2 ln -sf /lib/systemd/system/runlevel3.target /etc/systemd/system/default.target
3 sytemctl set-default multi-user.target
上面3个命令任选其一即可。
