[root@kvm-01 ~]# virt-install --virt-type kvm --os-type=linux --os-variant rhel7 --name centos7-test --memory 1024 --vcpus 1 --disk /opt/centos7-test.raw,format=raw,size=10 --cdrom /opt/CentOS-7-x86_64-Minimal-1810.iso --network network=default --graphics vnc,listen=0.0.0.0 --noautoconsole
Starting install...
Allocating 'centos2.raw' | 10 GB 00:00:00
Domain installation still in progress. You can reconnect to
the console to complete the installation process.
# --virt-type kvm ：虚拟化类型kvm、qemu
# --os-type=linux ：系统类型
# --os-variant rhel7 ：系统版本
# --name centos7-test ：虚拟机名称（唯一）
# --memory 1024 ：虚拟机内存
# --vcpus 1 ：CPU核数
# --disk /opt/centos2.raw,format=raw,size=10 ：硬盘位置、格式、容量（唯一）
# --cdrom /opt/CentOS-7-x86_64-Minimal-1810.iso ：使用的镜像文件
# --network network=default ：默认网络
# --graphics vnc,listen=0.0.0.0 ：vnc显示输出
# --noautoconsole
[root@kvm-01 ~]# virsh list --all
Id Name State
----------------------------------------------------
1 centos7-test running
【3】kvm常用管理命令
# 查看运行中的虚拟机
[root@kvm-01 ~]# virsh list
Id Name State
----------------------------------------------------
# 查看所有存在的虚拟机
[root@kvm-01 ~]# virsh list --all
Id Name State
----------------------------------------------------
- centos7-test shut off
# 启动虚拟机
[root@kvm-01 ~]# virsh start centos7-test
Domain centos7-test started
[root@kvm-01 ~]# virsh list
Id Name State
----------------------------------------------------
2 centos7-test running
# 关机虚拟机
[root@kvm-01 ~]# virsh shutdown centos7-test
Domain centos7-test is being shutdown
# 拔电源关机
[root@kvm-01 ~]# virsh destroy centos7-test
# 重启
[root@kvm-01 ~]# virsh reboot centos7-test
# 磁盘文件占用空间，创建的时候分配了10G，查看目前已使用
[root@kvm-01 ~]# du -smh /opt/*
1.4G /opt/centos2.raw
918M /opt/CentOS-7-x86_64-Minimal-1810.iso
# 磁盘空间分配的大小
[root@kvm-01 ~]# ll -h /opt/
total 2.3G
-rw------- 1 qemu qemu 10G Jul 14 00:44 centos2.raw
-rw-r--r-- 1 qemu qemu 918M Jul 13 08:42 CentOS-7-x86_64-Minimal-1810.iso
# 备份磁盘文件
[root@kvm-01 ~]# cp /opt/centos2.raw /backup/
# 配置文件备份
[root@kvm-01 ~]# virsh dumpxml centos7-test > kvm_centos7-test.xml
# 删除虚拟机，先关机在删除，删除后磁盘文件是不会被删除的注意
[root@kvm-01 ~]# virsh list --all
Id Name State
----------------------------------------------------
1 centos7-test running
[root@kvm-01 ~]# virsh shutdown centos7-test
Domain centos7-test is being shutdown
[root@kvm-01 ~]# virsh undefine centos7-test
Domain centos7-test has been undefined
[root@kvm-01 ~]# virsh list --all
Id Name State
----------------------------------------------------
# 上面备份的配置文件，根据配置文件导入虚拟机
[root@kvm-01 ~]# ls
anaconda-ks.cfg kvm_centos7-test.xml
[root@kvm-01 ~]# virsh define kvm_centos7-test.xml
Domain centos7-test defined from kvm_centos7-test.xml
[root@kvm-01 ~]# virsh list --all
Id Name State
----------------------------------------------------
- centos7-test shut off
# 修改配置文件edit,如果修改了磁盘文件的名称，但是没有修改配置文件，启动虚拟机时他会找不到磁盘文件而报错
[root@kvm-01 ~]# virsh edit centos7-test
[root@kvm-01 opt]# mv centos7-test.raw centos7-test-7-14.raw
[root@kvm-01 opt]# virsh start centos7-test
error: Failed to start domain centos7-test
error: Cannot access storage file '/opt/centos7-test.raw': No such file or directory
[root@kvm-01 opt]# virsh edit centos7-test
[root@kvm-01 opt]# virsh start centos7-test
Domain centos7-test started
# 修改cpu的核数，很多时候修改了配置需要重启生效，reboot不管用
[root@kvm-01 opt]# virsh edit centos7-test
2
[root@kvm-01 opt]# virsh shutdown centos7-test
Domain centos7-test is being shutdown
[root@kvm-01 opt]# virsh start centos7-test
Domain centos7-test started
# 重命名，不能处于运行期间修改
[root@kvm-01 opt]# virsh shutdown centos7-test
Domain centos7-test is being shutdown
[root@kvm-01 opt]# virsh domrename centos7-test centos7-test-7-14
Domain successfully renamed
[root@kvm-01 opt]# virsh list --all
Id Name State
----------------------------------------------------
- centos7-test-7-14 shut off
[root@kvm-01 opt]# virsh start centos7-test-7-14
Domain centos7-test-7-14 started
# 挂起处于运行的虚拟机
[root@kvm-01 opt]# virsh suspend centos7-test-7-14
Domain centos7-test-7-14 suspended
[root@kvm-01 opt]# virsh list --all
Id Name State
----------------------------------------------------
8 centos7-test-7-14 paused
# 恢复被挂起的虚拟机，恢复后虚拟机的时间可能会落后
[root@kvm-01 opt]# virsh resume centos7-test-7-14
Domain centos7-test-7-14 resumed
[root@kvm-01 opt]# virsh list --all
Id Name State
----------------------------------------------------
8 centos7-test-7-14 running
# 建议虚拟机下载时间同步服务
[root@localhost ~]# yum -y instarll chrony
# 查询vnc端口号
[root@kvm-01 opt]# virsh vncdisplay centos7-test-7-14
:0
# 一个虚拟机相当于一个qemu进程
[root@kvm-01 opt]# ps -ef | grep qemu
# KVM 宿主机开机自动启动虚拟机，宿主机开机时只要启动了libvirtd服务，就会拉起虚拟机
[root@kvm-01 opt]# virsh autostart centos7-test-7-14
Domain centos7-test-7-14 marked as autostarted
[root@kvm-01 opt]# virsh list --all
Id Name State
----------------------------------------------------
- centos7-test-7-14 shut off
[root@kvm-01 opt]# systemctl restart libvirtd.service
[root@kvm-01 opt]# virsh list --all
Id Name State
----------------------------------------------------
1 centos7-test-7-14 running
# 查看虚拟机是否被设置开机自启，如果我们删除了autostart目录下的软连接就相当与关闭了开机自启
[root@kvm-01 opt]# ll -h /etc/libvirt/qemu/autostart/
total 0
lrwxrwxrwx 1 root root 39 Jul 14 02:14 centos7-test-7-14.xml -> /etc/libvirt/qemu/centos7-test-7-14.xml
[root@kvm-01 opt]# rm -rf /etc/libvirt/qemu/autostart/centos7-test-7-14.xml
[root@kvm-01 opt]# virsh shutdown centos7-test-7-14
Domain centos7-test-7-14 is being shutdown
[root@kvm-01 opt]# virsh list --all
Id Name State
----------------------------------------------------
- centos7-test-7-14 shut off
[root@kvm-01 opt]# systemctl restart libvirtd.service
[root@kvm-01 opt]# virsh list --all
Id Name State
----------------------------------------------------
- centos7-test-7-14 shut off
[root@kvm-01 opt]# ln -s /etc/libvirt/qemu/centos7-test-7-14.xml /etc/libvirt/qemu/autostart/
[root@kvm-01 opt]# ll /etc/libvirt/qemu/autostart/
total 0
lrwxrwxrwx 1 root root 39 Jul 14 02:23 centos7-test-7-14.xml -> /etc/libvirt/qemu/centos7-test-7-14.xml
[root@kvm-01 opt]# systemctl restart libvirtd.service
[root@kvm-01 opt]# virsh list --all
Id Name State
----------------------------------------------------
1 centos7-test-7-14 running
# 第二种方式查看虚拟机是否被设置开机自启
[root@kvm-01 opt]# virsh list --autostart --all
Id Name State
----------------------------------------------------
1 centos7-test-7-14 running
# 取消开机自启、1：删除软连接 2：命令方式
[root@kvm-01 opt]# virsh autostart --disable centos7-test-7-14
Domain centos7-test-7-14 unmarked as autostarted
[root@kvm-01 opt]# virsh list --autostart --all
Id Name State
----------------------------------------------------
【4】console控制台登录
console：命令版的控制台
vnc：图形版的控制台
# 7系统的方式，在虚拟机中配置
[root@kvm-01 opt]# ssh [email protected][email protected]'s password:
Last login: Fri Jul 14 13:57:14 2023 from gateway
[root@localhost ~]# grubby --update-kernel=ALL --args="console=ttyS0,115200n8"
[root@localhost ~]# reboot
Connection to 192.168.122.75 closed by remote host.
Connection to 192.168.122.75 closed.
[root@kvm-01 opt]#
[root@kvm-01 opt]# virsh list --all
Id Name State
----------------------------------------------------
1 centos7-test-7-14 running
[root@kvm-01 opt]# virsh console centos7-test-7-14
Connected to domain centos7-test-7-14
Escape character is ^]
ctrl+] 退出 、回车进入
CentOS Linux 7 (Core)
Kernel 3.10.0-957.el7.x86_64 on an x86_64
localhost login: root
Password:
Last login: Fri Jul 14 14:33:14 from gateway
[root@localhost ~]#
[root@localhost ~]# ctrl + ] 退出 ，返回到宿主机界面
[root@kvm-01 opt]#
qcow2：copy on write （写时复制）占用空间小，支持快照功能，性能比raw差一点，方便传输，总50G，但是我们使用了1G，传输到新机器时只传输1G
# 创建一台磁盘为qcow2格式的虚拟机
[root@kvm-01 opt]# virt-install --virt-type kvm --os-type=linux --os-variant rhel7 --name centos7-test-qcow2 --memory 1024 --vcpus 1 --disk /opt/centos7-test-qcow2.qcow2,format=qcow2,size=10 --cdrom /opt/CentOS-7-x86_64-Minimal-1810.iso --network network=default --graphics vnc,listen=0.0.0.0 --noautoconsole
Starting install...
Allocating 'centos7-test-qcow2.qcow2' | 10 GB 00:00:00
Domain installation still in progress. You can reconnect to
the console to complete the installation process.
【7】将raw格式的磁盘挂载到宿主机
# raw 可以直接挂载到宿主机，先关机,查询磁盘的位置偏移量
[root@kvm-01 opt]# virsh shutdown centos7-test-7-14
Domain centos7-test-7-14 is being shutdown
[root@kvm-01 opt]# fdisk /opt/centos7-test-7-14.raw
Welcome to fdisk (util-linux 2.23.2).
Changes will remain in memory only, until you decide to write them.
Be careful before using the write command.
Command (m for help): p
Disk /opt/centos7-test-7-14.raw: 10.7 GB, 10737418240 bytes, 20971520 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk label type: dos
Disk identifier: 0x000b436c
Device Boot Start End Blocks Id System
/opt/centos7-test-7-14.raw1 * 2048 20971519 10484736 83 Linux
Command (m for help): q
[root@kvm-01 opt]# echo $((2048*512))
1048576
[root@kvm-01 opt]# mkdir /images
[root@kvm-01 opt]# mount -o loop,offset=1048576 /opt/centos7-test-7-14.raw /images/
[root@kvm-01 opt]# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/cl-root 17G 5.1G 12G 30% /
devtmpfs 1.9G 0 1.9G 0% /dev
tmpfs 1.9G 0 1.9G 0% /dev/shm
tmpfs 1.9G 8.7M 1.9G 1% /run
tmpfs 1.9G 0 1.9G 0% /sys/fs/cgroup
/dev/sda1 1014M 139M 876M 14% /boot
tmpfs 378M 0 378M 0% /run/user/0
/dev/loop0 10G 1.3G 8.8G 13% /images
[root@kvm-01 opt]# ls /images/
bin dev home lib64 mnt proc run srv tmp var
boot etc lib media opt root sbin sys usr
[root@kvm-01 opt]# du -smh /images/
1.2G /images/
# 挂载之后我们可以管理文件，创建文件，或者直接修改虚拟机的密码
# 修改密码方式一
[root@kvm-01 opt]# chroot /images/
[root@kvm-01 /]# passwd
Changing password for user root.
New password:
BAD PASSWORD: The password is a palindrome
Retype new password:
passwd: all authentication tokens updated successfully.
[root@kvm-01 /]# exit
exit
[root@kvm-01 opt]# umount /images
[root@kvm-01 opt]# virsh start centos7-test-7-14
Domain centos7-test-7-14 started
[root@kvm-01 opt]# ssh [email protected][email protected]'s password:
Last login: Fri Jul 14 14:57:42 2023 from gateway
# 修改密码方式二
[root@kvm-01 opt]# virsh shutdown centos7-test-7-14
Domain centos7-test-7-14 is being shutdown
[root@kvm-01 opt]# mount -o loop,offset=1048576 /opt/centos7-test-7-14.raw /images/
[root@kvm-01 opt]# ls /images/
bin dev home lib64 mnt proc run srv tmp var
boot etc lib media opt root sbin sys usr
[root@kvm-01 ~]# chroot /images/
[root@kvm-01 /]# echo 123|passwd --stdin root
Changing password for user root.
passwd: all authentication tokens updated successfully.
[root@kvm-01 /]# exit
exit
[root@kvm-01 ~]# umount /images
[root@kvm-01 ~]# virsh start centos7-test-7-14
Domain centos7-test-7-14 started
[root@kvm-01 ~]# ssh [email protected][email protected]'s password:
Last login: Fri Jul 14 15:29:35 2023 from gateway
【8】磁盘的管理命令
# 查看磁盘真实使用情况 info
[root@kvm-01 ~]# qemu-img info /opt/centos7-test-7-14.raw
image: /opt/centos7-test-7-14.raw
file format: raw
virtual size: 10G (10737418240 bytes)
disk size: 1.3G
# 创建一块 qcow2 的 磁盘
[root@kvm-01 ~]# qemu-img create -f qcow2 /opt/test-qcow2 1G
Formatting '/opt/test-qcow2', fmt=qcow2 size=1073741824 encryption=off cluster_size=65536 lazy_refcounts=off
[root@kvm-01 ~]# ls /opt/
centos7-test-7-14.raw CentOS-7-x86_64-Minimal-1810.iso
centos7-test-qcow2.qcow2 test-qcow2
[root@kvm-01 ~]# qemu-img info /opt/test-qcow2
image: /opt/test-qcow2
file format: qcow2
virtual size: 1.0G (1073741824 bytes)
disk size: 196K
cluster_size: 65536
Format specific information:
compat: 1.1
lazy refcounts: false
# 创建一块 raw 的 磁盘
[root@kvm-01 ~]# qemu-img create -f raw /opt/test-raw 1G
Formatting '/opt/test-raw', fmt=raw size=1073741824
[root@kvm-01 ~]# qemu-img info /opt/test-raw
image: /opt/test-raw
file format: raw
virtual size: 1.0G (1073741824 bytes)
disk size: 0
# qcow2 磁盘扩容
[root@kvm-01 ~]# qemu-img resize /opt/test-qcow2 +2G
Image resized.
[root@kvm-01 ~]# qemu-img info /opt/test-qcow2
image: /opt/test-qcow2
file format: qcow2
virtual size: 3.0G (3221225472 bytes)
disk size: 260K
cluster_size: 65536
Format specific information:
compat: 1.1
lazy refcounts: false
[root@kvm-01 ~]# qemu-img resize /opt/test-qcow2 10G
Image resized.
[root@kvm-01 ~]# qemu-img info /opt/test-qcow2
image: /opt/test-qcow2
file format: qcow2
virtual size: 10G (10737418240 bytes)
disk size: 200K
cluster_size: 65536
Format specific information:
compat: 1.1
lazy refcounts: false
# raw 磁盘扩容
[root@kvm-01 ~]# qemu-img resize /opt/test-raw 10G
Image resized.
[root@kvm-01 ~]# qemu-img info /opt/test-raw
image: /opt/test-raw
file format: raw
virtual size: 10G (10737418240 bytes)
disk size: 0
# convert 转换磁盘格式，将raw格式转为为qcow2格式，先关闭虚拟机
[root@kvm-01 ~]# virsh list --all
Id Name State
----------------------------------------------------
4 centos7-test-7-14 running
- centos7-test-qcow2 shut off
[root@kvm-01 ~]# virsh shutdown centos7-test-7-14
Domain centos7-test-7-14 is being shutdown
[root@kvm-01 ~]# virsh list --all
Id Name State
----------------------------------------------------
- centos7-test-7-14 shut off
- centos7-test-qcow2 shut off
[root@kvm-01 ~]# time qemu-img convert -f raw -O qcow2 /opt/centos7-test-7-14.raw /opt/centos7-test-7-14.raw-qcow2
real 0m12.599s
user 0m0.064s
sys 0m1.897s
# 如果想使用转为后的磁盘，修改虚拟机配置文件
[root@kvm-01 ~]# virsh edit centos7-test-7-14
[root@kvm-01 ~]# virsh start centos7-test-7-14
Domain centos7-test-7-14 started
[root@kvm-01 ~]# ll -h /opt/
total 4.9G
-rw------- 1 root root 10G Jul 14 04:02 centos7-test-7-14.raw
-rw-r--r-- 1 qemu qemu 1.4G Jul 14 04:09 centos7-test-7-14.raw-qcow2
[root@kvm-01 ~]# virsh dumpxml centos7-test-7-14 | grep qcow2
【9】创建快照-内部快照
raw格式不支持快照
创建的快照都在磁盘文件中，属于内部快照
[root@kvm-01 ~]# virsh snapshot-create centos7-test-7-14
Domain snapshot 1689322674 created
[root@kvm-01 ~]# qemu-img info /opt/centos7-test-7-14.raw-qcow2
image: /opt/centos7-test-7-14.raw-qcow2
file format: qcow2
virtual size: 10G (10737418240 bytes)
disk size: 3.3G
cluster_size: 65536
Snapshot list:
ID TAG VM SIZE DATE VM CLOCK
1 1689322674 222M 2023-07-14 04:17:54 00:09:03.995
Format specific information:
compat: 1.1
lazy refcounts: false
【10】查看虚拟机中的快照
[root@kvm-01 ~]# virsh snapshot-list centos7-test-7-14
Name Creation Time State
------------------------------------------------------------
1689322674 2023-07-14 04:17:54 -0400 running
【11】创建快照并起名称
[root@kvm-01 ~]# virsh snapshot-create-as centos7-test-7-14 --name initialize
Domain snapshot initialize created
[root@kvm-01 ~]# virsh snapshot-list centos7-test-7-14
Name Creation Time State
------------------------------------------------------------
1689322674 2023-07-14 04:17:54 -0400 running
initialize 2023-07-14 04:26:37 -0400 running
【12】删除快照
[root@kvm-01 ~]# virsh snapshot-delete centos7-test-7-14 --snapshotname initialize
Domain snapshot initialize deleted
[root@kvm-01 ~]# virsh snapshot-list centos7-test-7-14
Name Creation Time State
------------------------------------------------------------
1689322674 2023-07-14 04:17:54 -0400 running
【13】还原快照
[root@kvm-01 ~]# virsh console centos7-test-7-14
Connected to domain centos7-test-7-14
Escape character is ^]
[root@localhost ~]# ls /tmp/
ks-script-GjIS1d
systemd-private-ac9445ab0ec04d66b6b67d4c2828d3f6-chronyd.service-ZFYI3F
yum.log
[root@localhost ~]# rm -rf /tmp/*
[root@kvm-01 ~]# virsh snapshot-revert centos7-test-7-14 --snapshotname 1689322674
[root@kvm-01 ~]# virsh console centos7-test-7-14
Connected to domain centos7-test-7-14
Escape character is ^]
[root@localhost ~]# ls /tmp/
ks-script-GjIS1d
systemd-private-ac9445ab0ec04d66b6b67d4c2828d3f6-chronyd.service-ZFYI3F
yum.log
[root@kvm-01 ~]# virt-install --virt-type kvm --os-type=linux --os-variant rhel7 --name centos7-bridge-qcow2 --memory 1024 --vcpus 1 --disk /opt/centos7-bridge-qcow2,format=qcow2,size=10 --cdrom /opt/CentOS-7-x86_64-Minimal-1810.iso --network bridge=br0 --graphics vnc,listen=0.0.0.0 --noautoconsole
Starting install...
Allocating 'centos7-bridge-qcow2' | 10 GB 00:00:00
Domain installation still in progress. You can reconnect to
the console to complete the installation process.
【21】将现有的虚拟机更改为桥接模式
先将虚拟机关机
[root@kvm-01 ~]# virsh shutdown centos7-test-7-14
Domain centos7-test-7-14 is being shutdown
[root@kvm-01 ~]# virsh edit centos7-test-7-14
# 启动测试、验证
[root@kvm-01 ~]# virsh start centos7-test-7-14
Domain centos7-test-7-14 started
[root@kvm-01 ~]# virsh console centos7-test-7-14
Connected to domain centos7-test-7-14
Escape character is ^]
CentOS Linux 7 (Core)
Kernel 3.10.0-957.el7.x86_64 on an x86_64
localhost login: root
Password:
Last login: Fri Jul 14 19:25:30 on ttyS0
[root@localhost ~]# ip a
## 调整最大内存值，先关机
[root@kvm-01 ~]# virsh shutdown centos7-test-7-14
Domain centos7-test-7-14 is being shutdown
[root@kvm-01 ~]# virsh list --all
Id Name State
----------------------------------------------------
- centos7-bridge-qcow2 shut off
- centos7-test-7-14 shut off
[root@kvm-01 ~]# virsh setmaxmem centos7-test-7-14 2048M
[root@kvm-01 ~]# virsh start centos7-test-7-14
Domain centos7-test-7-14 started
[root@kvm-01 ~]# virsh list --all
Id Name State
----------------------------------------------------
1 centos7-test-7-14 running
- centos7-bridge-qcow2 shut off
# 远程连接查看其他宿主机有多少虚拟机
[root@kvm-01 ~]# virsh -c qemu+ssh://[email protected]/system list
[email protected]'s password:
Id Name State
----------------------------------------------------
# 迁移正在运行的虚拟机
[root@kvm-01 ~]# virsh migrate centos7-test-7-14 qemu+ssh://[email protected]/system
[email protected]'s password:
error: Unsafe migration: Migration may lead to data corruption if disks use cache != none or cache != directsync
[root@kvm-01 ~]# virsh migrate centos7-test-7-14 qemu+ssh://[email protected]/system --unsafe
[email protected]'s password:
[root@kvm-01 ~]# virsh -c qemu+ssh://[email protected]/system list
[email protected]'s password:
Id Name State
----------------------------------------------------
2 centos7-test-7-14 running
# 注意，这样只是将进程迁移过去了，并没有迁移配置文件，虚拟机关闭后会消失，不是永久迁移，使用以下
[root@kvm-01 ~]# virsh migrate centos7-test-7-14 qemu+ssh://[email protected]/system --unsafe --verbose --persistent --undefinesource
[email protected]'s password:
Migration: [100 %]
[root@kvm-01 ~]# virsh list --all
Id Name State
----------------------------------------------------
- centos7-bridge-qcow2 shut off
# 我们发现本地就没有centos7-test-7-14了，被迁移到了10.0.0.32中，永久
[root@kvm-01 ~]# virsh -c qemu+ssh://[email protected]/system list
[email protected]'s password:
Id Name State
----------------------------------------------------
3 centos7-test-7-14 running
[root@kvm-02 ~]# virsh destroy centos7-test-7-14
Domain centos7-test-7-14 destroyed
[root@kvm-02 ~]# virsh list --all
Id Name State
----------------------------------------------------
- centos7-test-7-14 shut off
利用JavaScript进行对象排序，根据用户的年龄排序展示
<script>
var bob={
name;bob,
age:30
}
var peter={
name;peter,
age:30
}
var amy={
name;amy,
age:24
}
var mike={
name;mike,
age:29
}
var john={
FLP
One famous theory in distributed computing, known as FLP after the authors Fischer, Lynch, and Patterson, proved that in a distributed system with asynchronous communication and process crashes,
每一行命令都是用分号(;)作为结束
对于MySQL，第一件你必须牢记的是它的每一行命令都是用分号(;)作为结束的，但当一行MySQL被插入在PHP代码中时，最好把后面的分号省略掉，例如：
mysql_query("INSERT INTO tablename(first_name,last_name)VALUES('$first_name',$last_name')");
题目链接：zoj 3820 Building Fire Stations
题目大意：给定一棵树，选取两个建立加油站，问说所有点距离加油站距离的最大值的最小值是多少，并且任意输出一种建立加油站的方式。
解题思路：二分距离判断，判断函数的复杂度是o(n)，这样的复杂度应该是o(nlogn)，即使常数系数偏大，但是居然跑了4.5s，也是醉了。 判断函数里面做了3次bfs，但是每次bfs节点最多
