安装后，一开始有点儿无力吐槽的感觉，变化这么大？
一、Runlevel 首先一条，原来一直用的CentOS-6.5-x86_64-minimal.iso光盘镜像（400M左右无图形系统小巧便捷），而7目前最小的镜像是CentOS-7.0-1406-x86_64-livecd.iso（700M左右），默认安装后是启动图形界面，按原来的习惯要改成启动命令行，结果发现：
01.[root@localhost ~]# cat /etc/inittab02.# inittab is no longer used when using systemd.03.#04.# ADDING CONFIGURATION HERE WILL HAVE NO EFFECT ON YOUR SYSTEM.05.#06.# Ctrl-Alt-Delete is handled by /etc/systemd/system/ctrl-alt-del.target07.#08.# systemd uses ‘targets‘ instead of runlevels. By default, there are two main targets:09.#10.# multi-user.target: analogous to runlevel 311.# graphical.target: analogous to runlevel 512.#13.# To set a default target, run:14.#15.# ln -sf /lib/systemd/system/<target name>.target /etc/systemd/system/default.target16.#好吧，systemd一统天下了（它管的东西很多很多，学Centos7首先要搞定systemd）。
1.[root@localhost ~]# ls -Xl /etc/systemd/system/*.target2.lrwxrwxrwx. 1 root root 36 7月 8 23:12 /etc/systemd/system/default.target -> /lib/systemd/system/graphical.target我们来看看从前的runlevel都变成什么样了？
01.[root@localhost ~]# ls -Xl /lib/systemd/system02.[root@localhost ~]# ls -Xl /lib/systemd/system/runlevel*.target03.lrwxrwxrwx. 1 root root 15 7月 5 00:45 /lib/systemd/system/runlevel0.target -> poweroff.target04.lrwxrwxrwx. 1 root root 13 7月 5 00:45 /lib/systemd/system/runlevel1.target -> rescue.target05.lrwxrwxrwx. 1 root root 17 7月 5 00:45 /lib/systemd/system/runlevel2.target -> multi-user.target06.lrwxrwxrwx. 1 root root 17 7月 5 00:45 /lib/systemd/system/runlevel3.target -> multi-user.target07.lrwxrwxrwx. 1 root root 17 7月 5 00:45 /lib/systemd/system/runlevel4.target -> multi-user.target08.lrwxrwxrwx. 1 root root 16 7月 5 00:45 /lib/systemd/system/runlevel5.target -> graphical.target09.lrwxrwxrwx. 1 root root 13 7月 5 00:45 /lib/systemd/system/runlevel6.target -> reboot.target修改默认启动runlevel为 multi-user （貌似runlevel2 3 4 没区别了）
1.[root@localhost ~]# ln -sf /lib/systemd/system/multi-user.target /etc/systemd/system/default.target2.[root@localhost ~]# ll -X /etc/systemd/system/*.target3.lrwxrwxrwx. 1 root root 37 7月 10 09:42 /etc/systemd/system/default.target -> /lib/systemd/system/multi-user.target试试init 6 还好用不。
1.[root@localhost ~]# init 62.Connection to 192.168.150.180 closed by remote host.3.Connection to 192.168.150.180 closed.成，好用。:)
因为我从桌面版Linux 连接Centos7系统提示变成了中文，所以需要把Centos7 的root用户语言改一下，回到原汁原味。
1.[root@localhost ~]# cp .bashrc .bashrc-back2.[root@localhost ~]# echo ‘export LANG="en_Us.UTF-8"‘ >> /root/.bashrc二、Services
01.[root@localhost ~]# chkconfig02. 03.Note: This output shows SysV services only and does not include native04.systemd services. SysV configuration data might be overridden by native05.systemd configuration.06. 07.If you want to list systemd services use ‘systemctl list-unit-files‘.08.To see services enabled on particular target use09.‘systemctl list-dependencies [target]‘.10. 11.iprdump 0:off 1:off 2:on 3:on 4:on 5:on 6:off12.iprinit 0:off 1:off 2:on 3:on 4:on 5:on 6:off13.iprupdate 0:off 1:off 2:on 3:on 4:on 5:on 6:off14.livesys 0:off 1:off 2:off 3:on 4:on 5:on 6:off15.livesys-late 0:off 1:off 2:off 3:on 4:on 5:on 6:off16.netconsole 0:off 1:off 2:off 3:off 4:off 5:off 6:off17.network 0:off 1:off 2:off 3:off 4:off 5:off 6:off18.rhnsd 0:off 1:off 2:on 3:on 4:on 5:on 6:off19.vboxadd 0:off 1:off 2:on 3:on 4:on 5:on 6:off20.vboxadd-service 0:off 1:off 2:on 3:on 4:on 5:on 6:off21.vboxadd-x11 0:off 1:off 2:off 3:on 4:off 5:on 6:offSysV已经快退居二线了，想配置服务得用systemctl，先看看默认启动的服务吧。（如果不用grep过滤一下，输出结果有260多行）
01.[root@localhost ~]# systemctl list-unit-files|grep enabled02.tmp.mount enabled03.accounts-daemon.service enabled04.atd.service enabled05.auditd.service enabled06.avahi-daemon.service enabled07.bluetooth.service enabled08.chronyd.service enabled09.crond.service enabled10.dbus-org.bluez.service enabled11.dbus-org.fedoraproject.FirewallD1.service enabled12.dbus-org.freedesktop.Avahi.service enabled13.dbus-org.freedesktop.NetworkManager.service enabled14.dbus-org.freedesktop.nm-dispatcher.service enabled15.display-manager.service enabled16.dmraid-activation.service enabled17.firewalld.service enabled18.gdm.service enabled19.getty@.service enabled20.irqbalance.service enabled21.iscsi.service enabled22.kdump.service enabled23.libstoragemgmt.service enabled24.lvm2-monitor.service enabled25.mdmonitor.service enabled26.microcode.service enabled27.multipathd.service enabled28.NetworkManager-dispatcher.service enabled29.NetworkManager.service enabled30.packagekit-offline-update.service enabled31.postfix.service enabled32.rngd.service enabled33.rsyslog.service enabled34.rtkit-daemon.service enabled35.smartd.service enabled36.spice-vdagentd.service enabled37.sysstat.service enabled38.systemd-readahead-collect.service enabled39.systemd-readahead-drop.service enabled40.systemd-readahead-replay.service enabled41.tuned.service enabled42.avahi-daemon.socket enabled43.dm-event.socket enabled44.iscsid.socket enabled45.iscsiuio.socket enabled46.lvm2-lvmetad.socket enabled47.default.target enabled48.multi-user.target enabled49.remote-fs.target enabled默认居然没有启动sshd，晕！看看监听端口：
1.[root@localhost ~]# netstat -lntp2.Active Internet connections (only servers)3.Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program name 4.tcp 0 0 127.0.0.1:25 0.0.0.0:* LISTEN 2090/master果然没有22，试试老办法：
1.[root@localhost ~]# chkconfig sshd on2.Note: Forwarding request to ‘systemctl enable sshd.service‘.3.ln -s ‘/usr/lib/systemd/system/sshd.service‘ ‘/etc/systemd/system/multi-user.target.wants/sshd.service‘能用，但是指令被转发到 systemctl enable sshd.service ，以后控制服务就用这个指令了。试试：
禁用sshd：
1.[root@localhost ~]# systemctl disable sshd.service2.rm ‘/etc/systemd/system/multi-user.target.wants/sshd.service‘启用sshd:
1.[root@localhost ~]# systemctl enable sshd.service2.ln -s ‘/usr/lib/systemd/system/sshd.service‘ ‘/etc/systemd/system/multi-user.target.wants/sshd.service‘看看：
01.[root@localhost ~]# systemctl list-unit-files|grep sshd.service02.anaconda-sshd.service static 03.sshd.service enabled04. 05.[root@localhost ~]# netstat -lntp06.Active Internet connections (only servers)07.Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program name 08.tcp 0 0 127.0.0.1:25 0.0.0.0:* LISTEN 2090/master 09.tcp 0 0 0.0.0.0:22 0.0.0.0:* LISTEN 2758/sshd 10.tcp6 0 0 :::22 :::* LISTEN 2758/sshd其实启用和禁用服务就是在当前“runlevel”的配置文件目录（/etc/systemd/system/multi-user.target.wants/）里，
建立/usr/lib/systemd/system 里面对应服务配置文件的软链接；禁用服务就是删除此软链接。 有兴趣就自己看看 /usr/lib/systemd/system 里的文件，语法跟旧版/etc/init.d/ 里的服务脚本完全不同，也不能再用 /etc/init.d/sshd restart 之类的指令启动服务器了。
先试试旧方法启动服务：
1.[root@localhost ~]# service sshd start2.Redirecting to /bin/systemctl start sshd.service用新方法折腾一下：
1.[root@localhost ~]# systemctl start sshd.service2.[root@localhost ~]# systemctl stop sshd.service3.[root@localhost ~]# systemctl restart sshd.service4.[root@localhost ~]#如果没有错误，就不会输出任何信息，这个，，，，得习惯一下。
三、网络 setup工具还是保留了，但有区别，没有了网络配置，多了RHN（Centos到底是跟RedHat一家子了） [root@localhost ~]# setup
好吧，我们看看网络配置。
01.[root@localhost ~]# cat /etc/resolv.conf02.# Generated by NetworkManager03.nameserver 192.168.150.25404. 05.[root@localhost ~]# cat /etc/sysconfig/network06.# Created by anaconda07. 08.[root@localhost ~]# ll /etc/sysconfig/network-scripts/ifcfg-*09.-rw-r--r--. 1 root root 298 Jul 9 00:13 /etc/sysconfig/network-scripts/ifcfg-Auto_Ethernet10.-rw-r--r--. 1 root root 288 Jul 8 23:12 /etc/sysconfig/network-scripts/ifcfg-enp0s311.-rw-r--r--. 1 root root 254 Apr 2 23:30 /etc/sysconfig/network-scripts/ifcfg-lo12. 13.[root@localhost ~]# ifconfig14.enp0s3: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 150015.inet 192.168.150.180 netmask 255.255.255.0 broadcast 192.168.150.25516.inet6 fe80::a00:27ff:fe9a:a688 prefixlen 64 scopeid 0x20<link>17.ether 08:00:27:9a:a6:88 txqueuelen 1000 (Ethernet)18.RX packets 39317 bytes 2487945 (2.3 MiB)19.RX errors 0 dropped 0 overruns 0 frame 020.TX packets 2216 bytes 740115 (722.7 KiB)21.TX errors 0 dropped 0 overruns 0 carrier 0 collisions 022. 23.lo: flags=73<UP,LOOPBACK,RUNNING> mtu 6553624.inet 127.0.0.1 netmask 255.0.0.025.inet6 ::1 prefixlen 128 scopeid 0x10<host>26.loop txqueuelen 0 (Local Loopback)27.RX packets 6 bytes 504 (504.0 B)28.RX errors 0 dropped 0 overruns 0 frame 029.TX packets 6 bytes 504 (504.0 B)30.TX errors 0 dropped 0 overruns 0 carrier 0 collisions 031. 32.[root@localhost ~]#先改改主机名：
1.[root@localhost ~]# echo "hostname cenots7.localdomain" >>/etc/sysconfig/network2.[root@localhost ~]# reboot3.Connection to 192.168.150.180 closed by remote host.4.Connection to 192.168.150.180 closed.5.xw@Opt9010:~$ ssh root@192.168.150.1806.root@192.168.150.180‘s pass<a href="http://www.it165.net/edu/ebg/" target="_blank"class="keylink">word</a>:7.Last login: Thu Jul 10 10:01:09 20148.[root@cenots7 ~]#看看网卡配置文件：
01.[root@cenots7 ~]# cd /etc/sysconfig/network-scripts/02. 03.[root@cenots7 network-scripts]# cat ifcfg-Auto_Ethernet04.HWADDR=08:00:27:9A:A6:8805.TYPE=Ethernet06.BOOTPROTO=dhcp07.DEFROUTE=yes08.PEERDNS=yes09.PEERROUTES=yes10.IPV4_FAILURE_FATAL=no11.IPV6INIT=yes12.IPV6_AUTOCONF=yes13.IPV6_DEFROUTE=yes14.IPV6_PEERDNS=yes15.IPV6_PEERROUTES=yes16.IPV6_FAILURE_FATAL=no17.NAME="Auto Ethernet"18.UUID=76304098-8f46-4185-8337-bb7f0d90423e19.ONBOOT=yes20. 21.[root@cenots7 network-scripts]# cat ifcfg-enp0s322.HWADDR=08:00:27:9A:A6:8823.TYPE=Ethernet24.BOOTPROTO=dhcp25.DEFROUTE=yes26.PEERDNS=yes27.PEERROUTES=yes28.IPV4_FAILURE_FATAL=no29.IPV6INIT=yes30.IPV6_AUTOCONF=yes31.IPV6_DEFROUTE=yes32.IPV6_PEERDNS=yes33.IPV6_PEERROUTES=yes34.IPV6_FAILURE_FATAL=no35.NAME=enp0s336.UUID=66a635c2-9600-437b-8cfb-57e9569f68da37.ONBOOT=no看看两个文件有啥不同：
01.[root@cenots7 network-scripts]# diff ifcfg-Auto_Ethernet ifcfg-enp0s302.14,16c14,1603.< NAME="Auto Ethernet"04.< UUID=76304098-8f46-4185-8337-bb7f0d90423e05.< ONBOOT=yes06.---07.> NAME=enp0s308.> UUID=66a635c2-9600-437b-8cfb-57e9569f68da09.> ONBOOT=no两个文件MAC地址一样，ifcfg-Auto_Ethernet ONBOOT=yes，但是ifconfig结果显示的是enp0s3，有点儿费解了。
再看看我复制KVM虚拟机时经常要改的网卡MAC地址：
01.root@cenots7 network-scripts]# ll /etc/udev/rules.d/02.total 803.-rw-r--r--. 1 root root 134 Jul 9 00:47 60-vboxadd.rules04.-rw-r--r--. 1 root root 352 Jul 4 00:38 98-kexec.rules05. 06.[root@cenots7 network-scripts]# cat /etc/udev/rules.d/98-kexec.rules07.SUBSYSTEM=="cpu", ACTION=="online", PROGRAM="/bin/systemctl try-restart kdump.service"08.SUBSYSTEM=="cpu", ACTION=="offline", PROGRAM="/bin/systemctl try-restart kdump.service"09.SUBSYSTEM=="memory", ACTION=="add", PROGRAM="/bin/systemctl try-restart kdump.service"10.SUBSYSTEM=="memory", ACTION=="remove", PROGRAM="/bin/systemctl try-restart kdump.service"11. 12.[root@cenots7 network-scripts]# cat /etc/udev/rules.d/60-vboxadd.rules13.KERNEL=="vboxguest", NAME="vboxguest", OWNER="vboxadd", MODE="0660"14.KERNEL=="vboxuser", NAME="vboxuser", OWNER="vboxadd", MODE="0666"70-persistent-net.rules呢？
网卡MAC只在网卡配置文件里有，一旦变了我只需要改网卡配置文件？
1.[root@cenots7 network-scripts]# grep -r "08:00:27:9A:A6:88" /etc/2./etc/sysconfig/network-scripts/ifcfg-enp0s3:HWADDR=08:00:27:9A:A6:883./etc/sysconfig/network-scripts/ifcfg-Auto_Ethernet:HWADDR=08:00:27:9A:A6:88改一下网卡MAC 0800279AA688 -> 0800278C3746
改MAC后网卡不认了，测试结果是只需要改网卡配置文件的MAC，而且两个配置文件都要改才行。我顺便把DHCP改成了固定IP。
01.[root@cenots7 ~]# cat /etc/sysconfig/network-scripts/ifcfg-Auto_Ethernet02.HWADDR=08:00:27:8C:37:4603.# HWADDR=08:00:27:9A:A6:8804.TYPE=Ethernet05.BOOTPROTO=static06.IPADDR=192.168.150.18007.NETMASK=255.255.255.008.GATEWAY=192.168.150.25409.DEFROUTE=yes10.PEERDNS=yes11.PEERROUTES=yes12.IPV4_FAILURE_FATAL=no13.IPV6INIT=no14.IPV6_AUTOCONF=no15.IPV6_DEFROUTE=no16.IPV6_PEERDNS=no17.IPV6_PEERROUTES=no18.IPV6_FAILURE_FATAL=no19.NAME="Auto Ethernet"20.UUID=76304098-8f46-4185-8337-bb7f0d90423e21.ONBOOT=yes22. 23.[root@cenots7 ~]# cat /etc/sysconfig/network-scripts/ifcfg-enp0s324.HWADDR=08:00:27:8C:37:4625.# HWADDR=08:00:27:9A:A6:8826.TYPE=Ethernet27.BOOTPROTO=static28.IPADDR=192.168.150.18029.NETMASK=255.255.255.030.GATEWAY=192.168.150.25431.DEFROUTE=yes32.PEERDNS=yes33.PEERROUTES=yes34.IPV4_FAILURE_FATAL=no35.IPV6INIT=no36.IPV6_AUTOCONF=no37.IPV6_DEFROUTE=no38.IPV6_PEERDNS=no39.IPV6_PEERROUTES=no40.IPV6_FAILURE_FATAL=no41.NAME=enp0s342.UUID=66a635c2-9600-437b-8cfb-57e9569f68da43.ONBOOT=no好吧，这样初步解决了基础问题。回头见。。。。
原文：http://www.cnblogs.com/lonelyxmas/p/4261262.html