安裝后，一開始有點兒無力吐槽的感覺，變化這么大？
一、Runlevel
首先一條，原來一直用的CentOS-6.5-x86_64-minimal.iso光盤鏡像（400M左右無圖形系統小巧便捷），而7目前最小的鏡像是CentOS-7.0-1406-x86_64-livecd.iso（700M左右），默認安裝后是啟動圖形界面，按原來的習慣要改成啟動命令行，結果發現：
[root@localhost ~]# cat /etc/inittab # inittab is no longer used when using systemd. # # ADDING CONFIGURATION HERE WILL HAVE NO EFFECT ON YOUR SYSTEM. # # Ctrl-Alt-Delete is handled by /etc/systemd/system/ctrl-alt-del.target # # systemd uses 'targets' instead of runlevels. By default, there are two main targets: # # multi-user.target: analogous to runlevel 3 # graphical.target: analogous to runlevel 5 # # To set a default target, run: # # ln -sf /lib/systemd/system/<target name>.target /etc/systemd/system/default.target #
好吧，systemd一統天下了（它管的東西很多很多，學Centos7首先要搞定systemd）。
[root@localhost ~]# ls -Xl /etc/systemd/system/*.target lrwxrwxrwx. 1 root root 36 7月 8 23:12 /etc/systemd/system/default.target -> /lib/systemd/system/graphical.target
我們來看看從前的runlevel都變成什么樣了？
[root@localhost ~]# ls -Xl /lib/systemd/system [root@localhost ~]# ls -Xl /lib/systemd/system/runlevel*.target lrwxrwxrwx. 1 root root 15 7月 5 00:45 /lib/systemd/system/runlevel0.target -> poweroff.target lrwxrwxrwx. 1 root root 13 7月 5 00:45 /lib/systemd/system/runlevel1.target -> rescue.target lrwxrwxrwx. 1 root root 17 7月 5 00:45 /lib/systemd/system/runlevel2.target -> multi-user.target lrwxrwxrwx. 1 root root 17 7月 5 00:45 /lib/systemd/system/runlevel3.target -> multi-user.target lrwxrwxrwx. 1 root root 17 7月 5 00:45 /lib/systemd/system/runlevel4.target -> multi-user.target lrwxrwxrwx. 1 root root 16 7月 5 00:45 /lib/systemd/system/runlevel5.target -> graphical.target lrwxrwxrwx. 1 root root 13 7月 5 00:45 /lib/systemd/system/runlevel6.target -> reboot.target
修改默認啟動runlevel為 multi-user （貌似runlevel2 3 4 沒區別了）
[root@localhost ~]# ln -sf /lib/systemd/system/multi-user.target /etc/systemd/system/default.target [root@localhost ~]# ll -X /etc/systemd/system/*.target lrwxrwxrwx. 1 root root 37 7月 10 09:42 /etc/systemd/system/default.target -> /lib/systemd/system/multi-user.target
試試init 6 還好用不。
[root@localhost ~]# init 6 Connection to 192.168.150.180 closed by remote host. Connection to 192.168.150.180 closed.
成，好用。:)
因為我從桌面版Linux 連接Centos7系統提示變成了中文，所以需要把Centos7 的root用戶語言改一下，回到原汁原味。
[root@localhost ~]# cp .bashrc .bashrc-back [root@localhost ~]# echo 'export LANG="en_Us.UTF-8"' >> /root/.bashrc
二、Services
[root@localhost ~]# chkconfig Note: This output shows SysV services only and does not include native systemd services. SysV configuration data might be overridden by native systemd configuration. If you want to list systemd services use 'systemctl list-unit-files'. To see services enabled on particular target use 'systemctl list-dependencies [target]'. iprdump 0:off 1:off 2:on 3:on 4:on 5:on 6:off iprinit 0:off 1:off 2:on 3:on 4:on 5:on 6:off iprupdate 0:off 1:off 2:on 3:on 4:on 5:on 6:off livesys 0:off 1:off 2:off 3:on 4:on 5:on 6:off livesys-late 0:off 1:off 2:off 3:on 4:on 5:on 6:off netconsole 0:off 1:off 2:off 3:off 4:off 5:off 6:off network 0:off 1:off 2:off 3:off 4:off 5:off 6:off rhnsd 0:off 1:off 2:on 3:on 4:on 5:on 6:off vboxadd 0:off 1:off 2:on 3:on 4:on 5:on 6:off vboxadd-service 0:off 1:off 2:on 3:on 4:on 5:on 6:off vboxadd-x11 0:off 1:off 2:off 3:on 4:off 5:on 6:off
SysV已經快退居二線了，想配置服務得用systemctl，先看看默認啟動的服務吧。（如果不用grep過濾一下，輸出結果有260多行）
[root@localhost ~]# systemctl list-unit-files|grep enabled tmp.mount enabled accounts-daemon.service enabled atd.service enabled auditd.service enabled avahi-daemon.service enabled bluetooth.service enabled chronyd.service enabled crond.service enabled dbus-org.bluez.service enabled dbus-org.fedoraproject.FirewallD1.service enabled dbus-org.freedesktop.Avahi.service enabled dbus-org.freedesktop.NetworkManager.service enabled dbus-org.freedesktop.nm-dispatcher.service enabled display-manager.service enabled dmraid-activation.service enabled firewalld.service enabled gdm.service enabled getty@.service enabled irqbalance.service enabled iscsi.service enabled kdump.service enabled libstoragemgmt.service enabled lvm2-monitor.service enabled mdmonitor.service enabled microcode.service enabled multipathd.service enabled NetworkManager-dispatcher.service enabled NetworkManager.service enabled packagekit-offline-update.service enabled postfix.service enabled rngd.service enabled rsyslog.service enabled rtkit-daemon.service enabled smartd.service enabled spice-vdagentd.service enabled sysstat.service enabled systemd-readahead-collect.service enabled systemd-readahead-drop.service enabled systemd-readahead-replay.service enabled tuned.service enabled avahi-daemon.socket enabled dm-event.socket enabled iscsid.socket enabled iscsiuio.socket enabled lvm2-lvmetad.socket enabled default.target enabled multi-user.target enabled remote-fs.target enabled
默認居然沒有啟動sshd，暈！看看監聽端口：
[root@localhost ~]# netstat -lntp Active Internet connections (only servers) Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program name tcp 0 0 127.0.0.1:25 0.0.0.0:* LISTEN 2090/master
果然沒有22，試試老辦法：
[root@localhost ~]# chkconfig sshd on Note: Forwarding request to 'systemctl enable sshd.service'. ln -s '/usr/lib/systemd/system/sshd.service' '/etc/systemd/system/multi-user.target.wants/sshd.service'
能用，但是指令被轉發到 systemctl enable sshd.service ，以后控制服務就用這個指令了。試試：
禁用sshd：
[root@localhost ~]# systemctl disable sshd.service rm '/etc/systemd/system/multi-user.target.wants/sshd.service'
啟用sshd:
[root@localhost ~]# systemctl enable sshd.service ln -s '/usr/lib/systemd/system/sshd.service' '/etc/systemd/system/multi-user.target.wants/sshd.service'
看看：
[root@localhost ~]# systemctl list-unit-files|grep sshd.service anaconda-sshd.service static sshd.service enabled [root@localhost ~]# netstat -lntp Active Internet connections (only servers) Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program name tcp 0 0 127.0.0.1:25 0.0.0.0:* LISTEN 2090/master tcp 0 0 0.0.0.0:22 0.0.0.0:* LISTEN 2758/sshd tcp6 0 0 :::22 :::* LISTEN 2758/sshd
其實啟用和禁用服務就是在當前“runlevel”的配置文件目錄（/etc/systemd/system/multi-user.target.wants/）里，
建立/usr/lib/systemd/system 里面對應服務配置文件的軟鏈接；禁用服務就是刪除此軟鏈接。
有興趣就自己看看 /usr/lib/systemd/system 里的文件，語法跟舊版/etc/init.d/ 里的服務腳本完全不同，也不能再用 /etc/init.d/sshd restart 之類的指令啟動服務器了。
先試試舊方法啟動服務：
[root@localhost ~]# service sshd start
Redirecting to /bin/systemctl start sshd.service
用新方法折騰一下：
[root@localhost ~]# systemctl start sshd.service [root@localhost ~]# systemctl stop sshd.service [root@localhost ~]# systemctl restart sshd.service [root@localhost ~]#
如果沒有錯誤，就不會輸出任何信息，這個，，，，得習慣一下。
三、網絡
setup工具還是保留了，但有區別，沒有了網絡配置，多了RHN（Centos到底是跟RedHat一家子了）
[root@localhost ~]# setup
好吧，我們看看網絡配置。
[root@localhost ~]# cat /etc/resolv.conf # Generated by NetworkManager nameserver 192.168.150.254 [root@localhost ~]# cat /etc/sysconfig/network # Created by anaconda [root@localhost ~]# ll /etc/sysconfig/network-scripts/ifcfg-* -rw-r--r--. 1 root root 298 Jul 9 00:13 /etc/sysconfig/network-scripts/ifcfg-Auto_Ethernet -rw-r--r--. 1 root root 288 Jul 8 23:12 /etc/sysconfig/network-scripts/ifcfg-enp0s3 -rw-r--r--. 1 root root 254 Apr 2 23:30 /etc/sysconfig/network-scripts/ifcfg-lo [root@localhost ~]# ifconfig enp0s3: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500 inet 192.168.150.180 netmask 255.255.255.0 broadcast 192.168.150.255 inet6 fe80::a00:27ff:fe9a:a688 prefixlen 64 scopeid 0x20<link> ether 08:00:27:9a:a6:88 txqueuelen 1000 (Ethernet) RX packets 39317 bytes 2487945 (2.3 MiB) RX errors 0 dropped 0 overruns 0 frame 0 TX packets 2216 bytes 740115 (722.7 KiB) TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0 lo: flags=73<UP,LOOPBACK,RUNNING> mtu 65536 inet 127.0.0.1 netmask 255.0.0.0 inet6 ::1 prefixlen 128 scopeid 0x10<host> loop txqueuelen 0 (Local Loopback) RX packets 6 bytes 504 (504.0 B) RX errors 0 dropped 0 overruns 0 frame 0 TX packets 6 bytes 504 (504.0 B) TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0 [root@localhost ~]#
先改改主機名：
[root@localhost ~]# echo "hostname cenots7.localdomain" >>/etc/sysconfig/network [root@localhost ~]# reboot Connection to 192.168.150.180 closed by remote host. Connection to 192.168.150.180 closed. xw@Opt9010:~$ ssh root@192.168.150.180 root@192.168.150.180's password: Last login: Thu Jul 10 10:01:09 2014 [root@cenots7 ~]#
看看網卡配置文件：
[root@cenots7 ~]# cd /etc/sysconfig/network-scripts/ [root@cenots7 network-scripts]# cat ifcfg-Auto_Ethernet HWADDR=08:00:27:9A:A6:88 TYPE=Ethernet BOOTPROTO=dhcp DEFROUTE=yes PEERDNS=yes PEERROUTES=yes IPV4_FAILURE_FATAL=no IPV6INIT=yes IPV6_AUTOCONF=yes IPV6_DEFROUTE=yes IPV6_PEERDNS=yes IPV6_PEERROUTES=yes IPV6_FAILURE_FATAL=no NAME="Auto Ethernet" UUID=76304098-8f46-4185-8337-bb7f0d90423e ONBOOT=yes [root@cenots7 network-scripts]# cat ifcfg-enp0s3 HWADDR=08:00:27:9A:A6:88 TYPE=Ethernet BOOTPROTO=dhcp DEFROUTE=yes PEERDNS=yes PEERROUTES=yes IPV4_FAILURE_FATAL=no IPV6INIT=yes IPV6_AUTOCONF=yes IPV6_DEFROUTE=yes IPV6_PEERDNS=yes IPV6_PEERROUTES=yes IPV6_FAILURE_FATAL=no NAME=enp0s3 UUID=66a635c2-9600-437b-8cfb-57e9569f68da ONBOOT=no
看看兩個文件有啥不同：
[root@cenots7 network-scripts]# diff ifcfg-Auto_Ethernet ifcfg-enp0s3 14,16c14,16 < NAME="Auto Ethernet" < UUID=76304098-8f46-4185-8337-bb7f0d90423e < ONBOOT=yes --- > NAME=enp0s3 > UUID=66a635c2-9600-437b-8cfb-57e9569f68da > ONBOOT=no
兩個文件MAC地址一樣，ifcfg-Auto_Ethernet ONBOOT=yes，但是ifconfig結果顯示的是enp0s3，有點兒費解了。
再看看我復制KVM虛擬機時經常要改的網卡MAC地址：
root@cenots7 network-scripts]# ll /etc/udev/rules.d/ total 8 -rw-r--r--. 1 root root 134 Jul 9 00:47 60-vboxadd.rules -rw-r--r--. 1 root root 352 Jul 4 00:38 98-kexec.rules [root@cenots7 network-scripts]# cat /etc/udev/rules.d/98-kexec.rules SUBSYSTEM=="cpu", ACTION=="online", PROGRAM="/bin/systemctl try-restart kdump.service" SUBSYSTEM=="cpu", ACTION=="offline", PROGRAM="/bin/systemctl try-restart kdump.service" SUBSYSTEM=="memory", ACTION=="add", PROGRAM="/bin/systemctl try-restart kdump.service" SUBSYSTEM=="memory", ACTION=="remove", PROGRAM="/bin/systemctl try-restart kdump.service" [root@cenots7 network-scripts]# cat /etc/udev/rules.d/60-vboxadd.rules KERNEL=="vboxguest", NAME="vboxguest", OWNER="vboxadd", MODE="0660" KERNEL=="vboxuser", NAME="vboxuser", OWNER="vboxadd", MODE="0666"
70-persistent-net.rules呢？
網卡MAC只在網卡配置文件里有，一旦變了我只需要改網卡配置文件？
[root@cenots7 network-scripts]# grep -r "08:00:27:9A:A6:88" /etc/ /etc/sysconfig/network-scripts/ifcfg-enp0s3:HWADDR=08:00:27:9A:A6:88 /etc/sysconfig/network-scripts/ifcfg-Auto_Ethernet:HWADDR=08:00:27:9A:A6:88
改一下網卡MAC 0800279AA688 -> 0800278C3746
改MAC后網卡不認了，測試結果是只需要改網卡配置文件的MAC，而且兩個配置文件都要改才行。我順便把DHCP改成了固定IP。
[root@cenots7 ~]# cat /etc/sysconfig/network-scripts/ifcfg-Auto_Ethernet HWADDR=08:00:27:8C:37:46 # HWADDR=08:00:27:9A:A6:88 TYPE=Ethernet BOOTPROTO=static IPADDR=192.168.150.180 NETMASK=255.255.255.0 GATEWAY=192.168.150.254 DEFROUTE=yes PEERDNS=yes PEERROUTES=yes IPV4_FAILURE_FATAL=no IPV6INIT=no IPV6_AUTOCONF=no IPV6_DEFROUTE=no IPV6_PEERDNS=no IPV6_PEERROUTES=no IPV6_FAILURE_FATAL=no NAME="Auto Ethernet" UUID=76304098-8f46-4185-8337-bb7f0d90423e ONBOOT=yes [root@cenots7 ~]# cat /etc/sysconfig/network-scripts/ifcfg-enp0s3 HWADDR=08:00:27:8C:37:46 # HWADDR=08:00:27:9A:A6:88 TYPE=Ethernet BOOTPROTO=static IPADDR=192.168.150.180 NETMASK=255.255.255.0 GATEWAY=192.168.150.254 DEFROUTE=yes PEERDNS=yes PEERROUTES=yes IPV4_FAILURE_FATAL=no IPV6INIT=no IPV6_AUTOCONF=no IPV6_DEFROUTE=no IPV6_PEERDNS=no IPV6_PEERROUTES=no IPV6_FAILURE_FATAL=no NAME=enp0s3 UUID=66a635c2-9600-437b-8cfb-57e9569f68da ONBOOT=no
好吧，這樣初步解決了基礎問題。回頭見。。。。
參考systemd wiki：
http://zh.wikipedia.org/wiki/Systemd