Failed to start LSB: Bring up/down networking 問題
1、執行 service network restart 出現以下錯誤
Restarting network (via systemctl): Job for network.service failed. See 'systemctl status network.service' and 'journalctl -xn' for details.
2、根據上面的提示，執行“systemctl status network.service”輸出以下的類似信息：
[root@localhost ~]# systemctl status network.service
network.service - LSB: Bring up/down networking
Loaded: loaded (/etc/rc.d/init.d/network)
Active: failed (Result: exit-code) since三 2014-11-05 15:30:10 CST; 1min 5s ago
11月 05 15:30:10 localhost.localdomain network[2920]: RTNETLINK answers: File exists
11月 05 15:30:10 localhost.localdomain network[2920]: RTNETLINK answers: File exists
11月 05 15:30:10 localhost.localdomain network[2920]: RTNETLINK answers: File exists
11月 05 15:30:10 localhost.localdomain network[2920]: RTNETLINK answers: File exists
11月 05 15:30:10 localhost.localdomain network[2920]: RTNETLINK answers: File exists
11月 05 15:30:10 localhost.localdomain network[2920]: RTNETLINK answers: File exists
11月 05 15:30:10 localhost.localdomain network[2920]: RTNETLINK answers: File exists
11月 05 15:30:10 localhost.localdomain systemd[1]: network.service: control process exited, code=exited status=1
11月 05 15:30:10 localhost.localdomain systemd[1]: Failed to start LSB: Bring up/down networking.
11月 05 15:30:10 localhost.localdomain systemd[1]: Unit network.service entered failed state.
3、解決的辦法（由於centos7中沒有70-persistent-net.rules這個文件，複製出來的虛擬機(vmware）需要修改mac地址），就是修改mac地址。
4、如何查看centos7複製出來的虛擬機的mac地址，需要執行 “ip addr”，輸出如下的類似信息：
[root@localhost ~]# ip addr
1: lo:
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
inet 127.0.0.1/8 scope host lo
valid_lft forever preferred_lft forever
inet6 ::1/128 scope host
valid_lft forever preferred_lft forever
2: eno16777736:
link/ether00:0f:19:10:12:f1 brd ff:ff:ff:ff:ff:ff
inet 192.168.38.135/24 brd 192.168.38.255 scope global dynamic eno16777736
valid_lft 1681sec preferred_lft 1681sec
inet6 fe80::20c:11aa:ae11:4fe4/64 scope link
valid_lft forever preferred_lft forever
注意上面加粗加紅的字，這就是新的mac地址。
接下來就剩下修改ifcfg-XXX文件了，只修改HWADDR就可以了。接下來執行service network restart就正常了。
《二》
如果還是啓動失敗 查看是否有如下錯誤信息
Nov 23 22:09:07 hdcoe02 network[597]: Bringing up loopback interface: Could not load file '/etc/sysconfig/network-scripts/ifcfg-lo'
Nov 23 22:09:07 hdcoe02 network[597]: Could not load file '/etc/sysconfig/network-scripts/ifcfg-lo'
Nov 23 22:09:08 hdcoe02 network[597]: Could not load file '/etc/sysconfig/network-scripts/ifcfg-lo'
Nov 23 22:09:08 hdcoe02 network[597]: Could not load file '/etc/sysconfig/network-scripts/ifcfg-lo' Nov 23 22:09:08 hdcoe02 network[597]: [ OK ]
Nov 23 22:09:08 hdcoe02 network[597]: Bringing up interface enp0s25: Error: Connection activation failed: Connection 'enp0s25' is not available on the device enp0s25 at this time.
設定開機啓動一個名爲NetworkManager-wait-online服務，命令爲：
systemctl enable NetworkManager-wait-online.service
《三》
我也是上面方法都測試完了 一直不成功，最後發現時因爲在VMware 虛擬機裏面的系統 右上角顯示的連接都沒有連接上，雖然報錯都一樣，最後我在虛擬機設置裏面將原來的網絡適配器刪掉，重新建了一個新的網絡適配器，這次進去，顯示連接成功，再用上面的方法，問題解決。
要瘋了！！！！今天又出現了這樣的提示；但用了上面的方法還是沒有效果，查看日誌也是找不到蛛絲馬跡，最後只能Google，
在一個博客上找到了我需要的答案，就是簡單的關閉網絡服務，然後再加載服務，然後再重啓就好了，難道Centos的一個BUG？？
[root@CT71 ~]# systemctl status network.service
● network.service - LSB: Bring up/down networking
Loaded: loaded (/etc/rc.d/init.d/network; bad; vendor preset: disabled)
Active: failed (Result: exit-code) since Fri 2017-08-04 08:20:31 CST; 1min 44s ago
Docs: man:systemd-sysv-generator(8)
Process: 62726 ExecStop=/etc/rc.d/init.d/network stop (code=exited, status=0/SUCCESS)
Process: 63183 ExecStart=/etc/rc.d/init.d/network start (code=exited, status=1/FAILURE)
Aug 04 08:20:31 CT71 network[63183]: RTNETLINK answers: File exists
Aug 04 08:20:31 CT71 network[63183]: RTNETLINK answers: File exists
Aug 04 08:20:31 CT71 network[63183]: RTNETLINK answers: File exists
Aug 04 08:20:31 CT71 network[63183]: RTNETLINK answers: File exists
Aug 04 08:20:31 CT71 network[63183]: RTNETLINK answers: File exists
Aug 04 08:20:31 CT71 network[63183]: RTNETLINK answers: File exists
Aug 04 08:20:31 CT71 systemd[1]: network.service: control process exited, code=exited status=1
Aug 04 08:20:31 CT71 systemd[1]: Failed to start LSB: Bring up/down networking.
Aug 04 08:20:31 CT71 systemd[1]: Unit network.service entered failed state.
Aug 04 08:20:31 CT71 systemd[1]: network.service failed.
如下：
systemctl stop NetworkManager
我在執行上面一步後就已經解決了問題，那個博客給出的答案還有下面的步驟，我沒有用：
systemctl disable NetworkManager
Removed symlink /etc/systemd/system/multi-user.target.wants/NetworkManager.service.
Removed symlink /etc/systemd/system/dbus-org.freedesktop.NetworkManager.service.
Removed symlink /etc/systemd/system/dbus-org.freedesktop.nm-dispatcher.service.然後重啓網絡：
systemctl start network.service
可以使用了：
[root@123 bin]# ifconfig
ens33: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 192.168.10.128 netmask 255.255.0.0 broadcast 172.17.255.255
inet6 fe80::20c:29ff:fe84:b4 prefixlen 64 scopeid 0x20<link>
ether 00:0c:29:84:00:b4 txqueuelen 1000 (Ethernet)
RX packets 3629648 bytes 315562709 (300.9 MiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 2974 bytes 295864 (288.9 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 1 (Local Loopback)
RX packets 90 bytes 6748 (6.5 KiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 90 bytes 6748 (6.5 KiB)