1、今天在一台机器上clone了5台xen虚拟机，开启至第五台是系统报以下错误
[root@localhost ~]# virsh start CentOS5.6_vm05 error: Failed to start domain CentOS5.6_vm05 error: POST operation failed: xend_post: error from xen daemon: (xend.err 'Device 768 (vbd) could not be connected. Failed to find an unused loop device')2、使用loseup命令查看发现目前使用了8个loop设备
[root@localhost ~]# losetup -a
/dev/loop0: [fd00]:543358981 (/data/vmware/CentOS/CentOS5.6_vm01.img) /dev/loop1: [fd00]:543358980 (/data/CentOS-5.6-i386-bin-DVD.iso) /dev/loop2: [fd00]:543358982 (/data/vmware/CentOS/CentOS5.6_vm02.img) /dev/loop3: [fd00]:543358980 (/data/CentOS-5.6-i386-bin-DVD.iso) /dev/loop4: [fd00]:543358980 (/data/CentOS-5.6-i386-bin-DVD.iso) /dev/loop5: [fd00]:543358984 (/data/vmware/CentOS/CentOS5.6_vm03.img) /dev/loop6: [fd00]:543358980 (/data/CentOS-5.6-i386-bin-DVD.iso) /dev/loop7: [fd00]:543358986 (/data/vmware/CentOS/CentOS5.6_vm04.img)3、系统中默认开启8个loop设备
[root@localhost ~]# ll /dev/loop*
brw-r----- 1 root disk 7, 0 Mar 8 10:36 /dev/loop0 brw-r----- 1 root disk 7, 1 Mar 8 10:36 /dev/loop1 brw-r----- 1 root disk 7, 2 Mar 8 10:36 /dev/loop2 brw-r----- 1 root disk 7, 3 Mar 8 10:36 /dev/loop3 brw-r----- 1 root disk 7, 4 Mar 8 10:36 /dev/loop4 brw-r----- 1 root disk 7, 5 Mar 8 10:36 /dev/loop5 brw-r----- 1 root disk 7, 6 Mar 8 10:36 /dev/loop6 brw-r----- 1 root disk 7, 7 Mar 8 10:36 /dev/loop74、编辑/etc/modprobe.conf 文件按需求增加loop设备数量
[root@localhost ~]# echo "options loop max_loop=64" >> /etc/modprobe.conf
5、重新加载loop模块
[root@localhost ~]# rmmod loop
ERROR: Module loop is in use直接卸载时提示loop模块正在使用，所以要先把GuestOS停掉才行
[root@localhost ~]# virsh shutdown CentOS5.6_vm01
Domain CentOS5.6_vm01 is being shutdown[root@localhost ~]# virsh shutdown CentOS5.6_vm02
Domain CentOS5.6_vm02 is being shutdown[root@localhost ~]# virsh shutdown CentOS5.6_vm03
Domain CentOS5.6_vm03 is being shutdown[root@localhost ~]# virsh shutdown CentOS5.6_vm04
Domain CentOS5.6_vm04 is being shutdown[root@localhost ~]# losetup -a
[root@localhost ~]# rmmod loop [root@localhost ~]# modprobe loop [root@localhost ~]# ll /dev/loop*发现已经有64个loop设备可以使用了（太多了，就不往上贴了）
至此开启多台GuestOS提示无loop设备可用问题解决完毕！：）