1. The system environment is
[root@linux-node4 cobbler]# cat /etc/redhat-release
CentOS Linux release 7.4.1708 (Core)
2. Pit
dracut-initqueue[560]: Warning: Could not boot.
Warning: /dev/root does not exist
/sbin/dmsquash-live-root: line 273:printf: write erro: No space left do device
The reason is: the virtual machine memory allocation is insufficient.