/var/lib/tftpboot/pxelinux/pxelinux CFG/default file content is as follows:
The default vesamenu. C32
The timeout 600
Display the boot. MSG
The menu the clear
# menu background splash. PNG
The menu title Red Hat Enterprise Linux 8.1.0
The menu vshift 8
The menu rows 18
The menu margin 8
# menu hidden
The menu helpmsgrow 15
The menu tabmsgrow 13
Label linux8
Menu label ^ to Install Red Hat Enterprise Linux 8
The kernel pxelinux rh81/ called
Append the initrd= pxelinux/rh81/I nitrd. Img inst. Stage2 ks==ftp://192.168.10.10/rhel81 ftp://192.168.10.10/pub/rhel81/ks.cfg the -quiet
Label linux7
Menu label ^ to install Red Hat Enterprise Linux 7
The kernel pxelinux rh74/ called
Append the initrd= pxelinux rh74/ initrd. Img inst. Stage2 ks==ftp://192.168.10.10/rhel74 ftp://192.168.10.10/pub/rhel74/ks.cfg the -quiet
The menu end
Try a variety of methods found in called, the initrd. Img file, not a path, do not add version cannot be achieved more choice,