![]() Use the image quickly for rescue then reboot. The remote rescue image's root password is sent plaintext! It's specified in the ipxe.cfg config which is pulled without encryption. To mitigate this (slightly), I setup the client systems to only do PXE boots on demand (require a keypress at boot) so that they aren't asking for remote code all the time. There are some workarounds that add some authentication bits, but in a legacy PXE boot scenario, it is essentially ripe for a hacker with physical access to the network to send remote code for execution at boot. PXE booting (by default) has NO authentication - clients just blindly accept code from the remote source and execute it. By default, the firewall on OpenWRT will allow all connections from the LAN network to TFTP and block all from the WAN. Compatibility and Security Concernsīe aware that TFTP has NO access-controls and everything in the /tftp directory will be public to everyone who can reach your TFTP server. Also this looks like a good set of iPXE and EFI instructions but I haven't tested them myself yet. More description of these options and filenames is on iPXE's website. iPXE can be built for use in UEFI cases: use snponly.efi (uses EFI's built-in SNP network stack - preferred) or ipxe.efi (has built-in network card drivers - used usually if booting from USB or CD). ![]() I've only used the legacy BIOS PXE methods. SystemRescueCD - a rescue-focused Linux distribution that comes with lots of diagnostic tools pre-installed, a command-line interface, and boot parameters that trigger a remotely-accessible SSH instance.iPXE - a very capable PXE firmware that I prefer over syslinux's PXELINUX due to its easier and more versatile configuration.HTTP - lighttpd or uhttpd, the built-in HTTP/web servers in various OpenWRT distributions.DHCP/TFTP - dnsmasq, the built-in DNS/DHCP server in OpenWRT, already has TFTP support as well!.OpenWRT - I've tested variations of this on various OpenWRT releases over the years, but this particular config I tested on 18.06.1.HTTP Server - while technically not required for PXE, HTTP is easier to use and troubleshoot than FTP.TFTP Server - newer UEFI systems can boot over HTTP, but all the old BIOS and early UEFI systems only support TFTP for downloading the bootloader.PXE Bootloader - some firmware that can download and start a Linux image.DHCP Server - that can send commands to systems to do a PXE boot. ![]() To do a PXE network boot, we need a few things: ![]() While a graphical interface (via RDP or VNC) would be nice, a command-line interface is the requirement. To be able to access a system remotely to troubleshoot when the installed operating system won't boot. Problem is that I can't easily get on site with this client so I looked to OpenWRT and a network PXE boot to try and boot Linux on the system so I could troubleshoot remotely. I suspected hard drive failure but wanted to confirm it. There was a power outage at his site and upon powering up one of their machines he was greeted with the dreaded "No bootable devices found" text error message right after the Dell splash screen. A client of mine called recently with a busted computer. ![]()
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