Linux on external hdd?

Im curious as to whether or not it would be possible to run Linux from an external hard drive? The drive in question only gets turned on every once in a while as I use it for backup. I guess it applies to any os and not just Linux. So can I do this?
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Your BIOS has to support booting from USB (or FireWire?) and you are ready to go.

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Another issue is whether you will be using the external hdd to boot a specific machine or a range of different ones.  If the latter, you will need a distro that is good at boot time hardware detection, personally I would use grml for something like that (grml is a Debian/Knoppix derivative live cd with excellent hardware detection and a hard disk installer that allows you to keep the hardware detection, see ).

Duncan RoeSoftware DeveloperCommented:
Failing USB boot as an option, you can likely build a boot floppy to do the job - it needs to hold enough kernel / initrd to access the USB drive
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For linux it is no problem, like the others have said. If you were going to try it with a windows version from nt upwards (NT, wind2k, XP etc), no chance. So it won't work with all OS's...
torvaldsAuthor Commented:
Uhmmm I cant find this info anywhere. Does this option appear in all modern bios'es? I looked on asus's website and cant find the info for my board, maybe its a bit of an oddity? Asus A8N-E.
Duncan RoeSoftware DeveloperCommented:
Somewhere in the BIOS there should be a "Boot Order" menu, which typically includes floppy, HD & CD (also NET if you have PXE). If this menu includes USB, you're home.
On the A8N-E it is called 'Removable' but it means USB. :)

Just find it on the Advanced Chipset settings, and change boot order to Removable, CD-ROM, HDD
(etc., as long as Removable is first). The you'll boot from the USB hard drive whenever it is connected
at boot time. If it's not, you machine will boot normally from CD or HDD as you've specified.

Note that you can still use the HD for backups, if you connect it AFTER the computer has booted
from internal HD (provided you leave a partition that is readable by that OS).
Ie. if you have Windows on internal HD, then there has to be a FAT32 or NTFS partition on the
USB HD for Windows to see it - Windows won't see Linux native partitions. But you can have
several, just partition your HD so that you have enough space for Linux and enough for Windows backups.
..uhm, and may I ask why booting from USB HD would be problem for WinXP?
We're just going to try this next week, so I'd appreciate any pointers. :)
torvaldsAuthor Commented:
OK. Before I make the plunge and install linux again I want to ask one more question. I had linux installed before and both times when I rebooted and tried to get into windows I got an error telling me that a file was missing (cant remember the name) so then I had to reinstall windows just to get past the problem and was still left with no linux. TWICE.

So this is my last ditch attempt at linux so im wondering if it will interfere with windows at all now that its on an external drive. (the last time I put linux onto another hard drive and it still killed my windows, or windows killed itself).
Sounds like what you did was install the Linux bootloader (grub or lilo) to the MBR (Master Boot Record).  This is the last thing you want to do if you want to multi-boot with an existing Windows install, unless you know what are doing and intend to use the new bootloader to boot Windows as well.

Generally, when multibooting what you should do is install the bootloader to the partition that you've installed Linux on and then configure the Windows bootloader with a Linux entry pointing to the Linux bootloader (this is a tad oversimplified, there are Howtos on this, see ).

Since you are an external drive, you should install the bootloader to the MBR of the external drive.  Presuming you have no other removable storage or scsi devices, this would be /dev/sda on most distros I'm familiar with.
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