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I have Linux Mint installed on an external hard drive, and I have the 4 main partitions (/boot, swap, /, and /home). I also have 600GB of unallocated space. I know there's always the chance of data loss, but would it be any more dangerous to add a partition while booted to that physical disk than it would while booted to another? Would adding a partition while booted to that disk be like erasing / as root?

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3 Answers 3

up vote 2 down vote accepted

Since "when booted" means that the OS that needs to make changes and write to the disk, is also running from the same disk, has a higher potential for problems/disaster if something goes wrong.

Following Murphy's Law, "Anything that can go wrong, will", you are safest to run the operation isolated from the operating system.

My suggestion would be to use the system boot disk (install), or a generic "Live CD".

And for what it is worth, I have partitioned and formatted partitions in the same manner you are describing without ever having an issue, only the flip side I could have been incredibly lucky all those times.

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Lawl, thanks for fixing that. Ohm's do not really apply here! –  Tim Jul 2 '12 at 19:21
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Gparted also has a live CD version. It's quite safe if you're careful. It'll warn if you try to damage/alter mounted partitions. –  Alexios Jul 2 '12 at 20:35
    
@Alexios that's a great option, thanks! –  Tim Jul 3 '12 at 12:58

It's perfectly safe to convert your unallocated space to a partition while your system is running. The only practical danger is in human error (i.e., yours) or a power loss while the partition table is being written. These just as likely to happen while booted normally as they are booted from a Live CD.

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And GParted is pretty good at sanity checks. –  Alexios Jul 2 '12 at 20:35

It is safe to modify any partition table while booted under Linux.

If the modification alters any partitions which are currently in use, then the kernel will simply ignore the new partition table until the next boot.

(Edit: Disregard this, it is incorrect- see comment below!)

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That's not quite true. For example, if you shrink a partition that's in use and enlarge another partition to use the space and create a filesystem on the enlarged partition, the kernel will willingly mount that new filesystem and trash the data in the still-mounted shrunk partition. It's ok to start using formerly-unused space, and to keep using space that you've unallocated, but mixing the two is calling for trouble. –  Gilles Jul 2 '12 at 22:02

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