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If an external hard drive has been formatted from a certain linux-pc with ext4 file system could it be open on other, different linux-pc or it can be open just on the pc on which it was been formatted?

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    An ext4 filesystem can be opened on any computer that can understand the filesystem. There is no encryption or other mechanism to tie it to a particular machine. You might like to clarify your question with the issue you're seeing. – roaima Aug 1 at 17:42
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    ^^ Correction. There is usually no encryption used on ext4 filesystems. But see this page on the Gentoo Wiki for a description of using its file-based encryption features. – roaima Aug 1 at 21:46
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TL;DR

Yes, an ext4 external HDD can be mounted on any recent Linux PC.

The long version:

  • root will have access to everything
  • individual user's access will be unpredictable unless both Linux PCs have the exact same users defined in the exact same order. (very low probability of this happening all by itself)¹

Note 1: This is because the usernames are just labels for the users themselves, not the system: Rhe system operates on user ID (uid) so if "Alice" is user 1000 on system_a and "Bob" is 1001, but on system_b "Bob" is 1000 and "Alice" is 1001, their permissions will be reversed if an external HDD created on system_a is inserted into system_b

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    Good idea mentioning this. To clarify for those who don't know, this is because the usernames are pretty much only for the users themselves, not the system. The system operates on user ID (uid) so if Alice is user 1000 on one system and Bob is 1001, but on another system Bob is 1000 and Alice is 1001, their permissions will be reversed (for example in the case of an external drive). – static Aug 1 at 18:39
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    @Fabby - 'root will have access to everything'. If someone with linux-pc ... takes my 'password-protected-ext4-usb-flash-drive' and mount it on his linux-pc, opens his terminal as root could he access my files regardless of the fact that I have put a password on my 'usb-flash-drive'? – ccsann Aug 2 at 6:06
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    @md-sqa That would be a totally different and according to our rules here, a new question. As you're new on this site, please don't edit your question to include [Solved] but instead don't forget to click the grey at the left of the answer that is the most useful of all! ;-) – Fabby Aug 2 at 6:56
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    @Fabby Please go ahead! – static Aug 2 at 16:38
  • @static Done! Thanks! +30 :-) – Fabby Aug 3 at 14:59
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Any storage device can be opened on any other computer system provided the operating system supports that file system.

For EXT4, usually but possibly not. Yes if it is RHEL/CentOS 7.x or SLES 12.x. I know SLES 11.4 for example had limited support for EXT4, and SLES 11.3 I don't think had any support for EXT4. As we get further into the future and EXT4 becomes more universal then a more solid yes.

EXT3 for example a very likely yes for any linux system because that file system has been around enough where it is supported everywhere, as well as EXT2 and XFS.

Microsoft Windows does not support it so connecting EXT4 formatted storage to anything Microsoft Windows would be a no {i know u did not ask this}.

With the Microsoft NTFS file system that can be mounted as read/write on a linux system if the ntfs-3g file system driver is installed and working; linux does not natively support the NTFS file system you have to go out and manually get/install that specific file system driver so the operating system can understand and make use of that kind of file system.

with the ntfs-3g driver for linux that may possibly make NTFS the most universal when considering Microsoft Windows, but for linux only system EXT3 may currently be a better choice over EXT4 considering if an older linux system is being used that has no software support for EXT4. And XFS might be the most widely supported.

  • "connecting EXT4 formatted storage to anything Microsoft Windows would be a no". Oh dear; I'd better stop doing this, then. (Third party FOSS software.) – roaima Aug 3 at 23:09

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