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I just formatted stuff. One disk I format as ext2. The other I want to format as ext4. I want to test how they perform.

Now, how do I know the kind of file system in a partition?

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2  
Out of curiosity, what are you trying to test? Journal vs. no journal? For the record, you can operate ext4 in no-journal mode, and still benefit from all the other new features. –  zacharyalexstern Jan 15 '13 at 15:36

6 Answers 6

up vote 25 down vote accepted

How do I tell what sort of data (what data format) is in a file?
→ Use the file utility.

Here, you want to know the format of data in a device file, so you need to pass the -s flag to tell file not just to say that it's a device file but look at the content. You'll see output like this:

# file -s /dev/sd*
/dev/sda1: Linux rev 1.0 ext4 filesystem data, UUID=63fa0104-4aab-4dc8-a50d-e2c1bf0fb188 (extents) (large files) (huge files)
/dev/sdb1: Linux rev 1.0 ext2 filesystem data, UUID=b3c82023-78e1-4ad4-b6e0-62355b272166
/dev/sdb2: Linux/i386 swap file (new style), version 1 (4K pages), size 4194303 pages, no label, UUID=3f64308c-19db-4da5-a9a0-db4d7defb80f

Given this sample output, the first disk has one partition and the second disk has two partitions. /dev/sda1 is an ext4 filesystem, /dev/sdb1 is an ext2 filesystem, and /dev/sdb2 is some swap space (about 4GB).

You must run this command as root, because ordinary users may not read disk partitions directly: if needed, add sudo in front.

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+1: Cuuuute. :) –  Warren Young Jan 9 '13 at 18:23
    
When entering $ sudo file /dev/sda1, I get /dev/sda1: block special –  heinrich5991 Jan 10 '13 at 16:55
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@heinrich5991 “you need to pass the -s flag …”. I show the command file -s /dev/sd* − with sudo in front, that's sudo file -s /dev/sd*. –  Gilles Jan 10 '13 at 16:57
    
Oh sorry, I overlooked that. :( –  heinrich5991 Jan 10 '13 at 20:35

Another option is to use blkid:

$ blkid /dev/sda1
/dev/sda1: UUID="625fa1fa-2785-4abc-a15a-bfcc498139d1" TYPE="ext2"

This recognizes most filesystem types and stuff like encrypted partitions.

You can also search for partitions with a given type:

# blkid -t TYPE=ext2
/dev/sda1: UUID="625fa1fa-2785-4abc-a15a-bfcc498139d1" TYPE="ext2" 
/dev/sdb1: UUID="b80153f4-92a1-473f-b7f6-80e601ae21ac" TYPE="ext2"
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+1: I've verified that this gives the correct result when mounting an ext2 filesystem with mount -t ext4. blkid isn't fooled by that. –  Warren Young Jan 9 '13 at 16:45

You can use sudo parted -l

[shredder12]$ sudo parted -l

Model: ATA WDC WD1600BEVT-7 (scsi)
Disk /dev/sda: 160GB
Sector size (logical/physical): 512B/512B
Partition Table: msdos

Number  Start   End     Size    Type      File system     Flags
 1      32.3kB  8587MB  8587MB  primary   ext3            boot
 4      8587MB  40.0GB  31.4GB  primary   ext4
 2      40.0GB  55.0GB  15.0GB  primary   ext4
 3      55.0GB  160GB   105GB   extended
 5      55.0GB  158GB   103GB   logical   ext4
 6      158GB   160GB   1999MB  logical   linux-swap(v1)

Source

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1  
parted is not installed. Also the drives are not mounted yet. –  Jim Thio Jan 9 '13 at 10:45
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@JimThio I assume you were able to install it? You should be able to get it by simply doing sudo apt-get install parted (or gparted) if you are on Ubuntu or any other debian derivative. –  Karthik T Jan 9 '13 at 12:24
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+1: I've verified that this gives the correct result when mounting an ext2 filesystem with mount -t ext4. parted isn't fooled by that. –  Warren Young Jan 9 '13 at 16:45
    
While this is not the most upvoted answer, this is the one I actually use. Also I do not need to specify the device. –  Jim Thio Jan 10 '13 at 2:34

Still another way, since you know you're running some flavor of ext?, is to look at the filesystem's feature list:

# tune2fs -l /dev/sda1 | grep features

If in the list you see:

  • extent — it's ext4
  • no extent, but has_journal — it's ext3
  • neither extent nor has_journal — it's ext2

The parted and blkid answers are better if you want these heuristics run for you automatically. (They tell the difference with feature checks, too.) They can also identify non-ext? filesystems.

This method has the virtue of showing you the low-level differences.

The important thing to realize here is that these three filesystems are forwards compatible, and to some extent backwards-compatible, too. Later versions just add features on top of the older ones.

See the ext4 HOWTO for more information on this.

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try using df -T see man df for more options still one more way I found is cfdisk

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2  
This has the same weakness as h3rmiller's mount based answer. –  Warren Young Jan 9 '13 at 16:38
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h3rrmiller removed his answer, so for those who don't have the rep to see it now, the problem is that if you say mount -t ext4 on an ext2 filesystem, df -T reports ext4. That is, it's just reading what the mount table says, not looking at the filesystem metadata to figure this out. –  Warren Young Jan 9 '13 at 18:19
    
@Warren: That's because it is an ext4 filesystem in that case. Just one with not many features. –  mattdm Jan 9 '13 at 19:05
    
@mattdm: So when you unmount it...is it still an ext4 filesystem? –  Warren Young Jan 9 '13 at 19:26
    
@Warren: in a sense, all ext2 filesystems are also ext4 filesystems, yes. (But of course, not in the sense most people mean.) –  mattdm Jan 9 '13 at 19:32

fdisk -l will list

Usage:

fdisk [options] -l list partition table(s) fdisk -s give partition size(s) in blocks fdisk [options] change partition table

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1  
On what system? fdisk, on the system I'm using at the moment at least, only shows the partition type, not the filesystem type. That means not only can't it tell the difference between ext2, ext3, and ext4, it also can't discern ReiserFS or XFS from these. –  Warren Young Jan 9 '13 at 20:17
    
+1 for effort. I have done fdisk before asking this question. Keep points up. –  Jim Thio Jan 10 '13 at 2:35

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