How do I know if a partition is ext2, ext3, or ext4?

Question

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?

Solution 1

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. Sometimes you'll need the -L flag as well, if the device file name is a symbolic link. You'll see output like this:

# file -sL /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.

Solution 2

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"

Solution 3

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

Solution 4

Surprised this isn't on here already. No sudo required:

lsblk -f

Solution 5

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.

View more solutions

Comments

[zacharyalexstern]

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.

[Ciro Santilli Путлер Капут 六四事]

unix.stackexchange.com/questions/34623/…

[user2935706]

parted is not installed. Also the drives are not mounted yet.

[tonybka]

@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.

[Warren Young]

This has the same weakness as h3rmiller's mount based answer.

[Warren Young]

+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]

+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]

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.

[mattdm]

@Warren: That's because it is an ext4 filesystem in that case. Just one with not many features.

[Warren Young]

@mattdm: So when you unmount it...is it still an ext4 filesystem?

[mattdm]

@Warren: in a sense, all ext2 filesystems are also ext4 filesystems, yes. (But of course, not in the sense most people mean.)

[Warren Young]

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.

[user2935706]

While this is not the most upvoted answer, this is the one I actually use. Also I do not need to specify the device.

[user2935706]

+1 for effort. I have done fdisk before asking this question. Keep points up.

[heinrich5991]

When entering $ sudo file /dev/sda1, I get /dev/sda1: block special

[Warren Young]

In that case, I've been using ext4 since 1993 or so, in Yggdrasil Linux. I'm probably using ext5 already. Woohoo, I live in the FUTURE!

[Cannon8668]

doesn't work for LVM stuff: parted -l seems to work better

[Gilles 'SO- stop being evil']

@TiloBunt It works for LVM as well. The device name will be /dev/VOLUMEGROUP/LOGICALVOLUME or /dev/mapper/VOLUMEGROUP-LOGICALVOLUME instead of /dev/sdLETTERDIGIT.

[Gilles 'SO- stop being evil']

@TiloBunt Make that file -sL /dev/mapper/foo-bar, with the -L flag to dereference the symlink.

[Jose Diaz-Gonzalez]

For what its worth, this also appears to work for xfs drives, though apparently it's blkid is not as great as lsblk is at detecting unmounted drives (if you need to)

[iTag]

If I run this without sudo the FSTYPE column is blank.

[Freedom_Ben]

@Flup I just tried it myself again and it worked perfectly without sudo. FSTYPE column was fully populated. May be some disparity between our systems?

[don_crissti]

@Flup - you must be using Debian/Ubuntu or derivatives... They're famous for doing something (or maybe not doing something, I wouldn't know) and the end result is you need root privileges to list some lsblk columns...

[Basile Starynkevitch]

Because it is not the best answer: a partition might be grub-labeled as ext2 and contains ext4 filesystem (and then would be mounted as ext4 with mount -t auto)

[Brain2000]

Thanks! The file command wasn't working, but this gave me what I needed.

[rectalogic]

I've been using this technique for years. But today it failed because the unformatted EBS volume happens to match the signature of a DOS executable:$ sudo file -s /dev/xvdm /dev/xvdm: DOS executable (COM)

[Gilles 'SO- stop being evil']

@rectalogic file guesses, and sometimes it can guess wrong. When you know what kind of file you're looking at (e.g. you know that it's a filesystem image) it works reasonably well. When it's open-ended, such as in your case with a volume that contained “random” garbage, there can be false positives. COM executables don't actually have any structure, so there file has both many false positives and many false negatives.

[rectalogic]

I've switched to using blkid -o value -s TYPE /dev/xvdm - it exits with 2 if the device is unformatted, otherwise prints the filesystem, and works with LUKS encrypted filesystems.

[jokab]

i had to sudo blkid /dev/sda1 else I get blank results

[zer09]

Best answer for me, using without sudo, also works on Debian/Ubuntu derivatives, I am on Pop Os.

[Vishnu Dasu]

FEATURE_BLKID_TYPE must be enabled to use BusyBox blkid in this manner.