Linux – Check disk image file system type

disk-imagefilesystemslinux

How could I check the file system format of a disk image?

I know that I can check with the file command but I would like to automate the behaviour.

$ file img.raw
img.raw:   data

$ file img.ext4
img.raw:   Linux rev 1.0 ext4 filesystem data, UUID=346712e7-1a56-442b-a5bb-90ba4c6cc663 (extents) (64bit) (large files) (huge files)

$ file img.vfat
img.vfat:  DOS/MBR boot sector, code offset 0x3c+2, OEM-ID "mkfs.fat", sectors/cluster 16, reserved sectors 16, root entries 512, Media descriptor 0xf8, sectors/FAT 256, sectors/track 32, heads 64, sectors 1024000 (volumes > 32 MB) , serial number 0x4b5e9a12, unlabeled, FAT (16 bit)

I would like to check if the given image disk is formatted with the given format.

For example checkfs <image> <format> returns 0 if the image contains a 'format' file system, another value otherwise.

I thought about doing something like file <image> | grep <format> and check the return code, however for vfat filesystems, 'vfat' is not appearing on file's output.

I could also write a script to do it but I can't find tools which allow me to get the file system format of a disk image.

I've also tried with the following tools: fdisk, parted, and df.

Is there a tool which would allow me to check a disk image file system format and that works with most used file system formats?

Best Answer

Finally found what I needed

blkid -o value -s TYPE <image> will return the fs type or nothing if it's raw data.

EDIT:

As mentioned by @psusi, parted has a machine parsable output. I find it less convenient than using blkid but it could also be useful.

parted -m <image> print | tail -n +3 | awk -F ":" '{print $(NF-2)}' will print the fs type of each partition.

tail -n +3 is used to skip the two first lines
awk -F ":" '{print $(NF-2)}' is used to get the fs type which is the third last element starting from the end

Related Solutions

Filesystems – How to Create Small Disk Image with Large Partitions

Firstly, writing a sparse image to a disk will not result in anything but the whole of the size of that image file - holes and all - covering the disk. This is because handling of sparse files is a quality of the filesystem - and a raw device (such as the one to which you write the image) has no such thing yet. A sparse file can be stored safely and securely on a medium controlled by a filesystem which understands sparse files (such as an ext4 device) but as soon as you write it out it will envelop all that you intend it to. And so what you should do is either:

Simply store it on an fs which understands sparse files until you are prepared to write it.
Make it two layers deep...
- Which is to say, write out your main image to a file, create another parent image with an fs which understands sparse files, then copy your image to the parent image, and...
- When it comes time to write the image, first write your parent image, then write your main image.

Here's how to do 2:

Create a 1GB sparse file...
```
dd bs=1kx1k seek=1k of=img </dev/null
```
Write two ext4 partitions to its partition table: 1 200MB, 2 800MB...
```
printf '%b\n\n\n\n' n '+200M\nn\n' 'w\n\c' | fdisk img
```

Create two ext4 filesystems on a -Partitioned loop device and put a copy of the second on the first...

sudo sh -c '
    for p in "$(losetup --show -Pf img)p"*        ### the for loop will iterate
    do    mkfs.ext4 "$p"                          ### over fdisks two partitions
          mkdir -p ./mnt/"${p##*/}"               ### and mkfs, then mount each
          mount "$p" ./mnt/"${p##*/}"             ### on dirs created for them
    done; sync; cd ./mnt/*/                       ### next we cp a sparse image
    cp --sparse=always "$p" ./part2               ### of part2 onto part1
    dd bs=1kx1k count=175 </dev/zero >./zero_fill ### fill out part1 w/ zeroes
    sync; cd ..; ls -Rhls .                       ### sync, and list contents
    umount */; losetup -d "${p%p*}"               ### last umount, destroy
    rm -rf loop*p[12]/ '                          ### loop devs and mount dirs

mke2fs 1.42.12 (29-Aug-2014)
Discarding device blocks: done
Creating filesystem with 204800 1k blocks and 51200 inodes
Filesystem UUID: 2f8ae02f-4422-4456-9a8b-8056a40fab32
Superblock backups stored on blocks:
    8193, 24577, 40961, 57345, 73729

Allocating group tables: done
Writing inode tables: done
Creating journal (4096 blocks): done
Writing superblocks and filesystem accounting information: done

mke2fs 1.42.12 (29-Aug-2014)
Discarding device blocks: done
Creating filesystem with 210688 4k blocks and 52752 inodes
Filesystem UUID: fa14171c-f591-4067-a39a-e5d0dac1b806
Superblock backups stored on blocks:
    32768, 98304, 163840

Allocating group tables: done
Writing inode tables: done
Creating journal (4096 blocks): done
Writing superblocks and filesystem accounting information: done

175+0 records in
175+0 records out
183500800 bytes (184 MB) copied, 0.365576 s, 502 MB/s
./:
total 1.0K
1.0K drwxr-xr-x 3 root root 1.0K Jul 16 20:49 loop0p1
   0 drwxr-xr-x 2 root root   40 Jul 16 20:42 loop0p2

./loop0p1:
total 176M
 12K drwx------ 2 root root  12K Jul 16 20:49 lost+found
 79K -rw-r----- 1 root root 823M Jul 16 20:49 part2
176M -rw-r--r-- 1 root root 175M Jul 16 20:49 zero_fill

./loop0p1/lost+found:
total 0

./loop0p2:
total 0

Now that's a lot of output - mostly from mkfs.ext4 - but notice especially the ls bits at the bottom. ls -s will show the actual -size of a file on disk - and it is always displayed in the first column.

Now we can basically reduce our image to only the first partition...

fdisk -l img

Disk img: 1 GiB, 1073741824 bytes, 2097152 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0xc455ed35

Device Boot  Start     End Sectors  Size Id Type
img1          2048  411647  409600  200M 83 Linux
img2        411648 2097151 1685504  823M 83 Linux

There fdisk tells us there are 411647 +1 512 byte sectors in the first partition of img...
```
dd seek=411648 of=img </dev/null
```

That truncates the img file to only its first partition. See?

ls -hls img

181M -rw-r--r-- 1 mikeserv mikeserv 201M Jul 16 21:37 img

...but we can still mount that partition...

sudo mount "$(sudo losetup -Pf --show img)p"*1 ./mnt

...and here are its contents...

ls -hls ./mnt

total 176M
 12K drwx------ 2 root root  12K Jul 16 21:34 lost+found
 79K -rw-r----- 1 root root 823M Jul 16 21:34 part2
176M -rw-r--r-- 1 root root 175M Jul 16 21:34 zero_fill

And we can append the stored image of the second partition to the first...

sudo sh -c '
    dd seek=411648 if=./mnt/part2 of=img
    umount ./mnt; losetup -D
    mount "$(losetup -Pf --show img)p"*2 ./mnt
    ls ./mnt; umount ./mnt; losetup -D'

1685504+0 records in
1685504+0 records out
862978048 bytes (863 MB) copied, 1.96805 s, 438 MB/s
lost+found

Now that has grown our img file: it's no longer sparse...

ls -hls img

1004M -rw-r--r-- 1 mikeserv mikeserv 1.0G Jul 16 21:58 img

...but removing that is as simple the second time as it was the first, of course...

dd seek=411648 of=img </dev/null
ls -hls img

181M -rw-r--r-- 1 mikeserv mikeserv 201M Jul 16 22:01 img

Linux – How to Disk Copy with Unreadable Sectors

Do not reinvent the wheel. Use ddrescue.

GNU ddrescue is a data recovery tool. It copies data from one file or block device (hard disc, cdrom, etc) to another, trying to rescue the good parts first in case of read errors.

Do not trust dd conv=sync,noerror, unless you really know how it works.

Best Answer

Related Solutions

Filesystems – How to Create Small Disk Image with Large Partitions

Linux – How to Disk Copy with Unreadable Sectors

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