mkfs.ext4

What it does

mkfs.ext4 is mke2fs -t ext4. ext4 can grow (also mounted) and shrink (only unmounted) with resize2fs. By default 5 % of the blocks are reserved for root (-m), so root can still work when users fill the disk.

How to write it

mkfs.ext4 [OPTION]... DEVICE [SIZE]

Options 30

Most used

-L LABEL: Set a label (max 16 characters).
-m PERCENT: Reserved blocks for root (default 5).
-t TYPE: ext2, ext3 or ext4 (with mke2fs).
-T USAGE: Usage type from mke2fs.conf: news, largefile, largefile4, small, floppy.
-b SIZE: Block size (1024, 2048, 4096).
-i BYTES: Bytes per inode (smaller = more inodes).
-N NUMBER: Number of inodes.
-I SIZE: Inode size.
-U UUID: Set the UUID.
-O FEATURES: Turn features on or off (^feature = off), like ^has_journal.
-E OPTIONS: Extended options: stride=, stripe_width=, lazy_itable_init=, nodiscard …
-j: Create a journal (ext3).
-J OPTIONS: Journal options (size=, device=).
-e continue|remount-ro|panic: What to do on errors.
-c: Check for bad blocks first.
-l FILE: Read bad blocks from a file.
-g N, -G N: Blocks per group / groups per flex group.
-C SIZE: Cluster size (bigalloc).
-d DIR: Copy this folder into the new file system.
-M DIR: Last mounted directory.
-o OS: Creator OS.
-r REVISION: File system revision.
-S: Write only superblock and group descriptors (rescue, dangerous).
-D: Use direct I/O.
-z FILE: Save an undo file.
-n: Dry run: show what would happen.
-F: Force.
-q: Quiet.
-v: Verbose.
-V: Show the version.

Examples 10

$ run as a normal user# run as root (or with sudo)

1Create ext4
```
#mkfs.ext4 /dev/vdb2
```
Asks before overwriting an existing file system.
2With a label
```
#mkfs.ext4 -L backup /dev/vdb2
```
Mount with LABEL=backup.
3Less reserved space on a data disk
```
#mkfs.ext4 -m 1 /dev/vdb2
```
1 % instead of 5 % (big disks waste a lot with 5 %).
4Many small files
```
#mkfs.ext4 -T small /dev/vdb2
```
More inodes (mail or cache folders).
5Large files only
```
#mkfs.ext4 -T largefile4 /dev/vdb2
```
Fewer inodes, more space for data.
6Dry run
```
#mkfs.ext4 -n /dev/vdb2
```
Shows the backup superblock positions — useful for repair.
7ext3 or ext2
```
#mke2fs -t ext3 /dev/vdb3
```
Older formats, for old systems.
8Fast create on big devices
```
#mkfs.ext4 -E lazy_itable_init=1,nodiscard /dev/vdb2
```
Finishes the inode tables in the background.

9Check the result

#dumpe2fs -h /dev/vdb2 | grep -E 'volume name|Reserved block|Inode count'

Settings of the new file system.

10Change settings later
```
#tune2fs -m 1 -L data2 /dev/vdb2
```
No need to recreate.

Files

/etc/mke2fs.conf: Defaults and usage types.

Exit codes

0 :: Done. 1 :: Error.

`mkfs.ext4`

What it does

How to write it

Options 30

Examples 10

1Create ext4

2With a label

3Less reserved space on a data disk

4Many small files

5Large files only

6Dry run

7ext3 or ext2

8Fast create on big devices

9Check the result

10Change settings later

Files

Exit codes

Full manual

What it does

How to write it

Options 30

Examples 10

1Create ext4

2With a label

3Less reserved space on a data disk

4Many small files

5Large files only

6Dry run

7ext3 or ext2

8Fast create on big devices

9Check the result

10Change settings later

Files

Exit codes

Related commands

Used in these lessons

Used in these labs

Full manual

`mkfs.ext4`