tune2fs command is one of the advanced unix commands which allows you to adjust various tunable parameters of the ext2/ext3 filesystems. Naturally, it also helps you confirm the existing parameters configured for your filesystems.
Confirm current filesystem parameters with tune2fs
The tunefs -l command will show you all the information contained in a filesystem’s superblock. Here’s how it typically looks:
ubuntu# tune2fs -l /dev/sda1
tune2fs 1.40-WIP (14-Nov-2006)
Filesystem volume name: <none>
Last mounted on: <not available>
Filesystem UUID: d2ff8a06-74b7-4877-9d37-1873414e25b3
Filesystem magic number: 0xEF53
Filesystem revision #: 1 (dynamic)
Filesystem features: has_journal filetype needs_recovery sparse_super
Default mount options: (none)
Filesystem state: clean
Errors behavior: Continue
Filesystem OS type: Linux
Inode count: 2490368
Block count: 4980736
Reserved block count: 249036
Free blocks: 3417990
Free inodes: 2401957
First block: 0
Block size: 4096
Fragment size: 4096
Blocks per group: 32768
Fragments per group: 32768
Inodes per group: 16384
Inode blocks per group: 512
Filesystem created: Wed Sep 26 02:30:22 2007
Last mount time: Tue Apr 1 00:17:16 2008
Last write time: Tue Apr 1 00:17:16 2008
Mount count: 1
Maximum mount count: 29
Last checked: Tue Apr 1 00:16:22 2008
Check interval: 15552000 (6 months)
Next check after: Sun Sep 28 00:16:22 2008
Reserved blocks uid: 0 (user root)
Reserved blocks gid: 0 (group root)
First inode: 11
Inode size: 128
Journal inode: 8
Default directory hash: tea
Directory Hash Seed: c0c5742c-980a-49b2-ae0b-4e96895376b6
Journal backup: inode blocks
Reserved space on a Unix filesystem
By default, every filesystem in Unix has some space reserved for the superuser (root). This means that no regular Unix user can fill your filesystem up to 100%, and so it’s always going to have enough free space to continue normal function.
As a standard, each filesystem has 5% of space reserved in this way. If you look at the above output, you may notice the following lines there, which regulate the space reservation:
this 249036 reserve is exactly 5%. The uid and gid confirm the Unix user id and Unix group id of the user who will be allowed to tap into the reserved space. As I said earlier, it’s root.
If you have root access on your system, you can alter this reserved space allocation for any filesystem using tune2fs -m parameter, by specifying the percentage of the space to be reserved.
Here’s how we change the default reserve to be 6% of the overall filesystem size:
From this example, you can see that the default block size for the filesystem on /dev/sda1 partition is 4096 bytes, or 4k. That’s the default block size for ext3 filesystem.
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