104.2 Maintain the integrity of filesystems edit

Candidates should be able to maintain a standard filesystem, as well as the extra data associated with a journalling filesystem.

Key Knowledge Areas

  • Verify the integrity of filesystems.
  • Monitor free space and inodes[check spelling].
  • Repair simple filesystem problems.

Once a filesystem has been created on your block device you will want to know how to monitor the filesystem and check it for errors, recovering from errors where possible. Fortunately the filesystem provide several command and utilities to aid in this process.

Monitoring Disk Usage edit

The df (disk free) and disk usage (du) commands can be used to report on the amount of free disk space and query how much space directories and files are using. df works on a device level, as opposed to a directory level.

The df tool shows used and available disk space. By default this is given in blocks of 1K.

$ df -h

Filesystem Size Used Avail Use% Mounted on

/dev/hda9 289M 254M 20M 93% /

/dev/hda2 23M 7.5M 14M 35% /boot

none 62M 0 61M 0% /dev/shm

/dev/hda5 1.4G 181M 1.1G 13% /share

/dev/hda7 787M 79M 669M 11% /tmp

/dev/hda3 4.3G 3.4G 813M 81% /usr

/dev/hda6 787M 121M 627M 17% /var

// 8.8G 3.7G 71% /mnt/smb

The du command will display disk usage. This is done on a per directory basis. du cannot display available space since this information is only available at a device level.

The following command will list the current usage of the /etc directory in human readable units (using the -h switch) and will only print the grand total (using the -s switch):

# du -sh /etc

62M /etc/

File System Checking, Repair and Maintenance edit

As with filesystem monitoring there are numerous tools for maintaining a Linux filesystem which are provided by the creators of the respective filesystem.

If the file system is damaged or corrupt, then the fsck utility should be run against the partition (the minimum requirement is that the file system be unmounted or mounted read-only).

fsck acts as a front that automatically detects the file system type of a partition. Then as with mkfs, the tools fsck.ext2, fsck.ext3 fsck.ext4 or fsck.xfs will be called accordingly to carry out the system check and, if necessary, repair. Since ext3 is the main filesystem type for Linux there is a e2fsck command that only handles this filesystem type. You invoke the filesystem check as follows explicitly specify a file system type with the following syntax:

fsck –t <fstype> <device>

Example: Checking a reiserfs filesystem on the /dev/sdb10 device:

# fsck –t reiserfs /dev/sdb10

# fsck.reiserfs /dev/sdb10

Ext File System Maintenance utilities

As the extended filesystem is the most widely used and deployed filesystem on Linux, the tools for ext filesystem support are more numerous and comprehensive than for other filesystems.

Ext File System Debug Commands

The debugfs and dumpe2fs are seldom used but can be useful in providing low level information about an ext2, ext3 or ext4 filesystem.

debugfs [ -b blocksize ] [ -s superblock ] [ -f cmd_file ] [ -R request ] [ -V ] [ [ -w ] [ -c ] [ -i ] [ device ] ]

The debugfs program is an interactive file system debugger. It can be used to examine and change the state of an ext2/3/4 file system.

Once in the debugfs shell, internal commands can then be used to change directory, examine inode data, remove files, create links, dump the ext3 journal logs etc. While this is a very powerful command, it should be used with caution, generally only after the fsck command has failed to make any headway.

dumpe2fs [ -bfhixV ] [ -ob superblock ] [ -oB blocksize ] device

dumpe2fs prints the super block and block group information for the filesystem present on device.

dumpe2fs /dev/hda1

dumpe2fs 1.35 (28-Feb-2004)

Filesystem volume name: /boot1

Last mounted on: <not available>

Filesystem UUID: d741042c-3eaf-49ee-94c1-7dd8c5459764

Filesystem magic number: 0xEF53

Filesystem revision #: 1 (dynamic)

Filesystem features: has_journal ext_attr resize_inode dir_index filetype needs_recovery sparse_super

Default mount options: (none)

Filesystem state: clean

Errors behavior: Continue

Filesystem OS type: Linux

Inode count: 25584

Block count: 102280

Reserved block count: 5114

Free blocks: 80564

Free inodes: 25537

First block: 1

Block size: 1024

Fragment size: 1024

Reserved GDT blocks: 256

Blocks per group: 8192

Fragments per group: 8192

Inodes per group: 1968

Inode blocks per group: 246

Filesystem created: Sat May 7 10:40:51 2005

Last mount time: Sun May 29 04:08:01 2005

Last write time: Sun May 29 04:08:01 2005

Mount count: 10

Maximum mount count: -1

Last checked: Sat May 7 10:40:51 2005

Check interval: 0 (<none>)

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: 50108791-6a0a-41ff-9608-0485c993eaf9

Journal backup: inode blocks

Group 0: (Blocks 1-8192)

Primary superblock at 1, Group descriptors at 2-2

Block bitmap at 259 (+258), Inode bitmap at 260 (+259)

Inode table at 261-506 (+260)

0 free blocks, 1942 free inodes, 2 directories

Free blocks:

Free inodes: 27-1968



tune2fs allows you to adjust various filesystem parameters on Linux extended filesystems. The following is a list of the most common parameters used to adjust extended filesystem settings:

  • -c sets the number of times a filesystem will be mounted before a filesystem check is forced. This is usually at next boot but can be run when a filesystem is manually unmounted.
  • -C sets the number of times the filesystem was mounted since it was last checked.
  • -L sets the volume label, this used to be used to uniquely identify hard disk partitions but is being replaced with UUIDs.
  • -i sets the maximum time between filesystem checks. A filesystem check will be forced when either the time expires or the maximum number of mounts has been exceeded, which ever comes first.
  • -j adds journaling to an ext2 filesysem making it an ext3 filesystem.

Running tune2fs -l will print out the current settings for a filesystem.

tune2fs 1.41.11 (14-Mar-2010)

Filesystem volume name: <none>

Last mounted on: /

Filesystem UUID: 6f4746c6-777e-4937-92ee-de98cf8f5aa4

Filesystem magic number: 0xEF53

Filesystem revision #: 1 (dynamic)

Filesystem features: has_journal ext_attr resize_inode dir_index filetype needs_recovery extent flex_bg sparse_super large_file huge_file uninit_bg dir_nlink extra_isize

Filesystem flags: signed_directory_hash

Default mount options: (none)

Filesystem state: clean

Errors behavior: Continue

Filesystem OS type: Linux

Inode count: 26558464

Block count: 106205707

Reserved block count: 5310285

Free blocks: 62912050

Free inodes: 25721258

First block: 0

Block size: 4096

Fragment size: 4096

Reserved GDT blocks: 998

Blocks per group: 32768

Fragments per group: 32768

Inodes per group: 8192

Inode blocks per group: 512

RAID stride: 32747

Flex block group size: 16

Filesystem created: Sat Feb 13 00:48:21 2010

Last mount time: Tue Sep 28 07:27:39 2010

Last write time: Tue Sep 21 09:14:03 2010

Mount count: 22

Maximum mount count: 25

Last checked: Tue Sep 21 09:14:03 2010

Check interval: 15552000 (6 months)

Next check after: Sun Mar 20 09:14:03 2011

Lifetime writes: 709 GB

Reserved blocks uid: 0 (user root)

Reserved blocks gid: 0 (group root)

First inode: 11

Inode size: 256

Required extra isize: 28

Desired extra isize: 28

Journal inode: 8

First orphan inode: 404853

Default directory hash: half_md4

Directory Hash Seed: 982f8e6c-db49-49b0-8f65-bce3725b5196

Journal backup: inode blocks

XFS File System Maintenance Utilities

The tools that come with XFS for filesystem integrity checking are xfs_info and xfs_metadump.

xfs_metdump is a filesystem debugging utility, that dumps xfs filesystem meta-data to a file. The file can then be used to debug the files or as a backup. Later the meta-data can be restored with the xfs_restore utility.

Used files, terms and utilities:* du

  • df
  • fsck
  • e2fsck
  • mke2fs
  • debugfs
  • dumpe2fs
  • tune2fs
  • xfs tools (such as xfs_metadump and xfs_info)

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