104.2. Maintain the integrity of filesystems

Weight: 2
Description: Candidates should be able to maintain a standard filesystem, as well as the extra data associated with a journaling filesystem.
Key Knowledge Areas:
  • Verify the integrity of filesystems
  • Monitor free space and inodes
  • Repair simple filesystem problems
Terms and Utilities:
  • du
  • df
  • fsck
  • e2fsck
  • mke2fs
  • debugfs
  • dumpe2fs
  • tune2fs
  • XFS tools (such as xfs_metadump and xfs_info)
In cases when your system crashes or loses power, your filesystems may be left in an inconsistent state, with some changes completed and some not.
Operating with a damaged filesystem is not a good idea as you are likely to further compound any existing errors.We’ll take a look at some tools to help us manage such problems.
You should always back up your filesystem before attempting any repairs!


The main tool for checking and repairing filesystems is fsck, which, like mkfs, is really a front end to filesystem-checking routines for the various filesystem types.
root@ubuntu16-1:~# fsck
fsck fsck.ext3 fsck.fat fsck.nfs
fsck.cramfs fsck.ext4 fsck.minix fsck.vfat
fsck.ext2 fsck.ext4dev fsck.msdos
root@ubuntu16-1:~# ls /sbin/fsck*
/sbin/fsck /sbin/fsck.ext3 /sbin/fsck.fat /sbin/fsck.nfs
/sbin/fsck.cramfs /sbin/fsck.ext4 /sbin/fsck.minix /sbin/fsck.vfat
/sbin/fsck.ext2 /sbin/fsck.ext4dev /sbin/fsck.msdos
Some of these are just links to e2fsck command and they are the same
The fsck command in Linux allows us to manually check for file system inconsistencies, Fsck command needs to be run with superuser privileges or root(ubuntu 16.04 here):
root@ubuntu16-1:~# fsck /dev/sda1
fsck from util-linux 2.27.1
e2fsck 1.42.13 (17-May-2015)
/dev/sda1 is mounted.
e2fsck: Cannot continue, aborting.
In order to use fsck the partition should be unmounted, otherwise it might cause damages!
Lets simply check file system on an unmounted ext3 partition (sdb1) and try to fix errors :
root@ubuntu16-1:~# fsck /dev/sdb1
fsck from util-linux 2.27.1
e2fsck 1.42.13 (17-May-2015)
/dev/sdb1: clean, 11/1310720 files, 126322/5242624 blocks
This command will attempt to check /dev/sdb1, and report any errors it finds.The exit code returned by fsck is one of following conditions:
  • 0 No errors
  • 1 Filesystem errors corrected
  • 2 System should be rebooted
  • 4 Filesystem errors left uncorrected
  • 8 Operational error
  • 16 Usage or syntax error
  • 32 Checking canceled by user request
  • 128 Shared-library error
-N option just shows what would be executed but do not attempt to repair them:
root@ubuntu16-1:~# fsck -N /dev/sdb1
fsck from util-linux 2.27.1
[/sbin/fsck.ext3 (1) -- /dev/sdb1] fsck.ext3 /dev/sdb1
-n causes these commands not to fix anything and just show what was going to be done:
root@ubuntu16-1:~# fsck -n /dev/sdb1
fsck from util-linux 2.27.1
e2fsck 1.42.13 (17-May-2015)
/dev/sdb1: clean, 11/1310720 files, 126322/5242624 blocks
Normally, fsck will skip parts of the filesystem marked as "clean" — meaning all pending writes were successfully made. The -f ("force") option specifies that fsck should check parts of the filesystem even if they are not "dirty". The result is a less efficient, but a more thorough check.
root@ubuntu16-1:~# fsck -f /dev/sdb1
fsck from util-linux 2.27.1
e2fsck 1.42.13 (17-May-2015)
Pass 1: Checking inodes, blocks, and sizes
Pass 2: Checking directory structure
Pass 3: Checking directory connectivity
Pass 4: Checking reference counts
Pass 5: Checking group summary information
/dev/sdb1: 11/1310720 files (0.0% non-contiguous), 126322/5242624 blocks
What are inodes?
As we said Linux treating everything as a file (even the hardware devices). The keyboard, mouse, printers, monitor, hard disk, processes, even the directories are treated as files in Linux. The regular files contain data such as text (text files), music, videos (multimedia files) etc. Set aside the regular data, there are some other data about these files, such as their size, ownership, permissions, timestamp etc. This meta-data about a file is managed with a data structure known as an inode (index node).
We can also check file systems using their UUID.(use blkid command ):
root@ubuntu16-1:~# blkid /dev/sdb1
/dev/sdb1: UUID="b9ca56aa-4ea3-4f61-92c8-18c867fd991f" SEC_TYPE="ext2" TYPE="ext3" PARTUUID="4d71bc84-01"
root@ubuntu16-1:~# fsck -N UUID="b9ca56aa-4ea3-4f61-92c8-18c867fd991f"
fsck from util-linux 2.27.1
e2fsck 1.42.13 (17-May-2015)
/dev/sdb1: clean, 11/1310720 files, 126322/5242624 blocks
fsck command example
fsck -M /dev/sda1
prevents running fsck on mounted filesystem
fsck -t ext3 /dev/sdb1
Check Only a Specific Filesystem Type
fsck -y -f /dev/sdb1
pass “yes” to all the questions to fix
For checking a XFS filesystem, wehave to use xfs_check command

Advanced tools

There are several more advanced tools that we can use to examine or repair a filesystem.

Tools for ext2 and ext3 filesystems

  • tune2fs:Adjusts parameters on ext2 and ext3 filesystems. Use this to add a journal
  • dumpe2fs: shows all super blocks info
  • debugfs: interactive file system editor
Super Blocks
You may be wondering how all these checking and repairing tools know where to start. Linux and UNIX filesystems usually have a superblock, which describes the filesystem metadata, or data describing the filesystem itself. This is usually stored at a known location, frequently at or near the beginning of the filesystem, and replicated at other well-known locations. You can use the -n option of mke2fs to display the superblock locations for an existing filesystem.
root@ubuntu16-1:~# mke2fs -n /dev/sdb1
mke2fs 1.42.13 (17-May-2015)
/dev/sdb1 contains a ext3 file system
created on Sat Jan 25 22:17:24 2020
Proceed anyway? (y,n) y
Creating filesystem with 5242624 4k blocks and 1310720 inodes
Filesystem UUID: 28ce54ac-abbd-4788-bab8-b71eae9a53bc
Superblock backups stored on blocks:
32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208,


The ext family of file systems also has a utility called tune2fs, which can be used to inspect information about the block count as well as information about whether the filesystem is journaled (ext3 or ext4) or not (ext2).
The tune2fs command allows you to set assorted filesystem parameters on a mounted ext2 or ext3 filesystem.
-l shows contents of the filesystem superblock, including the current values of the parameters:
root@ubuntu16-1:~# tune2fs -l /dev/sdb1
tune2fs 1.42.13 (17-May-2015)
Filesystem volume name: <none>
Last mounted on: <not available>
Filesystem UUID: b9ca56aa-4ea3-4f61-92c8-18c867fd991f
Filesystem magic number: 0xEF53
Filesystem revision #: 1 (dynamic)
Filesystem features: has_journal ext_attr resize_inode dir_index filetype sparse_super large_file
Filesystem flags: signed_directory_hash
Default mount options: user_xattr acl
Filesystem state: clean
Errors behavior: Continue
Filesystem OS type: Linux
Inode count: 1310720
Block count: 5242624
Reserved block count: 262131
Free blocks: 5116302
Free inodes: 1310709
First block: 0
Block size: 4096
Fragment size: 4096
Reserved GDT blocks: 1022
Blocks per group: 32768
Fragments per group: 32768
Inodes per group: 8192
Inode blocks per group: 512
Filesystem created: Wed Jan 22 23:42:22 2020
Last mount time: n/a
Last write time: Thu Jan 23 02:21:07 2020
Mount count: 0
Maximum mount count: -1
Last checked: Thu Jan 23 02:21:07 2020
Check interval: 0 (<none>)
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
Default directory hash: half_md4
Directory Hash Seed: 73007ad4-213f-44cd-b8f0-4fbd0c1e90b2
Journal backup: inode blocks
The command can also be used to set many parameters or convert an ext2 filesystem to ext3 by adding a journal using -j option: tune2fs -j /dev/sdd1
Also we can use tune2fs for changing or modifying partition label:
root@ubuntu16-1:~# tune2fs -L myroot /dev/sda1
tune2fs 1.42.13 (17-May-2015)


dumpe2fs command is used to print the super block and blocks group information for the filesystem present on device.
printed information may be old or inconsistent when it is used with a mounted filesystem. Don’t forget to unmount your partition before using this command.
root@ubuntu16-1:~# dumpe2fs /dev/sdb1 | grep superblock
dumpe2fs 1.42.13 (17-May-2015)
Primary superblock at 0, Group descriptors at 1-2
Backup superblock at 32768, Group descriptors at 32769-32770
Backup superblock at 98304, Group descriptors at 98305-98306
Backup superblock at 163840, Group descriptors at 163841-163842
Backup superblock at 229376, Group descriptors at 229377-229378
Backup superblock at 294912, Group descriptors at 294913-294914
Backup superblock at 819200, Group descriptors at 819201-819202
Backup superblock at 884736, Group descriptors at 884737-884738
Backup superblock at 1605632, Group descriptors at 1605633-1605634
Backup superblock at 2654208, Group descriptors at 2654209-2654210
Backup superblock at 4096000, Group descriptors at 4096001-4096002


Is an interactive filesystem debugger. Use it to examine or change the state of an ext2 or ext3 filesystem. It opens the filesystem in read-only mode unless we tell it not to (with -w option).
if the filesystem is mounted, is alright for inspecting, but Do not attempt repair on a mounted filesystem.
root@ubuntu16-1:~# debugfs /dev/sda1
debugfs 1.42.13 (17-May-2015)
debugfs: cd /etc/
debugfs: pwd
[pwd] INODE: 1179649 PATH: /etc
[root] INODE: 2 PATH: /
debugfs: stat passwd
Inode: 1187630 Type: regular Mode: 0644 Flags: 0x80000
Generation: 2904697195 Version: 0x00000000:00000001
User: 0 Group: 0 Size: 2388
File ACL: 0 Directory ACL: 0
Links: 1 Blockcount: 8
Fragment: Address: 0 Number: 0 Size: 0
ctime: 0x5e2064c5:64a1019c -- Thu Jan 16 16:57:33 2020
atime: 0x5e2cb8a0:4aa345f8 -- Sun Jan 26 01:22:32 2020
mtime: 0x5e2064c5:64a1019c -- Thu Jan 16 16:57:33 2020
crtime: 0x5e2064c5:64a1019c -- Thu Jan 16 16:57:33 2020
Size of extra inode fields: 32
debugfs: ncheck 1187630
Inode Pathname
1187630 /etc/passwd
debugfs: q


xfs file system has it's own family commands. xfs_info is the same as tune2fs but for xfs.
xfs_info should be used on a mounted file system.
xfsprogs package must be installed
root@ubuntu16-1:~# xfs_info /dev/sdb1
meta-data=/dev/sdb1 isize=512 agcount=4, agsize=1310656 blks
= sectsz=512 attr=2, projid32bit=1
= crc=1 finobt=1 spinodes=0
data = bsize=4096 blocks=5242624, imaxpct=25
= sunit=0 swidth=0 blks
naming =version 2 bsize=4096 ascii-ci=0 ftype=1
log =internal bsize=4096 blocks=2560, version=2
= sectsz=512 sunit=0 blks, lazy-count=1
realtime =none extsz=4096 blocks=0, rtextents=0
xfs command
shows information
complete check of file system
check and fixes problems
xfs_check -n
same as xfs_check
root@ubuntu16-1:~# xfs_repair -n /dev/sdb1
xfs_repair: /dev/sdb1 contains a mounted and writable filesystem
fatal error -- couldn't initialize XFS library
obviously xfs_repair does not work on mounted file system.
root@ubuntu16-1:~# xfs_repair /dev/sdb1
Phase 1 - find and verify superblock...
Phase 2 - using internal log
- zero log...
- scan filesystem freespace and inode maps...
- found root inode chunk
Phase 3 - for each AG...
- scan and clear agi unlinked lists...
- process known inodes and perform inode discovery...
- agno = 0
- agno = 1
- agno = 2
- agno = 3
- process newly discovered inodes...
Phase 4 - check for duplicate blocks...
- setting up duplicate extent list...
- check for inodes claiming duplicate blocks...
- agno = 0
- agno = 1
- agno = 2
- agno = 3
Phase 5 - rebuild AG headers and trees...
- reset superblock...
Phase 6 - check inode connectivity...
- resetting contents of realtime bitmap and summary inodes
- traversing filesystem ...
- traversal finished ...
- moving disconnected inodes to lost+found ...
Phase 7 - verify and correct link counts...
In XFS, you can only extend file system and can not reduce it.

Monitoring free space

On a storage device, a file or directory is contained in a collection of blocks. Information about a file is contained in an inode.
Reminder : inodes keeps information such as who the owner is, when the file was last accessed, how large it is, whether it is a directory, and who can read from or write to it. The inode number is also known as the file serial number and is unique within a particular filesystem.
Data blocks and inodes each take space on a filesystem, so we need to monitor the space usage to ensure that your filesystems have space for growth.


The df (DiskFree) command is used to find out about the free and used space of file systems.
df [OPTION]...[FILE]...
If no file name is passed as an argument with df command then it shows the space available on all currently mounted file systems
root@ubuntu16-1:~# df
Filesystem 1K-blocks Used Available Use% Mounted on
udev 462796 0 462796 0% /dev
tmpfs 98508 6544 91964 7% /run
/dev/sda1 50442940 5613840 42243708 12% /
tmpfs 492540 284 492256 1% /dev/shm
tmpfs 5120 4 5116 1% /run/lock
tmpfs 492540 0 492540 0% /sys/fs/cgroup
tmpfs 98508 48 98460 1% /run/user/1001
-T print file system type, -h, –human-readable print sizes (in power of 1024):
root@ubuntu16-1:~# df -Th
Filesystem Type Size Used Avail Use% Mounted on
udev devtmpfs 452M 0 452M 0% /dev
tmpfs tmpfs 97M 6.4M 90M 7% /run
/dev/sda1 ext4 49G 5.4G 41G 12% /
tmpfs tmpfs 481M 284K 481M 1% /dev/shm
tmpfs tmpfs 5.0M 4.0K 5.0M 1% /run/lock
tmpfs tmpfs 481M 0 481M 0% /sys/fs/cgroup
tmpfs tmpfs 97M 48K 97M 1% /run/user/1001
-H make numbers human readable also (in powers of 1000).
-i list inode information instead of block usage:
root@ubuntu16-1:~# df -i
Filesystem Inodes IUsed IFree IUse% Mounted on
udev 115699 456 115243 1% /dev
tmpfs 123135 750 122385 1% /run
/dev/sda1 3211264 256212 2955052 8% /
tmpfs 123135 9 123126 1% /dev/shm
tmpfs 123135 6 123129 1% /run/lock
tmpfs 123135 17 123118 1% /sys/fs/cgroup
tmpfs 123135 27 123108 1% /run/user/1001
Remember? there is no owner or access rights on vfat filesystems. vfat file format has no inodes!
df command example
df -a
dislpay all information includes pseudo, duplicate and inaccessible file systems.
df -Th /home
Display Information of /home File System
df -k or -m or -h
displays information in Bytes, MB , GB
df -t ext3
include specific file system type
df -x xfs
exclude specific file system type
The df command gives information about a whole filesystem. Sometimes you might want to know how much space is used by a specific file or directory, To answer this kind of question, we use the du command.


The Linux du (Disk Usage) command, used to check the information of disk usage of files and directories on a machine.
du [OPTION]... [FILE]...
useful switch
write count of all files, not just directories
human readable Means we can see sizes in Bytes, KB, MB, GB,...
grand total usage disk space at the last line
go N or fewer sub directories further
display only total for each directory
root@ubuntu16-1:~# du
16 ./.aptitude
8 ./.cache/dconf
12 ./.cache
8 ./.config/htop
8 ./.config/gedit
8 ./.config/dconf
4 ./.config/ibus/bus
8 ./.config/ibus
36 ./.config
4 ./.gnupg/private-keys-v1.d
48 ./.gnupg
4 ./.gconf
12 ./.elinks
16 ./.ssh
4 ./.nano
8 ./.local/share
12 ./.local
336 ./backup
8 ./.dbus/session-bus
12 ./.dbus
4 ./test-space
932 .
root@ubuntu16-1:~# du -sh
932K .
--time option is used to display the last modification time in the output of du.
--exclude=PATTERN will exclude files that match PATTERN example: du -ah --exclude="*.txt" /home/payam


Lets take a look at some other repairing tools beside tools which we have learned in this lesson:
file system
Adjusts parameters on ext2 and ext3 filesystems and can set journaling .
Prints the super block and block group descriptor information for an ext2 or ext3 filesystem.
Is an interactive filesystem debugger. Use it to examine or change the state of an ext2 or ext3 filesystem.
Displays and adjusts parameters on ReiserFS filesystems.
Performs similar functions to dumpe2fs and debugfs for ReiserFS filesystems.
Displays XFS filesystem information.
Expands an XFS filesystem
Changes the parameters of an XFS filesystem.
Repairs an XFS filesystem when the mount checks are not sufficient to repair the system.
Examines or debugs an XFS filesystem.
Displays many aspects of btrfs filesystem information
Check btrfs filesystems
Finds the block that is the root of the btrfs filesystem
Displays btrfs internal metadata
Tune various btrfs filesystem parameters, and enables or disables some extended features
Attempt to restore files from a damaged btrfs filesystem
With the special thanks of shawn powers.