Monday, December 17, 2012

EXT3-fs warning: checktime reached, running e2fsck is recommended

From Linux syslog[1] (i.e., /var/log/messages), we have found the following message:
  • EXT3-fs warning: checktime reached, running e2fsck is recommended 

And, from the file system disk space report (i.e., "df -k"), we find:

Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/sda3             61189192  31629588  26401228  55% /
/dev/sda1               101086     21650     74217  23% /boot
tmpfs                 16472072         0  16472072   0% /dev/shm
/dev/sdb              70440240  35203348  31658524  53% /data

So, our Linux platform has three different file systems:
  • /dev/sda1
  • /dev/sda3
  • /dev/sdb

What is /dev/sda1[2,5]?


For Linix device naming,

  • hd
    • It designates IDE devices
  • sd
    • It designates SCSI devices including kernel-level emulation of SCSI devices, like USB devices or, in some cases, CD-RW drives.

The a and the b's, etc .. (i.e., sda, sdb)are the equivalent to the concept of hda, and hdb, etc.  When different devices are plugged in, they are mapped to sda, sdb, etc. For detailed information about these plug-in devices, we can find them in the boot message, which can be generated by:
  • $dmesg > boot.messages
From the boot message, we have found the following entries:


scsi0 : aacraid
  Vendor: Sun       Model: ssssss-xdddd-dd   Rev: V1.0
  Type:   Direct-Access                      ANSI SCSI revision: 02
SCSI device sda: 143134720 512-byte hdwr sectors (73285 MB)
sda: Write Protect is off
sda: Mode Sense: 06 00 10 00
SCSI device sda: drive cache: write through w/ FUA
SCSI device sda: 143134720 512-byte hdwr sectors (73285 MB)
sda: Write Protect is off
sda: Mode Sense: 06 00 10 00
SCSI device sda: drive cache: write through w/ FUA
 sda: sda1 sda2 sda3
sd 0:0:0:0: Attached scsi removable disk sda
  Vendor: Sun       Model: solaris root      Rev: V1.0
  Type:   Direct-Access                      ANSI SCSI revision: 02
 .
 .
 .

EXT3 FS on sda3, internal journal
kjournald starting.  Commit interval 5 seconds
EXT3 FS on sda1, internal journal
EXT3-fs: mounted filesystem with ordered data mode.
kjournald starting.  Commit interval 5 seconds
EXT3-fs warning: checktime reached, running e2fsck is recommended
EXT3 FS on sdb, internal journal
EXT3-fs: mounted filesystem with ordered data mode.
Adding 8289532k swap on /dev/sda2.  Priority:-1 extents:1 across:8289532k

So, we know our devices use EXT3 FS.

What Is EXT3 FS[3]?


EXT3 FS, or third extended filesystem, is a journaled file system that is commonly used by the Linux kernel.  It is the default file system for many popular Linux distributions.

EXT3 adds the following features to EXT2:
  • A journal
  • Online file system growth
  • Htree indexing for larger directories
Without these features, any EXT3 file system is also a valid EXT2 file system. This situation has allowed well-tested and mature file system maintenance utilities for maintaining and repairing EXT2 file systems to also be used with EXT3 without major changes. The EXT2 and EXT3 file systems share the same standard set of utilities, e2fsprogs, which includes an fsck tool. The close relationship also makes conversion between the two file systems (both forward to EXT3 and backward to EXT2) straightforward.

With all these background information, now we are ready to run e2fsck as recommended.

Running e2fsck


In general it is not safe to run e2fsck on mounted filesystems. So, before we run e2fsck command, we have unmounted our file system.


[root@myserver bench]# umount -v /dev/sdb
/dev/sdb umounted
[root@myserver bench]# /sbin/e2fsck -v  /dev/sdb
e2fsck 1.39 (29-May-2006)
data has gone 652 days without being checked, check forced.
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

  349958 inodes used (3.90%)
    2278 non-contiguous inodes (0.7%)
         # of inodes with ind/dind/tind blocks: 16016/1145/0
 9082105 blocks used (50.76%)
       0 bad blocks
       2 large files

  311040 regular files
   38016 directories
       0 character device files
       0 block device files
       0 fifos
       0 links
     893 symbolic links (893 fast symbolic links)
       0 sockets
--------
  349949 files


/etc/fstab[4]


The 6th column of fstab is a fsck option. fsck looks at the number in the 6th column to determine in which order the filesystems should be checked. If it's zero, fsck won't check the filesystem.

In our system, we find that both "/" and "/boot" filesystems are automatically checked whenever the system is rebooted:
LABEL=/                 /                       ext3    defaults        1 1
LABEL=/boot             /boot                   ext3    defaults        1 2
Therefore, we don't need to fsck either /dev/sda3 or /dev/sda1.

References

  1. Troubleshooting Linux with syslog
  2. What is /dev/sda1?
  3. ext3 (Wikipedia)
  4. How to edit and understand /etc/fstab - 1.1
  5. linux sda vs hda ?

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