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[Junos] FSCK inconsistencies/errors seen when running Junos OS on a live mounted filesystem

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Article ID: KB35902 KB Last Updated: 16 Jul 2020Version: 1.0
Summary:

This article describes the FSCK inconsistencies/errors that are seen when running Junos OS on a live mounted filesystem, and indicates the recommended method for checking the consistency of a Junos OS filesystem.

Note: This article is not applicable to Junos OS Evolved​.

 

Symptoms:

When you run fsck on a mounted Junos OS device, you will see several known false positive messages (that is, the unreferenced files) as shown below.

Check the following logs:

root@Juniper> start shell 
root@Juniper:RE:0% fsck
** /dev/da0s1a (NO WRITE)          >> “NO WRITE” indicates that FSCK is being run on a live filesystem and can’t make changes.
** Last Mounted on /instrootmnt
** Root file system
** Phase 1 - Check Blocks and Sizes
** Phase 2 - Check Pathnames
** Phase 3 - Check Connectivity
** Phase 4 - Check Reference Counts
** Phase 5 - Check Cyl groups
2404 files, 98507 used, 63430 free (22 frags, 7926 blocks, 0.0% fragmentation)
** /dev/da0s4d (NO WRITE)
** Last Mounted on /config
** Phase 1 - Check Blocks and Sizes
** Phase 2 - Check Pathnames
** Phase 3 - Check Connectivity
** Phase 4 - Check Reference Counts
** Phase 5 - Check Cyl groups
43 files, 50 used, 59096 free (24 frags, 7384 blocks, 0.0% fragmentation)
** /dev/da0s3e (NO WRITE)
** Last Mounted on /var
** Phase 1 - Check Blocks and Sizes
** Phase 2 - Check Pathnames
** Phase 3 - Check Connectivity
** Phase 4 - Check Reference Counts
UNREF FILE  I=5675  OWNER=root MODE=140600
SIZE=0 MTIME=May 28 12:13 2020 
RECONNECT? no

CLEAR? no

UNREF FILE  I=5693  OWNER=root MODE=140600
SIZE=0 MTIME=May 28 12:13 2020 
RECONNECT? no

CLEAR? no

** Phase 5 - Check Cyl groups
552 files, 9556 used, 77320 free (216 frags, 9638 blocks, 0.2% fragmentation)
** /dev/da0s3d (NO WRITE)
** Last Mounted on /var/tmp
** Phase 1 - Check Blocks and Sizes
** Phase 2 - Check Pathnames
** Phase 3 - Check Connectivity
** Phase 4 - Check Reference Counts
** Phase 5 - Check Cyl groups
13 files, 40481 used, 413874 free (34 frags, 51730 blocks, 0.0% fragmentation)
root@Juniper:RE:0% 

In the above output, FSCK found an UNREF FILE when it was run on a mounted device running Junos OS. Similarly, users may see unallocated blocks/fragments, unreferenced files, wrong link counts, directory mismatches, inconsistent summary table/cylinder group summaries, and other such “errors”.

 

Cause:

There is no standard method for checking the consistency of a live mounted filesystem (that is running Junos OS) and FSCK, when run on a live mounted filesystem, will give several errors such as the above that are not actual corruptions but false positives that can be ignored.

 

Solution:

The only way to check the consistency of a filesystem is to reboot and let the system check it while booting up. However, if the filesystems are unmounted cleanly by the reboot, they are typically not checked.

This could therefore be used as evidence that the error messages seen in FSCK on the mounted filesystem are just false positives and that there is no real issue with filesystem consistency. The false positives can be ignored.

 

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