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Syslog message: 'vm_fault: pager read error'

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Article ID: KB36723 KB Last Updated: 03 Apr 2021Version: 1.0
Summary:

This article explains the meaning of the syslog message, 'vm_fault: pager read error' and the corrective action that needs to be taken.

Symptoms:

The affected routing-engine can go offline (status shown as "present" instead of online) with the following syslog messages continuously scrolling on the console: 

​g_vfs_done():md0.uzip[READ(offset=12556288, length=2048)]error = 86
vm_fault: pager read error, pid 1 (init)
g_vfs_done():md0.uzip[READ(offset=12556288, length=2048)]error = 86
vm_fault: pager read error, pid 1 (init)
g_vfs_done():md0.uzip[READ(offset=12556288, length=2048)]error = 86
vm_fault: pager read error, pid 1 (init)
g_vfs_done():md0.uzip[READ(offset=12556288, length=2048)]error = 86
vm_fault: pager read error, pid 1 (init)
g_vfs_done():md0.uzip[READ(offset=12556288, length=2048)]error = 86
vm_fault: pager read error, pid 1 (init)
Cause:

These messages are seen due to kernel read errors. This is related to the underlying FreeBSD based kernel unable to read content from the hard disk and hence can be either the filesystem or kernel issue.

Solution:

In most cases, the RE affected with this error would be stuck in the present state. Having a console session to that RE would allow us to see if it is offline due to the kernel read errors.

To alleviate any file system issue, a file system check (FSCK) needs to be run. This can be done with the help of onsite support who can power off the RE manually and perform a physical reseat, then power it back on.

During the reboot process, the FSCK runs automatically. The logs below show FSCK after it has repaired the filesystem: 

***** FILE SYSTEM MARKED CLEAN *****

***** FILE SYSTEM WAS MODIFIED *****

If read errors continue to appear despite the RE restart, contact your JTAC representative to do an analysis and replace the RE.

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