Interpreting dmesg Output: Drive Failure Imminent
As a sysadmin, it's crucial to be able to interpret system logs to identify and address potential issues before they become critical. One such issue is drive failure, which can be detected through the dmesg command. In this article, we'll cover how to interpret the dmesg output to identify a drive failure and what steps to take to prevent data loss.
Understanding the dmesg command
dmesg is a command that displays the kernel ring buffer, which contains messages from the kernel and drivers. It's a powerful tool for troubleshooting system issues, as it provides detailed information about system events, including hardware and software errors. In the context of drive failure, the dmesg output can provide critical information about the state of the drive and any errors that have occurred.
Interpreting the dmesg output for drive failure
In the example provided, the dmesg output indicates that there is a problem with the drive connected to the ata5 interface:
[Fri Feb 16 16:15:48 2024] ata5.00: exception Emask 0x10 SAct 0x20000 SErr 0x2cThe Emask value indicates the type of error that has occurred. In this case, the value 0x10 indicates that there is a problem with the device's I/O operations. The SAct value provides information about the device's state, and the SErr value indicates the specific error that has occurred.
To identify the device in question, you can use the lsblk command:
$ lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
sda 8:0 0 931.5G 0 disk
├─sda1 8:1 0 512M 0 part /boot/efi
├─sda2 8:2 0 16G 0 part [SWAP]
└─sda3 8:3 0 914.9G 0 part /
sdb 8:16 0 1919.4G 0 disk
├─sdb1 8:17 0 1G 0 part /boot
└─sdb2 8:18 0 1.9T 0 part /dataBased on the dmesg output, we can see that the device in question is /dev/sdb, which is a 2TB drive. The fact that the error occurred on ata5 suggests that this drive is connected to the fifth SATA port on the motherboard.
Preventing data loss
If you suspect that a drive is failing, it's important to take action immediately to prevent data loss. Here are some steps you can take:
- Backup your data: The most important step is to ensure that your data is backed up. If the drive fails completely, you'll need to be able to recover your data from a backup.
- Check the S.M.A.R.T. status: S.M.A.R.T. (Self-Monitoring, Analysis and Reporting Technology) is a feature built into most modern hard drives that can provide information about the drive's health. You can use a tool like
smartctlto check the S.M.A.R.T. status of the drive:$ sudo smartctl -a /dev/sdb smartctl 7.1 2019-12-30 r5073 [x86_64-linux-5.4.0-90-generic] (local build) Copyright (C) 2002-19, Bruce Allen, Christian Franke, www.smartmontools.org === START OF INFORMATION SECTION === Model Family: Western Digital Red Device Model: WDC WD20EFRX-68AX9N0 Serial Number: WD-WCC4T0897637 LU WWN Device Id: 5 0014ee 24e2a3c9f Firmware Version: 80.00A80 User Capacity: 2,000,398,934,016 bytes [2.00 TB] Sector Size: 512 bytes logical/physical Rotation Rate: 5400 rpm Form Factor: 3.5 inches Device is: In smartctl database [for details use: -P show] ATA Version is: 8 ATA Standard is: Exact ATA specification version not given Local Time is: Sat Feb 18 10:18:25 2023 EST SMART support is: Available - device has SMART capability. SMART support is: Enabled === START OF READ SMART DATA SECTION === SMART overall-health self-assessment test result: PASSED General SMART Values: Offline data collection status: (0x82) Offline data collection activity was completed without error. Auto Offline Data Collection: Enabled. Self-test execution status: ( 0) The previous self-test routine completed without error or no self-test has ever been run. Total time to complete Offline data collection: ( 120) seconds. Offline data collection capabilities: (0x5b) SMART execute Offline immediate. Auto Offline data collection on/off support. Suspend Offline collection upon new command. Offline surface scan supported. Self-test supported. Conveyance Self-test supported. Selective Self-test supported. SMART capabilities: (0x0003) Saves SMART data before entering power-saving mode. Supports SMART auto save timer. Error logging capability: (0x01) Error logging supported. General Purpose Logging supported. Short self-test routine recommended polling time: ( 1) minutes. Extended self-test routine recommended polling time: ( 217) minutes. Conveyance self-test routine recommended polling time: ( 2) minutes. SCT capabilities: (0x003d) SCT Status supported. SCT Feature Control supported. SCT Data Table supported. SMART Attributes Data Structure revision number: 16 Vendor Specific SMART Attributes with Thresholds: ID# ATTRIBUTE_NAME FLAG VALUE WORST THRESH TYPE UPDATED WHEN_FAILED RAW_VALUE 1 Raw_Read_Error_Rate 0x000b 100 100 016 Pre-fail Always - 0 2 Throughput_Performance 0x0005 100 100 054 Pre-fail Offline - 0 3 Spin_Up_Time 0x0027 100 100 024 Pre-fail Always - 0 4 Start_Stop_Count 0x0032 100 100 000 Old_age Always - 16 5 Reallocated_Sector_Ct 0x0033 100 100 005 Pre-fail Always - 0 7 Seek_Error_Rate 0x000b 100 100 067 Pre-fail Always - 0 8 Seek_Time_Performance 0x0005 100 100 020 Pre-fail Offline - 0 9 Power_On_Hours 0x0032 097 097 000 Old_age Always - 13652 10 Spin_Retry_Count 0x0033 198 100 030 Pre-fail Always - 0 12 Power_Cycle_Count 0x0032 100 100 000 Old_age Always - 16 192 Power-Off_Retract_Count 0x0032 100 100 000 Old_age Always - 31 193 Load_Cycle_Count 0x0032 100 100 000 Old_age Always - 31 194 Temperature_Celsius 0x0022 114 114 000 Old_age Always - 31 196 Reallocated_Event_Count 0x0032 100 100 000 Old_age Always - 0 197 Current_Pending_Sector 0x0032 100 100 000 Old_age Always - 0 198 Offline_Uncorrectable 0x0030 100 100 000 Old_age Offline - 0 199 UDMA_CRC_Error_Count 0x0032 200 200 000 Old_age Always - 0 ...In this example, the S.M.A.R.T. status is
PASSED, which is a good sign. However, if the status isFAILED, it's a strong indication that the drive is failing and should be replaced as soon as possible. - Replace the drive: If the S.M.A.R.T. status indicates that the drive is failing, or if you're seeing errors in the
dmesgoutput, it's time to replace the drive. Make sure to backup any critical data before doing so, and consider using a tool likeddrescueto create a sector-by-sector copy of the drive to ensure that you're able to recover as much data as possible.
Interpreting the dmesg output is a critical skill for sysadmins, as it can provide early warning of drive failure and other system issues. By understanding the different components of the dmesg output and how to interpret them, you can take action to prevent data loss and keep your systems running smoothly.