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DMESG FreeBSD

 ·  🎃 kr0m

The output of the dmesg command in FreeBSD isn’t very user-friendly. Additionally, it has a significant limitation: we can’t determine the exact time each event was recorded. In this tutorial, we’ll work around this by enabling timestamps and converting them to human-readable dates.

In the Linux version of dmesg, at least we have the -T parameter to view dates directly, but in FreeBSD, this parameter simply doesn’t exist:

dmesg -T  
dmesg: illegal option -- T  
usage: dmesg [-ac] [-M core [-N system]]

First, we need to enable timestamp logging at the kernel level:

echo 'kern.msgbuf_show_timestamp=1' >> /etc/sysctl.conf  
sysctl kern.msgbuf_show_timestamp=1  

kern.msgbuf_show_timestamp: 0 -> 1

And reboot:

shutdown -r now

The timestamps will appear as seconds since system boot:

[30] CPU: Intel(R) Core(TM)2 Duo CPU     P9500  @ 2.53GHz (2533.32-MHz K8-class CPU)  
[30]   Origin="GenuineIntel"  Id=0x10676  Family=0x6  Model=0x17  Stepping=6  
[30]   Features=0xbfebfbff<FPU,VME,DE,PSE,TSC,MSR,PAE,MCE,CX8,APIC,SEP,MTRR,PGE,MCA,CMOV,PAT,PSE36,CLFLUSH,DTS,ACPI,MMX,FXSR,SSE,SSE2,SS,HTT,TM,PBE>  
[30]   Features2=0x8e3fd<SSE3,DTES64,MON,DS_CPL,VMX,SMX,EST,TM2,SSSE3,CX16,xTPR,PDCM,SSE4.1>  
[30]   AMD Features=0x20100800<SYSCALL,NX,LM>  
[30]   AMD Features2=0x1<LAHF>  
[30]   VT-x: HLT,PAUSE  
[30]   TSC: P-state invariant, performance statistics  
[30] wlan0: Ethernet address: 00:22:5f:62:3e:68  
[30] nfe0: link state changed to UP  
[30] lo1: changing name to 'bastille0'  
[30] lo0: link state changed to UP  
[30] nfe0: link state changed to DOWN  
[31] pflog0: promiscuous mode enabled  
[32] Security policy loaded: MAC/ntpd (mac_ntpd)  
[33] nfe0: link state changed to UP

To convert the timestamps to human-readable dates, we’ll use the following script, which depends on ccze. Let’s install it first:

pkg install ccze  

vi .scripts/dmesg-human.sh  

#!/bin/sh  

# Get system boot time (Unix timestamp)  
boot_time=$(sysctl -n kern.boottime | awk '{print $4}' | tr -d ',')  

# Process dmesg output  
dmesg | awk -v bt="$boot_time" '  
    # Preserve boot headers and copyright lines unchanged  
    /^---<<BOOT>>---/ || /^Copyright/ || /^FreeBSD/ { print; next }  

    # Convert timestamped lines (e.g., "[8] message")  
    /^\[[0-9]+\]/ {  
        gsub(/\[|\]/, "", $1);  # Remove brackets from timestamp  
        ts = $1;                # Extract timestamp  
        $1 = "";               # Remove timestamp from line  
        # Convert to human-readable time  
        cmd = "date -j -f %s " (bt + ts) " \"+%Y-%m-%d %H:%M:%S\" 2>/dev/null"  
        cmd | getline human_time  
        close(cmd)  
        printf "[%s]%s\n", human_time, $0  
        next  
    }  

    # Print all other lines as-is  
    { print }  
' | ccze -A

Set the necessary permissions:

chmod 700 .scripts/dmesg-human.sh

When we run the script, we’ll see much more user-friendly output:

.scripts/dmesg-human.sh
DMESG DMESG-Script

See Also