dmesg: System Message Buffer

dmesg provides a quick way to get status updates and hardware information:

$ dmesg
OpenBSD 7.4 (GENERIC.MP) #1397: Tue Oct 10 09:02:37 MDT 2023
    deraadt@amd64.openbsd.org:/usr/src/sys/arch/amd64/compile/GENERIC.MP
real mem = 51486306304 (49101MB)
avail mem = 49906188288 (47594MB)
random: good seed from bootblocks
mpath0 at root
scsibus0 at mpath0: 256 targets
mainbus0 at root
bios0 at mainbus0: SMBIOS rev. 2.7 @ 0xec830 (156 entries)
bios0: vendor American Megatrends Inc. version "3.3" date 05/23/2018
bios0: Supermicro X9DRi-LN4+/X9DR3-LN4+
acpi0 at bios0: ACPI 4.0
acpi0: sleep states S0 S1 S4 S5
acpi0: tables DSDT FACP APIC FPDT SRAT SLIT HPET PRAD SPMI SSDT EINJ ERST HEST BERT DMAR MCFG
acpi0: wakeup devices P0P9(S1) EUSB(S4) USBE(S4) PEX0(S4) PWVE(S4) NPE1(S4) NPE4(S4) NPE5(S4) NPE6(S4) NPE8(S4) NPEA(S4) NPE2(S4) NPE3(S4) NPE7(S4) NPE9(S4) NPE2(S4) [...]
acpitimer0 at acpi0: 3579545 Hz, 24 bits
acpimadt0 at acpi0 addr 0xfee00000: PC-AT compat
cpu0 at mainbus0: apid 0 (boot processor)
cpu0: Intel(R) Xeon(R) CPU E5-2620 0 @ 2.00GHz, 2000.07 MHz, 06-2d-07, patch 0000071a
cpu0: FPU,VME,DE,PSE,TSC,MSR,PAE,MCE,CX8,APIC,SEP,MTRR,PGE,MCA,CMOV,PAT,PSE36,CFLUSH,DS,ACPI,MMX,FXSR,SSE,SSE2,SS,HTT,TM,PBE,SSE3,PCLMUL,DTES64,MWAIT,DS-CPL,VMX,SMX,EST,TM2,SSSE3,CX16,xTPR,PDCM,PCID,DCA,SSE4.1,SSE4.2,x2APIC,POPCNT,DEADLINE,AES,XSAVE,AVX,NXE,PAGE1GB,RDTSCP,LONG,LAHF,PERF,ITSC,MD_CLEAR,IBRS,IBPB,STIBP,L1DF,SSBD,SENSOR,ARAT,XSAVEOPT,MELTDOWN
cpu0: 32KB 64b/line 8-way D-cache, 32KB 64b/line 8-way I-cache, 256KB 64b/line 8-way L2 cache, 15MB 64b/line 20-way L3 cache
cpu0: smt 0, core 0, package 0
mtrr: Pentium Pro MTRR support, 10 var ranges, 88 fixed ranges
cpu0: apic clock running at 100MHz
cpu0: mwait min=64, max=64, C-substates=0.2.1.1.2, IBE
...

As you can see from above, dmesg provides us with information about the OpenBSD kernel (OpenBSD 7.4 (GENERIC.MP)), the amount of real memory on the system, and the number and type of processors. Although not shown here, dmesg also provides information about storage disks and peripherals.

Sometimes, status messages may fill up the dmesg buffer. When that occurs, view /var/run/dmesg.boot for a copy of dmesg saved at boot time.

For example, to view the disks on the current system:

$ dmesg | grep -E '(sd|wd)[0-9]'
sd0 at scsibus1 targ 0 lun 0: <VirtIO, Block Device, >
sd0: 20480MB, 512 bytes/sector, 41943040 sectors
sd1 at scsibus2 targ 0 lun 0: <VirtIO, Block Device, >
sd1: 256000MB, 512 bytes/sector, 524288000 sectors