Booting Mac OS X is attractive and all, but some users would prefer to see what¿s going on behind the scenes. Verbose mode shows you what is really happening during system startup, and is great for troubleshooting. Typically if you wanted to boot in verbose mode you would hit Command-V during startup, which brings up the familiar white on black console. If you'd prefer to always see the system messages on boot, you can adjust the firmware from the Terminal with the nvram command.

To turn on Verbose booting, at a Terminal window

sudo nvram -p |grep boot-args #display current setting (may not be present)
sudo nvram boot-args="-v"
sudo nvram -p |grep boot-args
#display new setting

Disabling Verbose booting sudo nvram boot-args=

If you're curious what the current firmware nvram settings are: as ok El Captian (3/16/16)

> sudo nvram -p
Password:
SystemAudioVolume   W
boot-args   -v
backlight-level %9c%01
boot-gamma  %10%06%00%00%9f%9c%00%00%00%00%00%00%02%01%00%00%00%00%00%00%13%00B%09%1f%00%c3%0f%91%01%85%17%d6%05%87%1d/%0b%89'%8d%17%0d61-%ce:%8d3%d4RmN%1dt%b3p%a4%90%d4%89e%96%0d%92%e8%a1K%9e%aa%a8%b0%a6%ec%b1%9e%b0%ed%b6%a9%b72%ca%d5%cev%d8%fe%dc%fb%ef%ed%f2%be%f9%ff%ff%13%00B%09%1a%00%c3%0fZ%01%85%17%18%05%07%1e4%0a%89'%8f%14%0d6%95'%8f?:2%9aj%b5\%9f}un%a4%90%95~%a8%a3%bb%91%ec%b1k%a1o%bf%d8%b1%f3%ce%d7%c5y%e6%f5%e1%fb%efT%ee%fc%f26%f3%bd%f6%ef%fa%be%f9%ff%ff%14%00B%09%16%00%c3%0f4%01%85%17%8a%04%07%1e%0e%09%89'=%12%0d6%00#%8f?>,%dex%02^%e4%90%c9q%a8%a3%18%80%ad%b6(%920%c3F%9f%b3%ce%8f%acy%e6@%cd%fb%ef|%dc%bd%f4f%e6%bd%f6%cf%ec%bd%f7]%f1%be%f8%df%f7%be%f9%ff%ff
fmm-mobileme-token-FMM  bplist00%d9%01%02%03%04%05%06%07%08%09%0a%0b%16%17%18%19%1a%1b"Vuserid_%10%13dataclassPropertiesYauthTokenXpersonIDXusername_%10%12enabledDataclassesTguidXuserInfo_%10%11osUserDisappeared%11%01%f5%d1%0c%0d_%10!com.apple.Dataclass.DeviceLocator%d4%0e%0f%10%11%12%13%14%15VapsEnvXhostname]authMechanismVschemeZProduction_%10%13p05-fmip.icloud.comUtokenUhttps_%10(AQAAAABT1sk6E2mtHc2vu13GrvYoo0FqcbnktL0~X95670203_%10!dgermanapl@real-world-systems.com%a1%0c_%10$0746C0E4-19BE-4030-9D92-1263CD296B58%d3%1c%1d%1e%1f !_%10%15InUseOwnerDisplayName_%10%13InUseOwnerFirstName_%10%12InUseOwnerLastName]Dennis GermanVDennisVGerman%09%00%08%00%1b%00"%008%00B%00K%00T%00i%00n%00w%00%8b%00%8e%00%91%00%b5%00%be%00%c5%00%ce%00%dc%00%e3%00%ee%01%04%01%0a%01%10%01;%01D%01h%01j%01%91%01%98%01%b0%01%c6%01%db%01%e9%01%f0%01%f7%00%00%00%00%00%00%02%01%00%00%00%00%00%00%00#%00%00%00%00%00%00%00%00%00%00%00%00%00%00%01%f8
bluetoothInternalControllerInfo %13%82%ac%05%00%00%11%06`%fbB%83rH
prev-lang:kbd   en:0
SystemAudioVolumeDB %00
RemoteDisabled  %01
fmm-computer-name   smackerpro
efi-boot-device IOMatchIOProviderClassIOMediaIOPropertyMatchUUID8184AD94-2146-4A57-A1EB-A81B5BE61F44BLLastBSDNamedisk0s2%00
bluetoothActiveControllerInfo   %13%82%ac%05%00%00%00%00%11%06`%fbB%83rH
efi-boot-device-data    %02%01%0c%00%d0A%03%0a%00%00%00%00%01%01%06%00%00%0b%03%12%0a%00%00%00%00%00%00%00%04%01*%00%02%00%00%00(@%06%00%00%00%00%00x%9b%d9%05%00%00%00%00%94%ad%84%81F!WJ%a1%eb%a8%1b[%e6%1fD%02%02%7f%ff%04%00
csr-active-config   w%00%00%00
LocationServicesEnabled %01


aka:
SystemAudioVolume   W
boot-args   -v
backlight-level  9c 01
boot-gamma   10 06 00 00 9f 9c 00   00 00 00 00 00 02 01 00
             00 00 00 00 00 13 30   0B 09 1f 00 c3 0f 91 01
             85 17 d6 05 87 1d  /   0b 89  ' 8d 17 0d 61  - 
             ce  :  8 d3 d4RmN 1dt b3p a4 90 d4 89e 96 0d 92
 e8 a1K 9e aa a8 b0 a6 ec b1 9e b0 ed b6 a9 b72 ca d5 cev d8
 fe dc fb ef ed f2 be f9 ff ff 13 00B 09 1a 00 c3 0fZ 01 85
 17 18 05 07 1e4 0a 89' 8f 14 0d6 95'8f?:2 9aj b5\ 9f}un a4 
90 95~ a8 a3 bb 91 ec b1k a1o bf d8 b1 f3 ce d7 c5y e6 f5 e1 
fb efT ee fc f26 f3 bd f6 ef fa be f9 ff ff 14 00B 09 16 00 
c3 0f4 01 85 17 8a 04 07 1e 0e 09 89'= 12 0d6 00# 8f?>, 
dex 02^ e4 90 c9q a8 a3 18 80 ad b6( 920 c3F 9f b3 ce 8f 
acy e6@ cd fb ef| dc bd f4f e6 bd f6 cf ec bd f7] f1 be f8 df f7 be f9 ff ff

fmm-mobileme-token-FMM  bplist00 d9 01 02 03 04 05 06 07 08 09 0a 0b 16 17 18 19 1a 1b"V
userid_ 10 13
dataclassPropertiesYauthTokenXpersonI  DX
username_ 10 12
enabledDataclassesTguidXuserInfo_ 10 11os
UserDisappeared 11 01 f5 d1 0c 0d_ 10!
com.apple.Dataclass.DeviceLocator d4 0e 0f 10 11 12 13 14 15V
apsEnvXhostname]authMechanismVschemeZProduction_ 10 13p05-f
mip.icloud.comUtokenUhttps_ 10(AQAAAABT1sk6E2mtHc2vu13GrvYoo0FqcbnktL0~X95670203_ 10!
dgermanapl@real-world-systems.com a1 0c_ 10$0746C0E4-19BE-4030-9D92-1263CD296B58 d3 1c 1d 1e 1f !_ 10 15
InUseOwnerDisplayName_ 10 13
InUseOwnerFirstName_ 10 12
InUseOwnerLastName]DennisGermanVDennisVGerman 09 00 08 00 1b 00" 008 00B 00K 00T 00i 00n 00w 00 8b 00 8e 
   00 91 00 b5 00 be 00 c5 00 ce 00 dc 00 e3 00 ee 01 04 01 0a 01 10 01;01D
 01h 01j 01 91 01 98 01 b0 01 c6 01 db 01 e9 01 f0 01 f7 00 00 00 00 00 00 
02 01 00 00 00 00 00 00 00# 00 00 00 00 00 00 00 00 00 00 00 00 00 00 01 f8
bluetoothInternalControllerInfo  13 82 ac 05 00 00 11 06` fbB 83rH
prev-lang:kbd   en:0
SystemAudioVolumeDB  00
RemoteDisabled   01
fmm-computer-name   smackerpro
efi-boot-device 
        IOMatch
        IOProviderClassIOMedia
        IOPropertyMatch
            UUID8184AD94-2146-4A57-A1EB-A81B5BE61F44 
      
        BLLastBSDNamedisk0s2 00
bluetoothActiveControllerInfo    13 82 ac 05 00 00 00 00 11 06` fbB 83rH
efi-boot-device-data     02 01 0c 00 d0A 03 0a 00 00 00 00 01 01
     06 00 00 0b 03 12 0a 00 00 00 00 00 00 00 04 01* 00 
    02 00 00 00(@ 06 00 00 00 00 00x 9b d9 05 00 00 00 00 94 ad 84 
    81F!WJ a1 eb a8 1b[ e6 1fD 02 02 7f ff 04 00
csr-active-config   w 00 00 00
LocationServicesEnabled  01

sudo nvram -p
nvramrc	
scroll-lock	true
boot-command	mac-boot
pci-probe-mask	-1
skip-netboot?	false
default-client-ip	
default-subnet-mask	
default-gateway-ip	
default-server-ip	
default-router-ip	
diag-device	enet
default-mac-address?	false    
boot-device	pci2/ata-6@D/@0:3,\\:tbxi    
real-size	-1
logger-size	-1
auto-boot?	true
use-generic?	false

boot-volume	3
logger-base	-1
little-endian?	false
selftest-#megs	0
ram-size	0x50000000  
output-device	screen
virt-base	-1
boot-file	
boot-script	
use-nvramrc?	false
boot-screen	screen
screen-#rows	40
screen-#columns	100
console-screen	screen
input-device	keyboard
real-base	-1
mouse-device	mouse
oem-banner?	false
oem-banner	
fcode-debug?	false
real-mode?	false
aapl,tdm-units	
virt-size	-1
diag-file	,diags
load-base	0x800000
output-device-1	scca
diag-switch?	false
gmt-offset	0
input-device-1	scca
oem-logo	
oem-logo?	false
boot-args	

aapl,pci	/@f0000000/@10%00MVAD%00\%01%82%ff%81?%ff%81%0e%ba%0c%07%82%ff%01%07%17%ff%018%19d%04%ff%01%05@%ff%01%18%ff%01%88%03%ff%01%03&%ff%01%03%ff%01%06%03%ff%01%04%ff%03%19d%04%ff%01%05@%ff%01%08%ff%01 %03%ff%01%03&%ff%01%01%ff%01%02%03%ff%01%04%ff%01<%ff%05%00
platform-uuid	%00%00%00%00%00%00%10%00%80%00%00%11$G?%aa

nvram - manipulate Open Firmware NVRAM variables

nvram [ -p ] [ -f filename ] [ -d name ] [ name [= value ]] ...

manipulates of Open Firmware NVRAM variables. It can be used to get or set a variable. It can also be used to print all of the variables or set a list of variables from a file. Changes to NVRAM variables are only saved by clean restart or shutdown. In principle, name can be any string. In practice, not all strings will be accepted. New World machines can create new variables as desired. Some variables require administrator privilege to get or set. The value must match the data type required for name. Binary data can be set using the %xx notation, where xx is the hex value of the byte. The type for new variables is always binary data.
-p Print all of the Open Firmware variables.
-f filename Set Open Firmware variables list, name=value statements from a text file. If the last character of a line is \, the value will be continued to the next line.
-d name Deletes the named Open Firmware variable.
-x use XML format. (preceed -f or -p)
EXAMPLES

> nvram boot-args="-s rd=*hd:10"

Set the boot-args variable to "-s rd=*hd:10". This would specify single user mode with the root device in hard drive partition 10.

> nvram my-variable="String One%00String Two%00%00"

Create a new variable, my-variable, containing a list of two C-strings that is terminated by a NUL.

> nvram -d my-variable

Deletes the variable named my-variable.

October 28, 2003