Eu encontrei duas maneiras de imprimir mensagens de boot usando o dmesg e outro o conteúdo do arquivo /var/log/boot.log:
O conteúdo do arquivo /var/log/boot.log é:
fsck from util-linux 2.20.1
/dev/loop0: clean, 263563/2271232 files, 7843644/18169856 blocks
* Starting configure network device security^[[74G[ OK ]
* Starting configure network device security^[[74G[ OK ]
* Starting configure network device^[[74G[ OK ]
* Starting Mount network filesystems^[[74G[ OK ]
* Starting Failsafe Boot Delay^[[74G[ OK ]
* Stopping Mount network filesystems^[[74G[ OK ]
* Starting Bridge socket events into upstart^[[74G[ OK ]
* Starting mDNS/DNS-SD daemon^[[74G[ OK ]
* Starting Userspace bootsplash^[[74G[ OK ]
* Starting Send an event to indicate plymouth is up^[[74G[ OK ]
* Starting bluetooth daemon^[[74G[ OK ]
* Starting configure network device^[[74G[ OK ]
* Stopping Failsafe Boot Delay^[[74G[ OK ]
* Starting System V initialisation compatibility^[[74G[ OK ]
* Starting set sysctls from /etc/sysctl.conf^[[74G[ OK ]
* Starting configure network device security^[[74G[ OK ]
* Starting modem connection manager^[[74G[ OK ]
* Stopping set sysctls from /etc/sysctl.conf^[[74G[ OK ]
* Starting CUPS printing spooler/server^[[74G[ OK ]
* Starting network connection manager^[[74G[ OK ]
* Stopping cold plug devices^[[74G[ OK ]
* Stopping log initial device creation^[[74G[ OK ]
* Starting configure network device security^[[74G[ OK ]
* Starting save udev log and update rules^[[74G[ OK ]
* Stopping save udev log and update rules^[[74G[ OK ]
* Stopping Userspace bootsplash^[[74G[ OK ]
Skipping profile in /etc/apparmor.d/disable: usr.bin.firefox
Skipping profile in /etc/apparmor.d/disable: usr.sbin.rsyslogd
* Starting AppArmor profiles ^[[170G
^[[164G[ OK ]
speech-dispatcher disabled; edit /etc/default/speech-dispatcher
saned disabled; edit /etc/default/saned
* Stopping System V initialisation compatibility^[[74G[ OK ]
* Starting System V runlevel compatibility^[[74G[ OK ]
enquanto o dmesg dá algo assim:
[ 0.008660] Initializing cgroup subsys blkio
[ 0.008663] Initializing cgroup subsys perf_event
[ 0.008667] Initializing cgroup subsys hugetlb
[ 0.008713] CPU: Physical Processor ID: 0
[ 0.008716] CPU: Processor Core ID: 0
[ 0.008720] mce: CPU supports 4 MCE banks
[ 0.008739] CPU0: Thermal monitoring enabled (TM1)
[ 0.008746] process: using mwait in idle threads
[ 0.008753] Last level iTLB entries: 4KB 64, 2MB 64, 4MB 64
[ 0.008753] Last level dTLB entries: 4KB 64, 2MB 0, 4MB 64
[ 0.008753] tlb_flushall_shift: 6
[ 0.008895] Freeing SMP alternatives: 24k freed
[ 0.011699] ACPI: Core revision 20121018
[ 0.016015] ftrace: allocating 29358 entries in 115 pages
[ 0.028544] ..TIMER: vector=0x30 apic1=0 pin1=2 apic2=-1 pin2=-1
[ 0.068468] smpboot: CPU0: Intel(R) Pentium(R) 4 CPU 3.00GHz (fam: 0f, model: 04, stepping: 09)
[ 0.072000] Performance Events: Netburst events, Netburst P4/Xeon PMU driver.
[ 0.072000] ... version: 0
e assim por diante
Então, minha pergunta como estão os dois relacionados? Quando devemos usar demsg e quando boot.log?
dmesg output são mensagens de diagnóstico do kernel do Linux, ou seja, algumas informações sobre inicialização de hardware e driver.
boot.log parece ser um recurso específico de sua distribuição (não tenho), que mostra um registro de inicializações bem-sucedidas / com falha de seus daemons e outros initscripts localizados em /etc/rc.d/ ou /etc/init.d/ . Esses initscripts são iniciados depois que o kernel do Linux é inicializado.
O dmesg é um buffer de anel de kernels, ele pode ser usado pelo kernel para registrar mensagens antes que os drivers de dispositivos tenham sido carregados (para acessar o disco, etc). boot.log é o armazenamento permanente de mensagens de inicialização.