数据库管理员在数据库的运维过程中或多或少要和操作系统乃至硬件打上交道，分析数据库故障时操作系统日志往往也是一个重要的线索来源。 以Linux操作系统为例，其主要的日志子系统(syslog subsystem)可大致分为三类：即1)用户连接日志 2)进程统计日志 3)系统和服务日志。 前2种在我们进行系统的安全审计及用户监控时可以派上用场，而因操作系统或硬件问题造成的数据库故障，我们往往需要关注系统和服务日志。在Linux上我们最常分析的是/var/log/messages日志文件，该日志文件包含了系统和服务的info信息(除mail,cron等服务外),这里我们要介绍的是/var/log/dmesg日志文件，该日志文件描述了系统开机时BIOS硬件加载成功与否的信息，以及网卡、光驱、软驱驱动和RAID、LVM、IPv6等的配置信息。此日志文件的信息记录存放在内核缓存中，主要用于硬件信息故障检测。用户既可以使用cat /var/log/dmesg命令来查看该日志信息，也直接可以使用dmesg命令来查看该日志信息。如：
[root@nas ~]# dmesg |egrep "sd|eth" SCSI device sda: 625142448 512-byte hdwr sectors (320073 MB) sda: Write Protect is off sda: Mode Sense: 00 3a 00 00 SCSI device sda: drive cache: write back SCSI device sda: 625142448 512-byte hdwr sectors (320073 MB) sda: Write Protect is off sda: Mode Sense: 00 3a 00 00 SCSI device sda: drive cache: write back sda: sda1 sda2 sda3 sda4 sd 0:0:0:0: Attached scsi disk sda eth0: RTL8168d/8111d at 0xffffc20000032000, b8:ac:6f:dc:8b:43, XID 081000c0 IRQ 50 sd 0:0:0:0: Attached scsi generic sg0 type 0 SCSI device sdb: 976773168 512-byte hdwr sectors (500108 MB) sdb: Write Protect is off sdb: Mode Sense: 10 00 00 00 sdb: assuming drive cache: write through SCSI device sdb: 976773168 512-byte hdwr sectors (500108 MB) sdb: Write Protect is off sdb: Mode Sense: 10 00 00 00 sdb: assuming drive cache: write through sdb: sdb1 sdb2 sd 2:0:0:0: Attached scsi disk sdb sd 2:0:0:0: Attached scsi generic sg2 type 0 EXT3 FS on sda1, internal journal EXT3 FS on sda2, internal journal Adding 5116692k swap on /dev/sda3. Priority:-1 extents:1 across:5116692k r8169: eth0: link up r8169: eth0: link up eth0: no IPv6 routers present /* 以上列出了系统识别的scsi硬盘及网卡的信息*/ [root@nas ~]# cat /var/log/messages |grep -i fail Jan 17 03:04:03 nas udevd-event[2943]: wait_for_sysfs: waiting for '/sys/devices/pci0000:00/0000:00:1d.7/usb2/2-1/2-1:1.0/host3/target3:0:0/3:0:0:0/ioerr_cnt' failed Jan 18 04:45:08 nas udevd-event[5138]: wait_for_sysfs: waiting for '/sys/devices/pci0000:00/0000:00:1d.7/usb2/2-1/2-1:1.0/host8/target8:0:0/8:0:0:0/ioerr_cnt' failed Jan 18 04:45:08 nas kernel: sdb : READ CAPACITY failed. Jan 18 04:45:08 nas kernel: sdb : READ CAPACITY failed. /* 以上列出了硬件检测失败记录 */ [root@nas ~]# dmesg |grep -i err ACPI: IRQ0 used by override. ACPI: IRQ2 used by override. ACPI: IRQ9 used by override. Using local APIC timer interrupts. ACPI: Using IOAPIC for interrupt routing ACPI: PCI Interrupt Routing Table [\_SB_.PCI0._PRT] ACPI: PCI Interrupt Routing Table [\_SB_.PCI0.P0P1._PRT] ACPI: PCI Interrupt Routing Table [\_SB_.PCI0.P0P4._PRT] ACPI: PCI Interrupt Routing Table [\_SB_.PCI0.P0P6._PRT] ACPI: PCI Interrupt Link [LNKA] (IRQs 3 4 6 7 10 *11 12 14 15) ACPI: PCI Interrupt Link [LNKB] (IRQs *5) ACPI: PCI Interrupt Link [LNKC] (IRQs 3 4 6 7 *10 11 12 14 15) ACPI: PCI Interrupt Link [LNKD] (IRQs 3 4 6 7 10 11 12 14 *15) ACPI: PCI Interrupt Link [LNKE] (IRQs 3 4 6 7 10 11 12 14 15) *0, disabled. ACPI: PCI Interrupt Link [LNKF] (IRQs 3 4 6 7 10 11 12 *14 15) ACPI: PCI Interrupt Link [LNKG] (IRQs *3 4 6 7 10 11 12 14 15) ACPI: PCI Interrupt Link [LNKH] (IRQs 3 4 6 *7 10 11 12 14 15) ACPI: PCI Interrupt 0000:00:1c.0[A] -> GSI 17 (level, low) -> IRQ 169 ACPI: PCI Interrupt 0000:00:1c.2[C] -> GSI 18 (level, low) -> IRQ 177 ide: Assuming 33MHz system bus speed for PIO modes; override with idebus=xx ACPI: PCI Interrupt 0000:00:1a.7[C] -> GSI 18 (level, low) -> IRQ 177 ACPI: PCI Interrupt 0000:00:1d.7[A] -> GSI 23 (level, low) -> IRQ 209 ACPI: PCI Interrupt 0000:00:1a.0[A] -> GSI 16 (level, low) -> IRQ 217 ACPI: PCI Interrupt 0000:00:1a.1[B] -> GSI 21 (level, low) -> IRQ 225 ACPI: PCI Interrupt 0000:00:1d.0[A] -> GSI 23 (level, low) -> IRQ 209 ACPI: PCI Interrupt 0000:00:1d.1[B] -> GSI 19 (level, low) -> IRQ 233 ACPI: PCI Interrupt 0000:00:1d.2[C] -> GSI 18 (level, low) -> IRQ 177 ACPI: PCI Interrupt 0000:00:1f.2[B] -> GSI 19 (level, low) -> IRQ 233 ACPI: PCI Interrupt 0000:00:1f.3[C] -> GSI 18 (level, low) -> IRQ 177 ACPI: PCI Interrupt 0000:02:00.0[A] -> GSI 18 (level, low) -> IRQ 177 ACPI: PCI Interrupt 0000:00:1b.0[A] -> GSI 22 (level, low) -> IRQ 58 /* 以上列出了硬件检测错误记录 */
/var/log/dmesg硬件检测日志的格式较为简单，一般为"device name:message text"的形式。该日志中常见的设备名称有:SCSI,PCI,Memory,loop,Kernel,EXT3,DMA,CPU,Console,BIOS,ata2,ata1,ACPI,floppy,Time等。其中ACPI(Advanced Configuration and Power Interface)即高级电源管理服务，可以看到以上日志中该服务的PCI中断出现了某些问题，而sdb移动磁盘则出现了"READ CAPACITY failed."(结合之前的日志可能是因为USB外接硬盘未准备好)的失败，若该问题持续可能导致该移动硬盘无法挂载(mount)。
本文转自maclean_007 51CTO博客，原文链接:http://blog.51cto.com/maclean/1278714
