ex29
This commit is contained in:
wizardforcel
parent
007b46e54b
commit
7d6262f000
|
|
@ -0,0 +1,116 @@
|
|||
# 练习 29：内核：内核消息，`dmesg`
|
||||
|
||||
> 原文：[Exercise 29. Kernel: kernel messages, dmesg](https://archive.fo/aZwFG)
|
||||
|
||||
> 译者：[飞龙](https://github.com/wizardforcel)
|
||||
|
||||
> 协议：[CC BY-NC-SA 4.0](http://creativecommons.org/licenses/by-nc-sa/4.0/)
|
||||
|
||||
> 自豪地采用[谷歌翻译](https://translate.google.cn/)
|
||||
|
||||
那么，如果你到达了这里，现在是谈谈[内核](http://en.wikipedia.org/wiki/Kernel_%28computing%29)的时候了。我们将使用维基百科的操作系统内核定义，开始这个讨论：
|
||||
|
||||
> 在计算机中，内核（来自德语 Kern）是大多数计算机操作系统的主要组成部分；它是应用程序和硬件级别上进行的实际数据处理之间的桥梁。内核的职责包括管理系统的资源（硬件和软件组件之间的通信）。通常，作为操作系统的基本组件，内核可以为资源（特别是处理器和 I/O 设备）提供最底层的抽象，应用软件必须控制它来执行其功能。它通常通过进程间通信机制和系统调用，使这些设施可用于应用程序进程。
|
||||
|
||||
这是维基百科告诉我们的，Linux 内核的具体内容：
|
||||
|
||||
> Linux 内核是 Linux 系列类 Unix 操作系统使用的操作系统内核。它是自由和开源软件最突出的例子之一。它支持真正的抢占式多任务（在用户模式和内核模式下），虚拟内存，共享库，按需加载，共享的写时复制（COW）可执行文件，内存管理，互联网协议组和线程。
|
||||
|
||||
现在是访问相应的维基百科文章的好时机，并花费一些时间疯狂点击所有可怕的术语，它们描述 Linux 内核的技术特性。这样做之后，让我们谈谈更多的单调的主题，这是内核告诉我们的一种方式。例如，如果 USB 记忆棒连接到计算机，或者网络链接断开或挂载了文件系统，则会发生这种情况。为了能够告诉你所有这些东西，内核使用一种称为显示消息 或驱动消息的机制，其名称缩写为`dmesg`。
|
||||
|
||||
该机制由固定大小的缓冲区表示，内核向它写入消息。在 Debian Linux 上，系统日志守护进程启动后，从缓冲区发布的信息也会被复制到`/var/log/dmesg`。这样做是为了保留这些消息，否则将被新的消息覆盖。
|
||||
|
||||
`dmesg`也是工具的名称，它允许你查看当前在内核缓冲区中的那些消息，并更改此缓冲区大小。
|
||||
|
||||
让我总结一下`dmesg`相关的文件和程序：
|
||||
|
||||
+ `dmesg` - 打印或控制内核环缓冲区
|
||||
+ `/var/log/dmseg` - Debian 发行版中的日志文件，仅包含系统引导期间的`dmesg`消息副本，而不包含时间戳。
|
||||
+ `/var/log/kern.log` - Debian 发行版中的日志文件，包含所有`dmesg`消息的副本，包括时间戳请注意，`rsyslog` 日志守护进程启动后，这个时间戳开始变化，这意味着`rsyslog`启动前，所有引导时的消息将具有相同的时间戳。此文件本身包含`/var/log/dmseg`。
|
||||
+ `/var/log/messages` - Debian 发行版中的日志文件，记录所有非调试和非关键消息。它本身包含`/var/log/dmesg`。
|
||||
+ `/var/log/syslog` - Debian 发行版中的日志文件，记录了所有信息，但权限相关的信息除外。它包含`/var/log/messages`和`/var/log/kern.log`中的所有消息。
|
||||
|
||||
## 这样做
|
||||
|
||||
```
|
||||
1: date
|
||||
2: sudo umount /tmp ; sudo mount /tmp
|
||||
3: sudo tail -f /var/log/dmesg /var/log/messages /var/log/syslog /var/log/kern.log
|
||||
```
|
||||
|
||||
## 你会看到什么
|
||||
|
||||
```
|
||||
user1@vm1:~$ date
|
||||
Tue Jul 24 06:55:33 EDT 2012
|
||||
user1@vm1:~$ sudo umount /tmp ; sudo mount /tmp
|
||||
user1@vm1:~$ dmesg | tail
|
||||
[ 7.166240] tun: Universal TUN/TAP device driver, 1.6
|
||||
[ 7.166242] tun: (C) 1999-2004 Max Krasnyansky <maxk@qualcomm.com>
|
||||
[ 7.432019] ADDRCONF(NETDEV_UP): eth0: link is not ready
|
||||
[ 7.435270] e1000: eth0 NIC Link is Up 1000 Mbps Full Duplex, Flow Control: RX
|
||||
[ 7.435927] ADDRCONF(NETDEV_CHANGE): eth0: link becomes ready
|
||||
[ 17.472049] tap0: no IPv6 routers present
|
||||
[ 17.592044] eth0: no IPv6 routers present
|
||||
[ 217.497357] kjournald starting. Commit interval 5 seconds
|
||||
[ 217.497561] EXT3 FS on sda8, internal journal
|
||||
[ 217.497564] EXT3-fs: mounted filesystem with ordered data mode.
|
||||
user1@vm1:~$ sudo tail /var/log/dmesg /var/log/messages /var/log/syslog /var/log/kern.log
|
||||
==> /var/log/dmesg <==
|
||||
[ 6.762569] EXT3 FS on sda5, internal journal
|
||||
[ 6.762572] EXT3-fs: mounted filesystem with ordered data mode.
|
||||
[ 6.767237] kjournald starting. Commit interval 5 seconds
|
||||
[ 6.767407] EXT3 FS on sda6, internal journal
|
||||
[ 6.767410] EXT3-fs: mounted filesystem with ordered data mode.
|
||||
[ 7.166240] tun: Universal TUN/TAP device driver, 1.6
|
||||
[ 7.166242] tun: (C) 1999-2004 Max Krasnyansky <maxk@qualcomm.com>
|
||||
[ 7.432019] ADDRCONF(NETDEV_UP): eth0: link is not ready
|
||||
[ 7.435270] e1000: eth0 NIC Link is Up 1000 Mbps Full Duplex, Flow Control: RX
|
||||
[ 7.435927] ADDRCONF(NETDEV_CHANGE): eth0: link becomes ready
|
||||
|
||||
==> /var/log/messages <==
|
||||
Jul 24 06:52:07 vm1 kernel: [ 6.767407] EXT3 FS on sda6, internal journal
|
||||
Jul 24 06:52:07 vm1 kernel: [ 6.767410] EXT3-fs: mounted filesystem with ordered data mode.
|
||||
Jul 24 06:52:07 vm1 kernel: [ 7.166240] tun: Universal TUN/TAP device driver, 1.6
|
||||
Jul 24 06:52:07 vm1 kernel: [ 7.166242] tun: (C) 1999-2004 Max Krasnyansky <maxk@qualcomm.com>
|
||||
Jul 24 06:52:07 vm1 kernel: [ 7.432019] ADDRCONF(NETDEV_UP): eth0: link is not ready
|
||||
Jul 24 06:52:07 vm1 kernel: [ 7.435270] e1000: eth0 NIC Link is Up 1000 Mbps Full Duplex, Flow Control: RX
|
||||
Jul 24 06:52:07 vm1 kernel: [ 7.435927] ADDRCONF(NETDEV_CHANGE): eth0: link becomes ready
|
||||
Jul 24 06:55:36 vm1 kernel: [ 217.497357] kjournald starting. Commit interval 5 seconds
|
||||
Jul 24 06:55:36 vm1 kernel: [ 217.497561] EXT3 FS on sda8, internal journal
|
||||
Jul 24 06:55:36 vm1 kernel: [ 217.497564] EXT3-fs: mounted filesystem with ordered data mode.
|
||||
|
||||
==> /var/log/syslog <==
|
||||
Jul 24 06:52:08 vm1 acpid: 1 rule loaded
|
||||
Jul 24 06:52:08 vm1 acpid: waiting for events: event logging is off
|
||||
Jul 24 06:52:08 vm1 /usr/sbin/cron[882]: (CRON) INFO (pidfile fd = 3)
|
||||
Jul 24 06:52:08 vm1 /usr/sbin/cron[883]: (CRON) STARTUP (fork ok)
|
||||
Jul 24 06:52:08 vm1 /usr/sbin/cron[883]: (CRON) INFO (Running @reboot jobs)
|
||||
Jul 24 06:52:16 vm1 kernel: [ 17.472049] tap0: no IPv6 routers present
|
||||
Jul 24 06:52:16 vm1 kernel: [ 17.592044] eth0: no IPv6 routers present
|
||||
Jul 24 06:55:36 vm1 kernel: [ 217.497357] kjournald starting. Commit interval 5 seconds
|
||||
Jul 24 06:55:36 vm1 kernel: [ 217.497561] EXT3 FS on sda8, internal journal
|
||||
Jul 24 06:55:36 vm1 kernel: [ 217.497564] EXT3-fs: mounted filesystem with ordered data mode.
|
||||
|
||||
==> /var/log/kern.log <==
|
||||
Jul 24 06:52:07 vm1 kernel: [ 7.166240] tun: Universal TUN/TAP device driver, 1.6
|
||||
Jul 24 06:52:07 vm1 kernel: [ 7.166242] tun: (C) 1999-2004 Max Krasnyansky <maxk@qualcomm.com>
|
||||
Jul 24 06:52:07 vm1 kernel: [ 7.432019] ADDRCONF(NETDEV_UP): eth0: link is not ready
|
||||
Jul 24 06:52:07 vm1 kernel: [ 7.435270] e1000: eth0 NIC Link is Up 1000 Mbps Full Duplex, Flow Control: RX
|
||||
Jul 24 06:52:07 vm1 kernel: [ 7.435927] ADDRCONF(NETDEV_CHANGE): eth0: link becomes ready
|
||||
Jul 24 06:52:16 vm1 kernel: [ 17.472049] tap0: no IPv6 routers present
|
||||
Jul 24 06:52:16 vm1 kernel: [ 17.592044] eth0: no IPv6 routers present
|
||||
Jul 24 06:55:36 vm1 kernel: [ 217.497357] kjournald starting. Commit interval 5 seconds
|
||||
Jul 24 06:55:36 vm1 kernel: [ 217.497561] EXT3 FS on sda8, internal journal
|
||||
Jul 24 06:55:36 vm1 kernel: [ 217.497564] EXT3-fs: mounted filesystem with ordered data mode.
|
||||
```
|
||||
|
||||
## 解释
|
||||
|
||||
1. 打印出当前日期和时间。
|
||||
1. 从内核消息缓冲区打印最后 10 条消息。
|
||||
1. 从`/var/log/dmesg`, `/var/log/messages`, `/var/log/syslog`和`/var/log/kern.log`打印最后 10 条消息。
|
||||
|
||||
## 附加题
|
||||
|
||||
这就完了，没有附加题，哇哦！
|
||||
Loading…
Reference in New Issue