Skip to main content

[转]什么是SysRq"魔术组合键"?

很有意思, 等我有空试一试

//原文

根据Linux内核文档介绍:

这是一组'魔术组合键'，只要内核没有被完全锁住，不管内核在做什么事情，使用这些组合键可以立即打印出内核的信息。

使用sysrq组合键是了解系统目前运行情况的最好方式。如果系统出现挂起的情况或者在诊断一些和内核相关，比较怪异，比较难重现的问题的时候，使用sysrq键是一个比较好的方式。

如何打开和关闭SysRq组合键?

为了安全起见，在红帽企业版Linux里面，默认SysRq组合键是关闭的。 打开这个功能，运行:


# echo 1 > /proc/sys/kernel/sysrq

关闭这个功能:


# echo 0 > /proc/sys/kernel/sysrq


如果想让此功能一直生效，在/etc/sysctl.conf里面设置kernel.sysrq的值为1. 重新启动以后，此功能将会自动打开。

kernel.sysrq = 1

因为打开sysrq键的功能以后，有终端访问权限的用户将会拥有一些特殊的功能。因此，除非是要调试，解决问题，一般情况下，不要打开此功能。如果一定要打开，请确保您的终端访问的安全性。

如何触发一个sysrq事件?

有几种方式可以触发sysrq事件。在带有AT键盘的一般系统上，在终端上输入一下组合键:

Alt+PrintScreen+[CommandKey]

例 如，要让内核导出内存信息(CommandKey "m")，您应该同时按下Alt 和 Print Screen 键，然后按下 m 键. 提示: 此组合键在Xwindows上是无法使用的。所以，您先要切换到文本虚拟终端下。如果您现在是在图形界面，可以按Ctrl+Alt+F1切换到虚拟终端。

在串口终端上,要想获得同样的效果，需要先在终端上发送Break信号，然后在5秒内输入sysrq组合键。

如果您在机器上有root权限，您可以把commandkey字符写入到/proc/sysrq-trigger文件。这可以帮助您通过脚本或者您不在系统终端上的时候触发sysrq事件。


# echo 'm' > /proc/sysrq-trigger


当我触发一个sysrq事件的时候，接过保存在什么地方?

当一个sysrq命令被触发，内核将会打印信息到内核的环形缓冲并输出到系统控制台。此信息一般也会通过syslog输出到/var/log/messages.

有时候，可能系统已经无法响应，syslogd可能无法记录此信息。在这种情况下，建议您配置一个串口终端来收集这个信息。

那些类型的sysrq事件可以被触发?

sysrq功能被打开后，有几种sysrq事件可以被触发。不同的内核版本可能会有些不同。但有一些是共用的:

* m - 导出关于内存分配的信息

* t - 导出线程状态信息

* p - 到处当前CPU寄存器信息和标志位的信息

* c - 故意让系统崩溃(在使用netdump或者diskdump的时候有用)


* s - 立即同步所有挂载的文件系统

* u - 立即重新挂载所有的文件系统为只读

* b - 立即重新启动系统

* o - 立即关机(如果机器配置并支持此项功能)
Labels:

Comments

Post a Comment

Popular posts from this blog

Determine Perspective Lines With Off-page Vanishing Point

In perspective drawing, a vanishing point represents a group of parallel lines, in other words, a direction. For any point on the paper, if we want a line towards the same direction (in the 3d space), we simply draw a line through it and the vanishing point. But sometimes the vanishing point is too far away, such that it is outside the paper/canvas. In this example, we have a point P and two perspective lines L1 and L2. The vanishing point VP is naturally the intersection of L1 and L2. The task is to draw a line through P and VP, without having VP on the paper. I am aware of a few traditional solutions: 1. Use extra pieces of paper such that we can extend L1 and L2 until we see VP. 2. Draw everything in a smaller scale, such that we can see both P and VP on the paper. Draw the line and scale everything back. 3. Draw a perspective grid using the Brewer Method. #1 and #2 might be quite practical. #3 may not guarantee a solution, unless we can measure distances/p...
3 comments
Read More »

Hardware Password Manager

[Updates 2025-01-20] The original blog post assumes that all passwords are stored in one password manager, and the password manager either unlocks everything or nothing (e.g. Keepass). After discussing with friends, I realized that if I use something like pass , and I use a hardware GPG token, I can actually store and sync all encrypted passwords to all devices, because I will only decrypt the passwords on demand, and the computer will not see the GPG private key. The compromise is that the computer will see the list of all password entries (e.g. accounts), as well as a few other issues . I've been using Keepass for many years. I don't use online password services because I cannot fully trust them. Besides, I may not always have Internet connection, which is why I also don't use a self-hosted service. Everything has been working fine, until I turn my paranoid knob to the max. Here's the thought experiment . The Imaginary Scenario Let's say I have 100 PCs for differe...
Post a Comment
Read More »

ESP32S3: Flash Encryption and Secure Boot

Flash encryption and secure boot are useful security features for ESP32S3 chip. While not perfect, they definitely make it harder to extract the secrets in the chip. However, it is tricky to enable both features at the same time. The topic is actually discussed in the official documentation: ESP32S3 Security Features Security Features Enablement Workflows Especially, the second one mentioned it is recommended to enable flash encryption before secure boot. But I still find the documentation confusing. In the end I was able to successfully enable both, here's my findings. My Understanding After my adventure, here's what I think could have worked. WARNING, this is untested. Follow  Security Features Enablement Workflows : Burn all the keys, as long as their purpose eFuses and read/write protections Burn other security eFuses, but DO NOT burn ENABLE_SECURITY_DOWNLOAD in the middle, which is mentined at the end of the instruction for both flash encryption and secure boot. Burn...
Post a Comment
Read More »