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0

So I was reading How Linux Works by Brian Ward. In it, he says, the user-space applications going bad will not wreck the system.

Figure 1-1. General Linux system organization
There is a critical difference between the ways that the kernel and user processes run: The kernel runs in kernel
mode, and the user processes run in user mode. Code running in kernel mode has unrestricted access to the
processor and main memory. This is a powerful but dangerous privilege that allows a kernel process to easily
crash the entire system. The area that only the kernel can access is called kernel space.

User mode, in comparison, restricts access to a (usually quite small)
subset of memory and safe CPU operations. User space refers to the
parts of main memory that the user processes can access. If a process
makes a mistake and crashes, the consequences are limited and can be
cleaned up by the kernel. This means that if your web browser crashes,
it probably won’t take down the scientific computation that you’ve
been running in the background for days.

In theory, a user process gone haywire can’t cause serious damage to
the rest of the system. In reality, it depends on what you consider
“serious damage,” as well as the particular privileges of the process,
because some processes are allowed to do more than others. For
example, can a user process completely wreck the data on a disk? With
the correct permissions, yes—and you may consider this to be fairly
dangerous. There are safeguards to prevent this, however, and most
processes simply aren’t allowed to wreak havoc in this manner.

I have read that a web server, for example, runs in user-space and I have seen it consuming all the memory of the system and forcing the server to be crashed. But what the author says is contradicting to this.

I don't know if I am misinterpreting what the author is trying to say. My apologies.

Can someone please explain if the userspace applications can wreck the system or not and why.

Thanks for your humble help.

linux linux-kernel memory

share|improve this question

asked 15 mins ago

Vignesh SPVignesh SP

51

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  "consuming all the memory of the system and forcing the server to be crashed" ... The system must have been swapping heavily, giving the impression of non-responsiveness. Otherwise the OOM killer would have come out of retirement and taken care of the web server.
  
  – muru
  11 mins ago
  

  
  
  
  

add a comment | 

0

So I was reading How Linux Works by Brian Ward. In it, he says, the user-space applications going bad will not wreck the system.

Figure 1-1. General Linux system organization
There is a critical difference between the ways that the kernel and user processes run: The kernel runs in kernel
mode, and the user processes run in user mode. Code running in kernel mode has unrestricted access to the
processor and main memory. This is a powerful but dangerous privilege that allows a kernel process to easily
crash the entire system. The area that only the kernel can access is called kernel space.

User mode, in comparison, restricts access to a (usually quite small)
subset of memory and safe CPU operations. User space refers to the
parts of main memory that the user processes can access. If a process
makes a mistake and crashes, the consequences are limited and can be
cleaned up by the kernel. This means that if your web browser crashes,
it probably won’t take down the scientific computation that you’ve
been running in the background for days.

In theory, a user process gone haywire can’t cause serious damage to
the rest of the system. In reality, it depends on what you consider
“serious damage,” as well as the particular privileges of the process,
because some processes are allowed to do more than others. For
example, can a user process completely wreck the data on a disk? With
the correct permissions, yes—and you may consider this to be fairly
dangerous. There are safeguards to prevent this, however, and most
processes simply aren’t allowed to wreak havoc in this manner.

I have read that a web server, for example, runs in user-space and I have seen it consuming all the memory of the system and forcing the server to be crashed. But what the author says is contradicting to this.

I don't know if I am misinterpreting what the author is trying to say. My apologies.

Can someone please explain if the userspace applications can wreck the system or not and why.

Thanks for your humble help.

linux linux-kernel memory

share|improve this question

asked 15 mins ago

Vignesh SPVignesh SP

51

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  "consuming all the memory of the system and forcing the server to be crashed" ... The system must have been swapping heavily, giving the impression of non-responsiveness. Otherwise the OOM killer would have come out of retirement and taken care of the web server.
  
  – muru
  11 mins ago
  

  
  
  
  

add a comment | 

So I was reading How Linux Works by Brian Ward. In it, he says, the user-space applications going bad will not wreck the system.

Figure 1-1. General Linux system organization
There is a critical difference between the ways that the kernel and user processes run: The kernel runs in kernel
mode, and the user processes run in user mode. Code running in kernel mode has unrestricted access to the
processor and main memory. This is a powerful but dangerous privilege that allows a kernel process to easily
crash the entire system. The area that only the kernel can access is called kernel space.

User mode, in comparison, restricts access to a (usually quite small)
subset of memory and safe CPU operations. User space refers to the
parts of main memory that the user processes can access. If a process
makes a mistake and crashes, the consequences are limited and can be
cleaned up by the kernel. This means that if your web browser crashes,
it probably won’t take down the scientific computation that you’ve
been running in the background for days.

In theory, a user process gone haywire can’t cause serious damage to
the rest of the system. In reality, it depends on what you consider
“serious damage,” as well as the particular privileges of the process,
because some processes are allowed to do more than others. For
example, can a user process completely wreck the data on a disk? With
the correct permissions, yes—and you may consider this to be fairly
dangerous. There are safeguards to prevent this, however, and most
processes simply aren’t allowed to wreak havoc in this manner.

I have read that a web server, for example, runs in user-space and I have seen it consuming all the memory of the system and forcing the server to be crashed. But what the author says is contradicting to this.

I don't know if I am misinterpreting what the author is trying to say. My apologies.

Can someone please explain if the userspace applications can wreck the system or not and why.

Thanks for your humble help.

linux linux-kernel memory

share|improve this question

asked 15 mins ago

Vignesh SPVignesh SP

51

share|improve this question

asked 15 mins ago

Vignesh SPVignesh SP

51

share|improve this question

asked 15 mins ago

Vignesh SPVignesh SP

51

asked 15 mins ago

Vignesh SPVignesh SP

51

asked 15 mins ago

Vignesh SPVignesh SP

51