What Is a Segmentation Fault in Linux?

To understand the concept of a segmentation fault in a Linux operating system environment, we have to first address the concept of segmentation. In operating systems; under process management, each process is associated with a distinct virtual address space, hence the concept of segmentation.

Supposing a memory location like 0x877 is evident on your Linux operating system. Also, suppose two processes (A and B) have access to read this memory location (0x877).

Process A reading memory location 0x877 will access targeted information at a different RAM location in comparison to Process B because Process B’s attempt to read memory location 0x877 (for targeted info) will also be at a unique RAM location.

Therefore, the issue of segmentation fault arises when a program’s access or access attempt to a memory location is either not allowed or not assigned by the Linux operating system.

This article guide seeks to break down the issue of a segmentation fault in a Linux operating system environment.

Understanding Segmentation Fault

As already discussed, when a process’s attempt to access a memory location is out of protocol (e.g overwriting a systemfile or a write attempt to a read-only file) then a segmentation fault occurs.

Since Linux is part of the Unix family of operating systems, when segfault occurs, SIGSEGV (signal #11) is defined in a signal.h (system header file) is called and sent to the process associated with the segmentation fault.

This signal’s default action is to initiate an abnormal termination which then ends the running process. In the case of this process ending its run, a write operation may take place on the primary application’s core file (completely dependent on the current system configuration). Linux architectures like x86_64, the generation of a segfault leads to the kernel ring buffer receiving a log message from the system kernel.

What Causes Segmentation Faults?

Three main circumstances can be associated with the occurrence of segmentation fault.

  • Software Defect or a Bug – Sometimes a command or a running program encounters a bug or a software defect. A perfect example is during buffer overflow where an end-of-array memory access attempt takes place. A typical solution to such a problem is implementing vendor software updates.
  • Hardware Problem – When the machine you are using to run your Linux operating system distribution has hardware issues (incompetent hardware), its effect will be felt by the virtual memory subsystem. Such hardware incompetency can be associated with defective CPU cache or RAM DIMM.
  • Executing an Incomplete Program – When a program is not built/compiled correctly and its execution initiated, the occurrence of a segmentation fault becomes inevitable.

The Implication of a Segmentation Fault

We should never interpret a segfault as a kernel error but as a particular process/program error. The system kernel’s role in dealing with segmentation faults is to detect the associated programs’ errors.

In some Linux architectures, the system kernel is privileged enough to print more segfault-related info like PID and process name. If the segmentation fault is linked to multiple unrelated processes, then the virtual memory subsystem is affected by a hardware issue.

A segmentation fault can be programmatically fixed by checking array boundaries, indirect memory allocation (e.g via smart pointers), and shying away from the use of direct pointer arithmetic (an approach reserved for experienced system programmers).

We are now familiar with the concept of a segmentation fault in a Linux operating system environment.

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