Linux EFAULT (errno 14) — Bad Address (Memory Access Error)

Linux EFAULT error occurs when a system call is given a pointer to invalid memory, indicating a programming bug or memory corruption in the application. This guide covers everything you need to know about this topic, including common causes, step-by-step solutions, and answers to frequently asked questions.

Here are the key things to understand: EFAULT (errno 14) means a system call was passed a pointer outside the process's accessible address space. This is almost always a programming bug — passing NULL, freed, or uninitialized pointers to syscalls. The kernel validates user-space pointers before accessing them and returns EFAULT if invalid. Unlike SIGSEGV which crashes the process, EFAULT is returned as an error code allowing recovery. Common in C programs with incorrect memory management. Understanding these fundamentals will help you diagnose and resolve this issue more effectively.

The most common reasons this occurs include: Passing NULL pointer to a system call that expects valid memory. Using a pointer to freed memory (use-after-free). Buffer allocated on the stack that has gone out of scope. Incorrect pointer arithmetic pointing outside allocated buffer. Memory corruption from buffer overflow in a different part of the program. Identifying the root cause is the first step toward finding the right solution.

To resolve this, follow these recommended steps: Run the program under Valgrind: valgrind --track-origins=yes ./program to detect memory errors. Compile with AddressSanitizer: gcc -fsanitize=address -g program.c. Use strace to identify which system call returns EFAULT: strace -e trace=all ./program. Enable core dumps: ulimit -c unlimited, then analyze with gdb ./program core. Review code for NULL pointer checks before system calls. If these steps do not resolve the issue, consider consulting additional resources or a qualified professional.

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