A Linux server repeatedly reports “fork: cannot allocate memory” not because RAM is exhausted but due to excessive Java threads causing PID allocation failures, and the kernel mistakenly maps those failures to the ENOMEM error code.
This article analyzes why Linux reports "fork: cannot allocate memory" when the real issue is an excessive number of threads or PID allocation failures, explains the kernel's do_fork and alloc_pid implementations, and offers guidance for diagnosing and fixing such misleading ENOMEM errors.
The article explains why Linux’s fork() can return a misleading “fork: cannot allocate memory” error, tracing the issue to PID allocation failures in the kernel’s do_fork and alloc_pid functions, and shows how excessive threads, not actual memory shortage, trigger the problem.
The article explains why Linux reports "fork: cannot allocate memory" when the real issue is PID allocation failure caused by excessive threads, analyzes the kernel's do_fork and alloc_pid implementations, and shows that newer kernels still return ENOMEM for non‑memory errors.
