EMFILE

EMFILE is an errno value used on POSIX-compatible systems to signal that a process has reached the limit for the number of open file descriptors. When a process attempts to open a file, create a socket, or otherwise obtain a new descriptor beyond its allowed limit, a system call may fail with EMFILE.

EMFILE refers to the per-process limit on open file descriptors. It is distinct from ENFILE, which indicates that the entire system has run out of file descriptors. A process can encounter EMFILE even if the system as a whole has free descriptors if the per-process table is exhausted or if descriptors are not released promptly.

Common causes include long-running servers with many active connections, resource leaks where descriptors are never closed, or excessive parallelism that exceeds the per-process limit. It can also occur after forking many child processes without proper descriptor management.

Diagnosis and remediation typically involve checking and adjusting limits. The soft and hard limits for the number of open files can be viewed and modified using tools like getrlimit in code or the shell command ulimit -n; current limits are also visible in /proc/self/limits on Linux. If appropriate, increase the soft limit, and, if feasible, raise the hard limit or system-wide limits such as fs.file-max. In application code, ensure timely closure of files and sockets, close descriptors in finally blocks, and consider resource pooling or limiting concurrent operations to stay within allowed limits. Understanding the distinction between EMFILE and ENFILE helps target whether the issue is per-process or system-wide.