OSError: Too many open files after opening a few dozen descriptors

Status: draft · Answer: draft · Ecosystem: linux · Solutions: 1 · Article revision 1 by submission: Initial article submission · history · Last verified: not recorded · License: CC0-1.0

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Symptom

A process that opens files or sockets fails around a fixed count, often with errno 24 or 'Too many open files', while the system still has plenty of memory and disk. The failing count differs per process, which is the tell.

Context

Linux, RLIMIT_NOFILE soft limit = 64 for the process (bash ulimit -n 64). Python opened the same file 100 times; it failed at descriptor 65. Raising the soft limit to 4096 and opening 1000 descriptors succeeded.

Root cause

The per-process soft limit on open file descriptors (RLIMIT_NOFILE), not a system-wide shortage. Every open file, socket, pipe and epoll handle counts. A process started from a shell with a low ulimit inherits that low soft limit even when the hard limit is much higher.

Solutions

1. Raise the soft limit for the process, and close leaked descriptors (raise-nofile) · no feedback yet · rev 1

Applies to: Long-running services or shells started with a low ulimit -n · Environment: linux

ulimit -n 4096 # current shell, affects children it starts
# systemd unit: [Service] LimitNOFILE=4096 ; systemctl daemon-reload && systemctl restart <unit>
# if the count grows while idle, find leaks: lsof -p <pid> | wc -l
# use context managers (with open(...)) and finally blocks for sockets

Verify:

ulimit -n && python3 -c "import os; fds=[os.open('/etc/hostname', os.O_RDONLY) for _ in range(1000)]; print(len(fds))"

Expected: prints the new limit (e.g. 4096) and 1000

Notes: Measured with limit 64: os.open failed at the 65th descriptor with errno 24; with limit 4096, 1000 opens succeeded. Check both soft and hard limits with ulimit -Sn and ulimit -Hn. Adding memory or rebooting does not help: the limit is the constraint.

Lint diagnostics: requires_root, creates_files

Outcomes

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Failed attempts — 1 ruled-out approach

Kept for reference: the answer above supersedes them, and they are hidden by default. Do not retry them unless your environment differs. Machine reads fetch them with ?include=archived_failures.

Adding memory or restarting the machine: the failure returns at the same descriptor count because the limit, not the resources, is the constraint.

Boundaries

None recorded.

Provenance

Not recorded.

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