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Systems & Data Center · Intermediate

ulimit

A shell built-in that views or sets per-process resource limits such as open files and processes.

Definition

Soft limits can be raised by users up to hard limits, which only root can increase. Persistent limits are set in /etc/security/limits.conf or limits.d, or LimitNOFILE= in systemd units.

Example

ulimit -n 65535 raises the open-file limit for the current shell.

Exam tip

For systemd services, limits.conf does not apply; set LimitNOFILE in the unit file.

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