Update cheatsheets

ulimit

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+---
+syntax: markdown
+tags: [tldr, common]
+source: https://github.com/tldr-pages/tldr.git
+---
+# ulimit
+
+> Get and set user limits.
+> More information: <https://manned.org/ulimit>.
+
+- Get the properties of all the user limits:
+
+`ulimit -a`
+
+- Get hard limit for the number of simultaneously opened files:
+
+`ulimit -H -n`
+
+- Get soft limit for the number of simultaneously opened files:
+
+`ulimit -S -n`
+
+- Set max per-user process limit:
+
+`ulimit -u 30`