chore: reserved blocks in linux

knowledge base/set reserved blocks on filesystems.md

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+# Set reserved blocks on filesystems
+
+```sh
+# EXT
+tune2fs -m 1 /dev/sdXY
+tune2fs -r numOfBlocks device
+
+# XFS
+xfs_io -x -c 'resblks' '/path/to/fs'
+```
+
+## Sources
+
+- [Reserved space for root on a filesystem - why?]
+- [How to determine the reserved blocks in XFS filesystem?]
+
+<!--
+  Reference
+  ═╬═Time══
+  -->
+
+[how to determine the reserved blocks in xfs filesystem?]: https://lore.kernel.org/all/CAJtCNH2irjpu3T57XPHPXHZ0FXm7V-diaA4g3DtjAmcRV2xmWA@mail.gmail.com/T/
+[reserved space for root on a filesystem - why?]: https://unix.stackexchange.com/questions/7950/reserved-space-for-root-on-a-filesystem-why

snippets/filesystems.sh

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+#/usr/bin/env sh
+
+# Get the *sector* size of partitions in 512-byte sectors
+sudo blockdev --getsz '/dev/nvme0n1p1'
+
+# Get the *block* size of partitions
+sudo blockdev --getbsz '/dev/nvme0n1p1'