tune2fs: add page (#4297)

pages/linux/tune2fs.md

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+# tune2fs
+
+> Adjust parameters of an ext2, ext3 or ext4 filesystem.
+> May be used on mounted filesystems.
+
+- Set the max number of counts before a filesystem is checked to 2:
+
+`tune2fs -c {{2}} {{/dev/sdXN}}`
+
+- Set the filesystem label to MY_LABEL:
+
+`tune2fs -L {{'MY_LABEL'}} {{/dev/sdXN}}`
+
+- Enable discard and user-specified extended attributes for a filesystem:
+
+`tune2fs -o {{discard,user_xattr}} {{/dev/sdXN}}`
+
+- Enable journaling for a filesystem:
+
+`tune2fs -o^{{nobarrier}} {{/dev/sdXN}}`