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---
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layout: doc
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title: DiskTRIM
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permalink: /doc/DiskTRIM/
redirect_from: /wiki/DiskTRIM/
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---
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VMs have already TRIM enabled by default, but dom0 doesn't. There are some security implications (read for example [this article ](http://asalor.blogspot.com/2011/08/trim-dm-crypt-problems.html )), but IMO not very serious.
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To enable TRIM in dom0 you need:
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1. Get your LUKS device UUID:
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```
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ls /dev/mapper/luks-*
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```
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2. Add entry to `/etc/crypttab` (replace luks-\<UUID\> with the device name and the \<UUID\> with UUID alone):
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```
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luks-< UUID > UUID=< UUID > none allow-discards
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```
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3. Add `rd.luks.allow-discards=1` to kernel cmdline (`/etc/default/grub`, GRUB\_CMDLINE\_LINUX line)
4. Rebuild grub config (`grub2-mkconfig -o /boot/grub2/grub.cfg`)
5. Rebuild initrd **in hostonly mode** :
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```
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dracut -H -f
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```
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6. Add "discard" option to `/etc/fstab` for root device
7. Reboot the system, verify that allow-discards is really enabled (`dmsetup table`)
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There is a [bug affecting allow-discards option ](https://bugzilla.redhat.com/show_bug.cgi?id=890533 ), once it will be fixed, first two steps will be no longer needed.
