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139 lines
5.6 KiB
Markdown
139 lines
5.6 KiB
Markdown
# Auto-mounting other encrypted partitions
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If you've set up multiple encrypted partitions (a common reason to do so is
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having multiple drives), you will likely want to have these other partitions
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mounted automatically after the root partition, during the boot process.
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> [!TIP]
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> You can safely skip this guide if you only have a single encrypted partition
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> (with the root).
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## /etc/crypttab
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Obviously, with encrypted partitions, you can't simply specify the mounting
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instructions into your `/etc/fstab`, instead, there is a special file designed
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precisely for this purpose: `/etc/crypttab`. Just like with `fstab`, systemd
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will read `crypttab` during boot and attempt to mount the entries inside of it.
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From here, you can add entries for mounting your encrypted partitions, like so:
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```txt
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# Configuration for encrypted block devices.
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# See crypttab(5) for details.
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# NOTE: Do not list your root (/) partition here, it must be set up
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# beforehand by the initramfs (/etc/mkinitcpio.conf).
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# <name> <device> <password> <options>
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cryptdata LABEL=DATA none discard
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```
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> [!NOTE]
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> The `discard` option is specified to enable TRIM on SSDs, which should improve
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> their lifespan. It is not necessary if you're using an HDD.
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The `<name>` option specifies the name of the decrypted mapper device, so in
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this case, the decrypted device would be in `/dev/mapper/cryptdata`. We can then
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add mounting instructions into `/etc/fstab`, that work with this mapper device.
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Specifying a partition in here will result in you being prompted for a
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decryption password each time during boot. If you only have one encrypted
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partition like this, and your root partition isn't encrypted, this will be
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sufficient for you.
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## Key files
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That said, if you have multiple encrypted partitions, or your root partition is
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encrypted too, you might find it pretty annoying to have to enter a password for
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each of your encrypted partitions every time.
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For this reason, crypttab includes the `<password>` option, which we originally
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left as `none`. We can use this field to specify a path to a "key file". This is
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basically just a file that holds the encryption password.
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> [!IMPORTANT]
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> Storing the decryption password in a key file like this can only be done
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> safely if that key file is stored on another encrypted partition, which we
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> decrypted in another way (usually by being prompted for the password).
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>
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> In this example, we'll be storing the key files in `/etc/secrets`, which is
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> safe as our root partition is encrypted.
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LUKS encryption has support for having multiple keys for the same parition.
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We'll utilize this support and add 2nd key slot to all of the partitions that we
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wish to auto-mount.
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```bash
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mkdir -p /etc/secrets
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dd if=/dev/random bs=4096 count=1 of=/etc/secrets/keyFile-data.bin
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chmod -R 400 /etc/secrets
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chmod 700 /etc/secrets
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```
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The bs argument signifies a block size (in bits), so this will create 4096-bit keys.
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Now we can add this key into our LUKS encrypted data partition:
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```bash
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cryptsetup luksAddKey /dev/disk/by-label/DATA --new-keyfile /etc/secrets/keyFile-data.bin
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```
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Finally, we'll modify the `/etc/crypttab` record and add our new keyfile as the
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password for this partition:
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```txt
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# Configuration for encrypted block devices.
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# See crypttab(5) for details.
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# NOTE: Do not list your root (/) partition here, it must be set up
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# beforehand by the initramfs (/etc/mkinitcpio.conf).
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# <name> <device> <password> <options>
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cryptdata LABEL=DATA /etc/secrets/keyFile-data.bin discard
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```
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### /etc/fstab
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While the crypttab file opens the encrypted block devices and creates the mapper
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interfaces for them, to mount those to a concrete directory, we still use
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/etc/fstab. Below is the /etc/fstab that I use on my system:
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<!-- markdownlint-disable MD010 MD013 -->
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```text
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# Static information about the filesystems.
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# See fstab(5) for details.
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# <file system> <dir> <type> <options> <dump> <pass>
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# region: Physical partitions
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# /dev/nvme0n1p2 LABEL=SWAP UUID=d262a2e5-a1a3-42b1-ac83-18639f5e8f3d
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/dev/disk/by-label/SWAP none swap defaults 0 0
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# /dev/nvme0n1p1 LABEL=EFI UUID=44E8-EB26
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/dev/disk/by-label/EFI /efi vfat rw,relatime,fmask=0137,dmask=0027,codepage=437,iocharset=ascii,shortname=mixed,utf8,errors=remount-ro 0 2
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# endregion
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# region: BTRFS subvolumes on /dev/disk/by-label/ARCH (decrypted from ARCH_LUKS)
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# /dev/mapper/cryptfs LABEL=ARCH UUID=bffc7a62-0c7e-4aa9-b10e-fd68bac477e0
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/dev/mapper/cryptfs / btrfs rw,noatime,compress=zstd:1,ssd,space_cache=v2,subvol=/@ 0 1
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/dev/mapper/cryptfs /home btrfs rw,noatime,compress=zstd:1,ssd,space_cache=v2,subvol=/@home 0 1
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/dev/mapper/cryptfs /var/log btrfs rw,noatime,compress=zstd:2,ssd,space_cache=v2,subvol=/@log 0 1
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/dev/mapper/cryptfs /var/cache btrfs rw,noatime,compress=zstd:3,ssd,space_cache=v2,subvol=/@cache 0 1
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/dev/mapper/cryptfs /tmp btrfs rw,noatime,compress=no,ssd,space_cache=v2,subvol=/@tmp 0 1
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/dev/mapper/cryptfs /data btrfs rw,noatime,compress=zstd:5,ssd,space_cache=v2,subvol=/@data 0 2
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/dev/mapper/cryptfs /.btrfs btrfs rw,noatime,ssd,space_cache=v2 0 2 # btrfs root
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# endregion
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# region: Bind mounts
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# Write kernel images to /efi/arch, not directly to efi system partition (esp), to avoid conflicts when dual booting
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/efi/arch-1 /boot none rw,fmask=0022,dmask=0022,codepage=437,iocharset=ascii,shortname=mixed,utf8,errors=remount-ro,bind 0 0
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# endregion
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```
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<!-- markdownlint-enable MD010 MD013 -->
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