In my last article I had shared the steps to encrypt a partition using LUKS. Now in this article I will continue with LUKS disk encryption and will share the steps to auto mount LUKS device with and without encrypt key during boot up of the Linux node. If you have not enabled auto mount using secret key then you can use LUKS passphrase to manually mount the encrypted partition.
Below are some more articles on LUKS based Disk Encryption
- How to Encrypt Hard Disk (partition) using LUKS in Linux
- How to auto mount LUKS encrypted partition using fstab at boot in Linux
- How to encrypt root partition and entire file system using LUKS in Linux
- How to resize LUKS partition (shrink or extend encrypted luks volume) in Linux
- Configure LUKS Network Bound Disk Encryption with clevis & tang server to boot without password
How LUKS Disk Encryption Works?
- The entire block device can be encrypted using LUKS; it's well suited for protecting the data on removable storage media or the laptop disk drives
- LUKS Disk Encryption uses the existing device mapper kernel subsystem
- It also provides passphrase strengthening, which helps protect against dictionary attacks
Auto mount encrypted partition using fstab without key (prompts for LUKS passphrase)
From our last article we already have an LUKS encrypted partition /dev/sdb1, Now you can manually mount the encrypted partition every time node bootsor you can use fstab to auto mount LUKS device during boot stage using LUKS passphrase.
Add below entry to your /etc/fstab
/dev/mapper/secret /secret ext4 defaults 0 0
Next add below entry to /etc/crypttab. Here we are providing the LUKS device name, the mapped partition and the key file location. But since at this stage we have not created any key file, we will put it as none.
secret /dev/sdb1 none
Next reboot the node and check if the reboot halts waiting for LUKS passphrase to mount the encrypted device
Mount LUKS device using fstab with key (No prompt for LUKS passphrase)
LUKS Disk Encryption can use up to 8 key slots to store passwords. We can use these keys to auto mount LUKS device.
Use the below command to check the currently utilised key slots. Here as you see only one key slot is in use where we have set the LUKS passphrase of the encrypted partition.
[root@node1 ~]# cryptsetup luksDump /dev/sdb1
LUKS header information for /dev/sdb1
Version: 1
Cipher name: aes
Cipher mode: xts-plain64
Hash spec: sha256
Payload offset: 4096
MK bits: 256
MK digest: 4f 28 47 d0 91 cd 30 1f c0 78 73 b9 0e 83 cd d6 77 99 bf c8
MK salt: dc 91 2a 87 49 44 a9 2a 75 f7 f4 18 ee 39 54 e2
2f 72 e0 21 ba 07 59 84 75 58 c6 a9 ad 7e 43 ae
MK iterations: 19006
UUID: 1da14492-aec4-4924-905d-e5aa28cbcff4
Key Slot 0: ENABLED
Iterations: 296206
Salt: 06 af 5b fc 27 a3 3c 84 02 d8 1e 89 ec fc c9 15
d8 c4 5e 3c 58 9b 92 0a e3 e5 48 5d 6b da cf 65
Key material offset: 8
AF stripes: 4000
Key Slot 1: DISABLED
Key Slot 2: DISABLED
Key Slot 3: DISABLED
Key Slot 4: DISABLED
Key Slot 5: DISABLED
Key Slot 6: DISABLED
Key Slot 7: DISABLED
To add a new encrypt key to auto mount LUKS device use the below command.
[root@node1 ~]# cryptsetup luksAddKey /dev/sdb1 Enter any existing passphrase: Enter new passphrase for key slot: Verify passphrase:
Next verify the key slots again
[root@node1 ~]# cryptsetup luksDump /dev/sdb1
LUKS header information for /dev/sdb1
Version: 1
Cipher name: aes
Cipher mode: xts-plain64
Hash spec: sha256
Payload offset: 4096
MK bits: 256
MK digest: 4f 28 47 d0 91 cd 30 1f c0 78 73 b9 0e 83 cd d6 77 99 bf c8
MK salt: dc 91 2a 87 49 44 a9 2a 75 f7 f4 18 ee 39 54 e2
2f 72 e0 21 ba 07 59 84 75 58 c6 a9 ad 7e 43 ae
MK iterations: 19006
UUID: 1da14492-aec4-4924-905d-e5aa28cbcff4
Key Slot 0: ENABLED
Iterations: 296206
Salt: 06 af 5b fc 27 a3 3c 84 02 d8 1e 89 ec fc c9 15
d8 c4 5e 3c 58 9b 92 0a e3 e5 48 5d 6b da cf 65
Key material offset: 8
AF stripes: 4000
Key Slot 1: ENABLED
Iterations: 729190
Salt: 3b a3 55 c0 5a d6 d0 0f 26 84 84 c4 a7 d1 83 23
9c 2d 6d ea 9f 76 83 04 36 8b d4 d6 19 07 ba 10
Key material offset: 264
AF stripes: 4000
Key Slot 2: DISABLED
Key Slot 3: DISABLED
Key Slot 4: DISABLED
Key Slot 5: DISABLED
Key Slot 6: DISABLED
Key Slot 7: DISABLED
As you see now we have one more key slot added and is enabled. We will use this key to auto mount LUKS device.
"cryptsetup luksRemoveKey /dev/device" where the device or partition will be /dev/sdb1 for our demo.Now let us create a key file which will be used to get the LUKS passphrase while booting the system. So at the reboot stage the system will not halt asking for passphrase and will get the key to auto mount LUKS device from this key file and continue to boot without password.
To create a key file execute the below command. Here my key file "lukskey" will be available under /root
[root@node1 ~]# dd if=/dev/random bs=32 count=1 of=/root/lukskey 1+0 records in 1+0 records out 32 bytes (32 B) copied, 0.000294018 s, 109 kB/s
To check the content of the lukskey file use xxd. As you see it is filled with random data.
[root@node1 ~]# xxd /root/lukskey 0000000: cd37 d965 8eb6 e1cd b009 467f 524b bf8e .7.e......F.RK.. 0000010: 5a53 7250 19c0 78b5 6d68 3f9c c8b6 6bf9 ZSrP..x.mh?...k.
Now let us add this key to our LUKS device
[root@node1 ~]# cryptsetup luksAddKey /dev/sdb1 /root/lukskey Enter any existing passphrase:
Verify the new keyslot. Now we have a new keyslot enabled.
[root@node1 ~]# cryptsetup luksDump /dev/sdb1
LUKS header information for /dev/sdb1
Version: 1
Cipher name: aes
Cipher mode: xts-plain64
Hash spec: sha256
Payload offset: 4096
MK bits: 256
MK digest: 4f 28 47 d0 91 cd 30 1f c0 78 73 b9 0e 83 cd d6 77 99 bf c8
MK salt: dc 91 2a 87 49 44 a9 2a 75 f7 f4 18 ee 39 54 e2
2f 72 e0 21 ba 07 59 84 75 58 c6 a9 ad 7e 43 ae
MK iterations: 19006
UUID: 1da14492-aec4-4924-905d-e5aa28cbcff4
Key Slot 0: ENABLED
Iterations: 296206
Salt: 06 af 5b fc 27 a3 3c 84 02 d8 1e 89 ec fc c9 15
d8 c4 5e 3c 58 9b 92 0a e3 e5 48 5d 6b da cf 65
Key material offset: 8
AF stripes: 4000
Key Slot 1: ENABLED
Iterations: 729190
Salt: 3b a3 55 c0 5a d6 d0 0f 26 84 84 c4 a7 d1 83 23
9c 2d 6d ea 9f 76 83 04 36 8b d4 d6 19 07 ba 10
Key material offset: 264
AF stripes: 4000
Key Slot 2: ENABLED
Iterations: 683556
Salt: 1a 13 aa 01 e1 c2 71 33 29 5f ae fc 25 71 2e c8
9f 9f 85 df 4b 80 61 4d 8d 52 35 7c 66 0a d0 af
Key material offset: 520
AF stripes: 4000
Key Slot 3: DISABLED
Key Slot 4: DISABLED
Key Slot 5: DISABLED
Key Slot 6: DISABLED
Key Slot 7: DISABLED
Next modify your crypttab and provide the keyfile details to make sure system does not halts asking for passphrase of luks device.
[root@node1 ~]# vim /etc/crypttab secret /dev/sdb1 /root/lukskey
Next reboot your node
[root@node1 ~]# reboot
I am sure this time your system should come up automatically without prompting for any passphrase to mount the LUKS encrypted partition.
Post reboot I will validate my mounted file system and I see as expected /secret is already in mounted state
[root@node1 ~]# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/centos-root 25G 3.8G 20G 16% /
devtmpfs 1.9G 0 1.9G 0% /dev
tmpfs 1.9G 0 1.9G 0% /dev/shm
tmpfs 1.9G 9.2M 1.9G 1% /run
tmpfs 1.9G 0 1.9G 0% /sys/fs/cgroup
/dev/sda1 488M 134M 319M 30% /boot
/dev/mapper/secret 4.8G 20M 4.6G 1% /secret
tmpfs 379M 8.0K 379M 1% /run/user/42
tmpfs 379M 0 379M 0% /run/user/0
In coming articles I will share the steps to extend or shrink (resize) LUKS encrypted partition in Linux.
Lastly I hope the steps from the article to auto mount LUKS device using fstab to boot with LUKS passphrase and with LUKS key on Linux was helpful. So, let me know your suggestions and feedback using the comment section.
References:
An overview on LUKS encryption
No. Don’t use on Kubuntu/Ubuntu 24.04, it will forward you to busybox and you will need to recover system with the manualy opening your luks root device.
Here is missing all about the initrams update which is required.
Hi there. I want to install case “Auto mount encrypted partition using fstab without key (prompts for LUKS passphrase)”
However, my os crashes a bit after entering a password during boot. As i understand fstab doesn’t know when it will obtain unencrypted mapped partition.
x-systemd.device-timeout for my encrypted ext4 doesn’t help much. What else might went wrong on ubuntu 22.04?
Best tutorial I have found for automounting luks drives! Thanks for sharing!
Just in case: I had the problem that the devices from time to time didn’t automount correctly while booting. Problem was that sometimes it happened, that my system hdd was mounted as
sdband notsdaand one of my external hdds were not mounted at all. My solution to this is to use the UUID infstabandcrypttab.If you encounter the problem: mount the encrypted devices manually and run:
In my case:
There you see the UUIDs of the decrypted partitions (“TYPE=”crypto_LUKS”)and the UUIDs of the filesystems (TYPE=”ext4″)
Put the
TYPE="ext4"UUIDs in/etc/fstaband theType="crypto_LUKS"in/etc/crypttabIn my case fstab looks like this:
and crypttab:
This solved my issue. Hope that this helps someone out there….See you space cowboys…
Sorry for the bad formatting 😉
Thank You for sharing. The least I can do is fix the formatting 🙂
and i forgot.. for anyone, who does not wanne use the cmd line, use “gnome-disks” for encrypting your drive, way easier for users.
oh.. ahm.. how to say this politly.. you do not store password in cmd lines, use this:
cat password.file | cryptsetup …
because it apears in “ps auxf ” and can be seen by any process,
and i hope you encrypted the disk this is run on, or your security model just broke.
Backups to unencrypted disks are done by creating a luks container on the drive, open it, format it, and copy the data into the container, close it, which makes it secure 😉
Hello there. Nice tutorial, thanks
I would like Linux completely forget encrypted disk connected during the boot (not asking any password nor picking the password somewhere) as with my scritp (see below) I can do it when I want (i.e. at certain backup time when my NAS gets connected). Is it any way I can have Linux not paying attention nor request password for an encrypted device at the boot ? That would be magic !
Here is my scripts:
Please check this article if it covers your use case
https://www.golinuxcloud.com/network-bound-disk-encryption-tang-clevis/
It is a good solution but I want encryption of my external hdd on client side be active always with the exception of the time frame while the nas performs its backup (to the unencrypted hdd on the client).
I don’t believe, also, Synology nas can act the way you described the server.
It looks too complicated. Need to investigate if I can load encryption modules on the fly and not at the beginning of boot process (simply adding few commands into my script)
Thanks
Please do share your observations, as I remember someone else had similar requirements for external disk. Unfortunately I have not been able to test this myself, will add it to my todo lists and if I can test this sometime then will create a new article.