mount fail unknown filesystem type crypto_LUKS

Question

I am facing a problem where I cannot mount a filesystem following decryption. All online searches for advice I have seen basically lead me to do what I have already - Anyone got any ideas?

My initial steps to decrypt are as follows - I ran with debug and verbose and all output was fine, no errors or warnings

cryptsetup luksOpen /dev/sdb1 mydata
+entered passphrase

I then attempt to mount it Upon running command the error below occurs

[root@PRC01P ~]# mount /dev/sdb1 /mydata
mount: unknown filesystem type 'crypto_LUKS'

other info commands - if decryption was succesful should this still show as type crypto_LUKS??

[root@PRC01P ~]# lsblk -lf | grep LUKS
sdb1      crypto_LUKS

Here is lsblk on its own:

-bash-4.2$ lsblk
NAME          MAJ:MIN RM  SIZE RO TYPE  MOUNTPOINT
fd0             2:0    1    4K  0 disk
sda             8:0    0   30G  0 disk
├─sda1          8:1    0  500M  0 part  /boot
└─sda2          8:2    0 29.5G  0 part
  ├─rhel-root 253:0    0 26.5G  0 lvm   /
  └─rhel-swap 253:1    0    3G  0 lvm   [SWAP]
sdb             8:16   0   60G  0 disk
└─sdb1          8:17   0   60G  0 part
  └─mydata 253:2    0   60G  0 crypt
sdc             8:32   0    6G  0 disk
sr0            11:0    1 1024M  0 rom

Here is the result of a df:

-bash-4.2$ df
Filesystem            1K-blocks    Used Available Use% Mounted on
/dev/mapper/rhel-root  27781884 5977316  21804568  22% /
devtmpfs                1930032       0   1930032   0% /dev
tmpfs                   1940852       0   1940852   0% /dev/shm
tmpfs                   1940852   66176   1874676   4% /run
tmpfs                   1940852       0   1940852   0% /sys/fs/cgroup
/dev/sda1                508588  191448    317140  38% /boot
tmpfs                    388172       0    388172   0% /run/user/995
tmpfs                    388172       0    388172   0% /run/user/1002
tmpfs                    388172       0    388172   0% /run/user/1001

Thanks for any advice

Answer 1

The correct order is

1. cryptsetup luksOpen /dev/sdb1 mydata
   

   which will open the LUKS formatted device.  (You have to enter a password for the device.)

2. mount /dev/mapper/mydata /mydata
   

   which will map device to /mydata.

It might be a good idea to use different names, e.g.,

sudo cryptsetup luksOpen /dev/sda3 secure
sudo mount /dev/mapper/secure /home_secure

lsblk will list

(...)
sda          8:0    0 465,8G  0 disk
├─sda1       8:1    0   1,9G  0 part  /boot
├─sda2       8:2    0     1K  0 part
├─sda3       8:3    0 368,5G  0 part
│ └─secure 253:0    0 368,5G  0 crypt /home_secure
└─sda5       8:5    0  95,4G  0 part  /

---

To revert, using my sample names:

1. umount /home_secure
   

   be sure that no files are used in /home_secure;

2. then close the LUKS volume:

   cryptsetup close secure
   

Answer 2

You're trying to mount the wrong device.

cryptsetup luksOpen /dev/sdb1 mydata

With this, /dev/sdb1 is your encrypted LUKS device, and /dev/mapper/mydata is the decrypted contents.

mount /dev/sdb1 /mydata

This fails because you can't mount a LUKS device. LUKS is not a filesystem.

You have to mount the decrypted one:

mount /dev/mapper/mydata /mydata

...and this will only work if there's already a filesystem inside /dev/mapper/mydata (created with mkfs after luksFormat and luksOpen).