Linux: Mount second encrypted HDD automatically without entering a password

This is one possibility to do this. There are other and maybe even better ways to do this.

1. Generate a key for your encrypted harddisk:

   Copydd if=/dev/random of=/home/bob/keyfile_sdb1 bs=4096 count=1
   

2. Then add your keyfile to encrypted harddisk: How to change your dm-crypt passphrase (step 3)

3. Create a mountpoint:

   Copymkdir /mnt/space
   

4. Create a script e.g. in your homedirectory (/home/bob/mount_sdb1.sh):

   Copy#!bin/bash
   
   #open harddisk
   sudo /sbin/cryptsetup --key-file /home/bob/keyfile_sdb1 luksOpen /dev/sdb1 sdb1_crypt
   #mount decrypted harddisk
   sudo /bin/mount /dev/mapper/sdb1_crypt /mnt/space
   

5. Add this line to your /etc/sudoers that you must not enter a password

   Copy%admin ALL=(ALL) NOPASSWD:/sbin/cryptsetup, /bin/mount    
   

6. Add this script to "System - Einstellungen - Startprogramme"

After rebooting the harddisk should be mounted automatically