Why am I getting locked out or no longer able to change my root password after upgrading firmware on a Digi CM?

This problem only occurs when upgrading from very early (pre-1.1.0) Digi CM firmware to anything newer.

The problem is caused by the addition of Shadow Password support, which occured in the 1.1.0 release. Here are three methods to resolve this issue:
 

To activate shadow password, you can select one of following methods after firmware upgrade.

< Method 1>

Do a Factory Reset.
(either using Factory reset switch or by selecting Factory reset using the Web UI 
or console menu) This is the easiest way, but all previous configurations will be
restored to factory default values.

< Method 2>

Step 1. Log in to the CLI as root
Step 2. Create an empty file called /etc/shadow.
       #cd /etc/
       #rm -rf shadow  (->remove default link file)
       #touch shadow
       #chmod 600 shadow
Step 3. Run following command to add temporary user.
       # useradd tempuser
Step 4. Edit /etc/shadow file.
        Replace "tempuser" with "root"
       #vi /etc/shadow
Step 5. Change root password
       #passwd 
        Enter new UNIX password:
        Retype new UNIX password:
Step 6. Change passwords of all other users using Web UI or console menu

 
< Method 3 >
Step 1. Log in to the CLI as root
Step 2. Create an empty file called /etc/shadow.
       #cd /etc/
       #rm -rf shadow
       #touch shadow
       #chmod 600 shadow
Step 3. Run following command to add temporary user.
       # useradd tempuser
Step 4. Edit /etc/shadow file.
        For each user in passwd file,
        Create a copy of the line that begins with "tempuser:"
        Then replace "tempuser" with the user name
       #vi /etc/shadow
Step 5. Change root password
       #passwd 
        Enter new UNIX password:
        Retype new UNIX password:
Step 6. Change passwords of all other users using passwd command in the CLI.
       #passwd admin
       Enter new UNIX password:
       Retype new UNIX password:
       #passwd padmin
       ...
       #passwd user1
Step 7. Rune ''''''''saveconf'''''''' command in the CLI
       #saveconf