The chpasswd command allows admins to change account passwords by piping username and password combinations to it.
This can be done one-account-at-a-time or by putting all of the accounts to be modified in a file and piping the file to the command.
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How to use chpasswd
Using the chpasswd command requires root privilege. You can switch to the root account and run a command like this:
# echo nemo:imafish | chpasswd
Better yet, you can use sudo with a command like this:
Source:: Network World – Linux