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I am superadmin of a server and like to change password of an existing user . How can I do that ?

I tried

usermod -p 'new-password' john

but it didn't worked ?

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the best answer is here: askubuntu.com/a/80447/55435, note to checkout the comments as well – ryenus Jun 30 '15 at 4:03
up vote 3 down vote accepted

You may use passwd:

sudo passwd USERNAME 

You need not sudo if you're superuser yourself

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sudo require root password :) – Achu May 13 '12 at 18:41
    
@Achu: it's required current user password. But he is superuser. – RiaD May 13 '12 at 19:31
    
What does superuser represent? – Achu May 13 '12 at 19:37

The usermod -p flag is expecting the data to be the password already in an encrypted format.

Use openssl passwd to generate the encrypted data, or do it like this:

usermod -p `openssl passwd` (USERNAME)
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The reason it didn't work is because usermod's -p option expects the password to be encrypted already.

From usermod's man page:

 -p, --password PASSWORD
       The encrypted password, as returned by crypt(3).

To set a password in this way is not recommended.

Instead You should use passwd <username>. This should (as usermod) be done as root (if you're not changing the currently logged in users password).

To change the password for user foo.

sudo passwd foo

This will prompt for a new password.

Have a look at the man-page for passwd for more info on setting for example expire time.

Good Luck!

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Just type

passwd

In this way normal user can change own password without root privilege if you don't have.

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The way to assign a password with usermod (which is what the OP actually asked for) is to use a crypt() hashed password for the -p argument.

SALT="Q9"
PLAINTEXT="secret_password"
HASH=$(perl -e "print crypt(${PLAINTEXT},${SALT})")
echo "Password Hash = \"${HASH}\""

Then use that in your usermod -p command line argument:

usermod -p ${HASH} john
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A non-interactive single line command for changing the password of a user:

sudo usermod -p `perl -e "print crypt("new-password","Q4")"` john

usermod -p requires encrypted password to work. Please note the new-password will be visible for users who can list the processes.

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