How to set a new password from bash?

Question

I'm using busybox with a limited passwd (I don't have --stdin option) and without chpasswd and I need to change the password of an user from bash. Here is my best result:

echo newpassword > pwdfile
echo newpassword > pwdfile
cat pwdfile | passwd myuser
Changing password for myuser
Enter the new password (minimum of 5, maximum of 8 characters)
Please use a combination of upper and lower case letters and numbers.
Enter new password:
Bad password: too simple.

Warning: weak password (continuing).
Re-enter new password:
passwd: The password for myuser is unchanged.

Solution

Busybox has chpasswd(8) which is a utility best used to create/update a lot of users very quickly and with one command. It accepts data from STDIN in username:password form. That means that you can do something like this:

$ cat pwdfile | chpasswd

or

$ < pwdfile chpasswd

Note that pwdfile must have username:new_password syntax.

Then again, you could always edit /etc/shadow yourself -- but please don't.

Comments

[clerksx]

There's no need to cat to a pipe, just use IO redirection; < pwdfile chpasswd.

[michelemarcon]

My busybox does not have chpasswd.

[michelemarcon]

passwd: invalid option -- - BusyBox v1.00 (2011.04.28-16:58+0000) multi-call binary Usage: passwd [OPTION] [name] Change a user password. If no name is specified, changes the password for the current user. Options: -a Define which algorithm shall be used for the password (Choices: des, md5) -d Delete the password for the specified user account -l Locks (disables) the specified user account -u Unlocks (re-enables) the specified user account

[n0pe]

Is the user you're changing the password for in both /etc/passwd and /etc/shadow?

[michelemarcon]

Yes, it is present on both files. The user can log in and out normally.

[n0pe]

Can you try with a non-weak password? Maybe that's the issue.