Linux command with password

Linux passwd command

About passwd

On Unix-like operating systems, the passwd command is used to change the password of a user account. A normal user can run passwd to change their password, and a system administrator (the superuser) can use passwd to change another user’s password, or define how that account’s password can be used or changed.

This page covers the Linux version of passwd.

Description

The passwd command changes passwords for user accounts. A normal user can only change the password for their account, but the superuser can change the password for any account. passwd can also change or reset the account’s validity period — how much time can pass before the password expires and must be changed.

Before a normal user can change their password, they must first enter their current password for verification. (The superuser can bypass this step when changing another user’s password.)

After the current password is verified, passwd checks to see if the user is allowed to change their password at this time. If not, passwd refuses to continue, and exits.

Otherwise, the user is then prompted twice for a replacement password. Both entries must match for passwd to continue.

Next, the password is tested for complexity. As a general guideline, passwords should consist of at least 6 characters, including one or more of each of the following:

Syntax

Options

The following options change the way passwd operates:

-a, —all	When used with -S (see below), this option shows the password status for all users. This option won’t work if used without -S.
-d, —delete	Delete a user’s password (make it empty). This option is a quick way to disable logins for an account, without disabling the account itself.
-e, —expire	Immediately expire an account’s password. This forces a user to change their password the next time they log in.
-h, —help	Display information about how to use the passwd command.
-i, —inactive INACTIVE	This option is used to disable an account after the password was expired for many days. After a user account has had an expired password for integer INACTIVE days, the user may no longer sign on to the account.
-k, —keep-tokens	Keep password tokens. Indicates that this user’s password should only be changed if it has expired.
-l, —lock	Lock the password of the named account. This option disables a password by changing it to a value which matches no possible encrypted value. It does this by adding a character at the beginning of the encrypted password. Note that this does not disable the account. The user may still be able to log in using another authentication method (an SSH key, for example). To disable the account, the superuser can use the usermod command with the option —expiredate 1. This option sets the account’s expiration date to a date in the past — namely Jan 2, 1970. Users with a locked password are not allowed to change their password.
-n, —mindays MIN_DAYS	Set the minimum number of days between password changes to MIN_DAYS. A value of zero for this field indicates that the user may change his/her password at any time.
-q, —quiet	Quiet mode; passwd will operate without displaying any output.
-R, —root CHROOT_DIR	For advanced users: this option applies changes in the chroot directory CHROOT_DIR and use the configuration files from the CHROOT_DIR directory.
-S, —status	Display account status information. The status information consists of 7 fields: The user’s login name password usability: L if the account has a locked password, NP if the account has no password, or P if the account has a usable password date of the last password change minimum password age maximum password age password warning period password inactivity period In fields 4 through 7, password ages are expressed in days. Specifying -a in addition to -S displays password status for all users.
-u, —unlock	Unlock the password of the named account. This option re-enables a password by changing the password back to its value before the -l option was used to lock it.
-w, —warndays WARN_DAYS	Set the number of days of warning before a password change is required. WARN_DAYS is the number of days before the password expiring that a user will be warned that their password is about to expire.
-x, —maxdays MAX_DAYS	Set the maximum number of days a password remains valid. After MAX_DAYS, the password must be changed.

Notes

Password complexity varies depending on the system. Consult your operating system documentation for default complexity rules and how to change them.

On systems that use NIS (Network Information Services), users may not be able to change their password if they are not logged in to the NIS server.

Files used by passwd

/etc/passwd	User account information.
/etc/shadow	Secure user account information.
/etc/pam.d/passwd	PAM configuration for passwd.

Examples

Change your password

Running passwd with no options changes the password of the account running the command. You will first be prompted to enter the account’s current password:

If it is correct, you’ll be asked to enter a new password:

. and to enter the same password again, to verify it:

If the passwords match, the password will be changed.

Change another user’s password

If you have superuser privileges, you can change another user’s password. Here, we prefix the command with sudo to run as the superuser. This command changes the password for user jeff. You are not prompted for jeff‘s current password.

Change your password without knowing your current password

If you need to change your password because you forgot it, you need to log in to the root account. To do this, you need to know the password for user root.

Let’s say your username is sally, and you can’t remember your password. However, you have administrator access to the system: you can log in as root, using the password for that account. Log in as root, and then from the command line, run:

But what if you forgot the password for root as well? In this case, you need to log in to the machine in single-user mode, also known as runlevel 1. This cannot be done over the network, so you need physical access to the machine to boot into this runlevel.

Reboot the machine. When it is booting up, you should be presented with a bootloader menu. On many systems, such as Debian or Ubuntu, the boot menu will include an option for «Recovery Mode» or «Single User Mode» (as in the image below). Select this boot option.

This option boots you into a text-only mode, and log you in as root.

If you need to mount /, do so:

Now change sally‘s password:

When you’re done, reboot your system:

Start the system normally, and you should be able to log in as sally with the new password.

Additional examples

Check the status of the password for the user named ted. Output resembles the following:

Here, we see the user’s name (ted), followed by a P, indicating that his password is currently valid and usable. The password will expire on May 5, 2014. Ted cannot change his password more often than every 2 days, and must change the password every 365 days. He will be warned 7 days before a required password change, and if he allows his password to expire, his account will be disabled 28 days later.

Similar to the above command, but checks the password status for all user accounts, system-wide.

Lock the password for user jane. She cannot to log in until a system administrator unlocks it.

Unlock jane‘s password. It automatically resets to whatever it was before it was locked, and she can log in again.

Expire alan‘s password. The next time he logs in, he will be required to set a new password.

Related commands

chfn — Change a user’s finger information.
finger — List information about a user.
login — Begin a session on a system.
nispasswd — Change NIS+ password information.
nistbladm — Administer NIS+ tables.
useradd — Add a user to the system.
vipw — Safely edit the password file.
yppasswd — Change a network password in an NIS database.

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How To Linux Set or Change User Password

Linux Set User Password

Type following passwd command to change your own password:
$ passwd
Sample Outputs:

The user is first prompted for his/her old password if one is present. This password is then encrypted and compared against the stored password. The user has only one chance to enter the correct password. The super user is permitted to bypass this step so that forgotten passwords may be changed. A new password is tested for complexity. As a general guideline, passwords should consist of 10 to 20 characters including one or more from each of following sets:

1. Lower case alphabetics
2. Upper case alphabetics
3. Digits 0 thru 9
4. Punctuation marks/spacial characters

Linux change password for other user account

You need to login as the root user, type the following command to change password for user vivek:
# passwd vivek
OR
$ sudo passwd vivek
Sample putput:

• vivek – is username or account name.

Passwords do not display to the screen when you enter them. For example:

Linux changing user password using passwd

Linux Change Group Password

When the -g option is used, the password for the named group is changed. In this example, change password for group sales:
# passwd -g sales
The current group password is not prompted for. The -r option is used with the -g option to remove the current password from the named group. This allows group access to all members. The -R option is used with the -g option to restrict the named group for all users.

Changing user passwords on Linux

As a Linux system administrator (sysadmin) you can change password for any users on your server. To change a password on behalf of a user:

1. First sign on or “su” or “sudo” to the “root” account on Linux, run: sudo -i
2. Then type, passwd tom to change a password for tom user
3. The system will prompt you to enter a password twice

To change or set a new root (superuser) password type:
$ sudo passwd

Forcing Linux user to change password at their next login

By default, Linux passwords never expire for users. However, we can force users to change their password the next time they log in via GUI or CLI methods. The syntax is straightforward:
$ sudo passwd -e
$ sudo passwd —expire
Let us immediately expire an account’s password:
$ sudo passwd -e marlena
The system will confirm it:

When user try to login via ssh command, they will see the following on screen:

Locking and Unlocking user password of the named account

Note that the following local command does not disable the account. The user may still be able to login using another authentication token, such as an SSH key. To disable the account, administrators should use either usermod —expiredate 1 or sudo passwd —expire command. Also, users with a locked password are not allowed to change their password to get around the security policy set by sysadmin.

We can lock the password as follows:
$ sudo passwd -l
This option disables a password by changing it to a value which matches no possible encrypted value (it adds a ! at the beginning of the password in the /etc/shadow file. Want to unlock the password, try:
$ sudo passwd -u
The above command option re-enables a password by changing the password back to its previous value. In other words, to the value before using the -l option.

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A note about setting up a secure Linux password

Compromises in password security typically result from careless password selection. Avoid common password such as:

1. Words which appears in a dictionary
2. Your first and last name
3. Pet names
4. Kids or spouses names
5. License number
6. Date of birth (DoB)
7. Home or office address

I strongly recommend that you generate a unique password for all user accounts using your chosen password manager.

Conclusion

The passwd command line utility is used to update or change user’s password. The encrypted password is stored in /etc/shadow file and account information is in /etc/passwd file. To see all user account try grep command or cat command as follows:
$ cat /etc/passwd
$ grep ‘^userNameHere’ /etc/passwd
$ grep ‘^tom’ /etc/passwd
The guidance given in this quick tutorial should work with any Linux distribution, including Alpine, Arch, Ubuntu, Debian, RHEL, Fedora, Oracle CentOS, SUSE/OpenSUSE and other popular Linux distros.

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