Linux and Unix passwd command

passwd commandOverview
passwd syntax
Quick Examples
Description
passwd examples
Related commands
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Overview

The passwd command is used to change the password of a user account. A normal user can run passwd to change their own 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.

passwd syntax

passwd [OPTION] [USER]

Quick Examples

Change Your Own Password

passwd

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

(current) UNIX password:

If it is correct, you will then be asked to enter a new password:

Enter new UNIX password:

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

Retype new UNIX password:

If the passwords match, the password will be changed.

Change Another User's Password

sudo passwd jeff

If you have superuser privileges, you can change another user's password. Here, we prefix the command with sudo to run it as the superuser. This command will change the password for user jeff. You will not be 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 will need to log in to the root account. To do this, you will need to know the password for user root.

Let's say your user name 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:

passwd sally

But what if you forgot the password for root as well? In this case, you will 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 will 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.

To boot into single-user mode, select Recovery Mode from the boot menu.

This will boot you into a text-only mode, and log you in as root.

If you need to mount /, do so:

mount -rw -o remount /

Now change sally's password:

passwd sally

Or root's:

passwd

When you're done, reboot your system:

shutdown -r now

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

Now that we've gone over the most common scenarios for using passwd, let's look at the command in more detail. The following sections will describe how the command works, how it can be used, and what options can be specified to make use of its different functions.

Description

The passwd command changes passwords for user accounts. A normal user can only change the password for their own 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 own 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 has been 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:

Options

The following options will change the way passwd operates:

-a, --all When used with -S (see below), this option will show the password status for all users. This option will not work if used without -S.
-d, --delete Delete a user's password (make it empty). This 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 has been expired for a number of 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 will set 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 will apply 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:

  1. The user's login name
  2. 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
  3. date of the last password change
  4. minimum password age
  5. maximum password age
  6. password warning period
  7. password inactivity period

In fields 4 through 7, password ages are expressed in days.

Specifying -a in addition to -S will display 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 prior to 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 will vary 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 into the NIS server.

System Files Used By Passwd

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

passwd examples

passwd

Change your own password.

sudo passwd username

Change the password for the user named username.

sudo passwd -S ted

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

ted P 05/13/2014 2 365 7 28

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.

sudo passwd -S -a

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

sudo passwd -l jane

Lock the password for user jane. She will be unable to log in until a system administrator unlocks it.

sudo passwd -u jane

Unlock jane's password. It will automatically be reset to whatever it was before it was locked, and she will be able to log in again.

sudo passwd -e alan

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

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.