PASSWD(1) User Commands PASSWD(1)
NAME
passwd - change user password
SYNOPSIS
passwd [options] [LOGIN]
DESCRIPTION
The passwd command changes passwords for user accounts. A normal user
may only change the password for their own account, while the superuser
may change the password for any account. passwd also changes the
account or associated password validity period.
Password Changes
The user is first prompted for their 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 superuser is permitted to bypass this step so that forgotten
passwords may be changed.
After the password has been entered, password aging information is
checked to see if the user is permitted to change the password at this
time. If not, passwd refuses to change the password and exits.
The user is then prompted twice for a replacement password. The second
entry is compared against the first and both are required to match in
order for the password to be changed.
Then, the password is tested for complexity. passwd will reject any
password which is not suitably complex. Care must be taken not to
include the system default erase or kill characters.
Hints for user passwords
The security of a password depends upon the strength of the encryption
algorithm and the size of the key space. The legacy UNIX System
encryption method is based on the NBS DES algorithm. More recent methods
are now recommended (see ENCRYPT_METHOD). The size of the key space
depends upon the randomness of the password which is selected.
Compromises in password security normally result from careless password
selection or handling. For this reason, you should not select a password
which appears in a dictionary or which must be written down. The
password should also not be a proper name, your license number, birth
date, or street address. Any of these may be used as guesses to violate
system security.
As a general guideline, passwords should be long and random. It's fine
to use simple character sets, such as passwords consisting only of
lowercase letters, if that helps memorizing longer passwords. For a
password consisting only of lowercase English letters randomly chosen,
and a length of 32, there are 26^32 (approximately 2^150) different
possible combinations. Being an exponential equation, it's apparent that
the exponent (the length) is more important than the base (the size of
the character set).
You can find advice on how to choose a strong password on
https://en.wikipedia.org/wiki/Password_strength
OPTIONS
The options which apply to the passwd command are:
-a, --all
This option can be used only with -S and causes show status for all
users.
-d, --delete
Delete a user's password (make it empty). This is a quick way to
disable a password for an account. It will set the named account
passwordless.
-e, --expire
Immediately expire an account's password. This in effect can force a
user to change their password at the user's next login.
-h, --help
Display help message and exit.
-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 INACTIVE days, the user may no longer sign on
to the account.
-k, --keep-tokens
Indicate password change should be performed only for expired
authentication tokens (passwords). The user wishes to keep their
non-expired tokens as before.
-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 adds a ´!´ at the beginning of the password).
Note that this does not disable the account. The user may still be
able to login using another authentication token (e.g. an SSH key).
To disable the account, administrators should use usermod
--expiredate 1 (this sets the account's expire date to 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
their password at any time.
-q, --quiet
Quiet mode.
-r, --repository REPOSITORY
change password in REPOSITORY repository
-R, --root CHROOT_DIR
Apply changes in the CHROOT_DIR directory and use the configuration
files from the CHROOT_DIR directory. Only absolute paths are
supported.
-P, --prefix PREFIX_DIR
Apply changes to configuration files under the root filesystem found
under the directory PREFIX_DIR. This option does not chroot and is
intended for preparing a cross-compilation target. Some limitations:
NIS and LDAP users/groups are not verified. No PAM support. No
SELINUX support.
-S, --status
Display account status information. The status information consists
of 7 fields. The first field is the user's login name. The second
field indicates if the user account has a locked password (L), has
no password (NP), or has a usable password (P). The third field
gives the date of the last password change. The next four fields are
the minimum age, maximum age, warning period, and inactivity period
for the password. These ages are expressed in days.
-u, --unlock
Unlock the password of the named account. This option re-enables a
password by changing the password back to its previous value (to the
value before using the -l option).
-w, --warndays WARN_DAYS
Set the number of days of warning before a password change is
required. The WARN_DAYS option 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 is required to be changed.
Passing the number -1 as MAX_DAYS will remove checking a password's
validity.
-s, --stdin
This option is used to indicate that passwd should read the new
password from standard input, which can be a pipe.
CAVEATS
Password complexity checking may vary from site to site. The user is
urged to select a password as complex as he or she feels comfortable
with.
Users may not be able to change their password on a system if NIS is
enabled and they are not logged into the NIS server.
passwd uses PAM to authenticate users and to change their passwords.
FILES
/etc/passwd
User account information.
/etc/shadow
Secure user account information.
/etc/pam.d/passwd
PAM configuration for passwd.
EXIT VALUES
The passwd command exits with the following values:
0
success
1
permission denied
2
invalid combination of options
3
unexpected failure, nothing done
4
unexpected failure, passwd file missing
5
passwd file busy, try again
6
invalid argument to option
SEE ALSO
chpasswd(8), makepasswd(1), passwd(5), shadow(5), usermod(8).
The following web page comically (yet correctly) compares the strength
of two different methods for choosing a password:
"https://xkcd.com/936/"
shadow-utils 4.17.4 04/19/2025 PASSWD(1)
Generated by dwww version 1.16 on Fri Dec 5 18:08:14 CET 2025.