Provided by: passwd_184.108.40.206+svn3283-3ubuntu5_i386
passwd - change user password
passwd [options] [LOGIN]
The passwd command changes passwords for user accounts. A normal user
may only change the password for his/her own account, while the
superuser may change the password for any account. passwd also changes
the account or associated password validity period.
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 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. As a general guideline,
passwords should consist of 6 to 8 characters including one or more
characters from each of the following sets:
o lower case alphabetics
o digits 0 thru 9
o punctuation marks
Care must be taken not to include the system default erase or kill
characters. passwd will reject any password which is not suitably
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.
You can find advices on how to choose a strong password on
The options which apply to the passwd command are:
This option can be used only with -S and causes show status for all
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
Immediately expire an account's password. This in effect can force
a user to change his/her password at the user's next login.
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.
Indicate password change should be performed only for expired
authentication tokens (passwords). The user wishes to keep their
non-expired tokens as before.
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 set the account's expire date to Jan 2, 1970).
Users with a locked password are not allowed to change their
-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.
-r, --repository REPOSITORY
change password in REPOSITORY repository
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.
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 his/her 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.
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
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.
User account information.
Secure user account information.
PAM configuration for passwd.
The passwd command exits with the following values:
invalid combination of options
unexpected failure, nothing done
unexpected failure, passwd file missing
passwd file busy, try again
invalid argument to option
passwd(5), shadow(5), usermod(8).