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NAME | SYNOPSIS | DESCRIPTION | OPTIONS | CAVEATS | FILES | EXIT VALUES | SEE ALSO | COLOPHON |
PASSWD(1) User Commands PASSWD(1)
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.
Password Changes
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:
· lower case alphabetics
· digits 0 thru 9
· 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
complex.
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 advice on how to choose a strong password on
http://en.wikipedia.org/wiki/Password_strength
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 his/her 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 set 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 his/her 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.
-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 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
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.
/etc/passwd
User account information.
/etc/shadow
Secure user account information.
/etc/pam.d/passwd
PAM configuration for passwd.
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
chpasswd(8), passwd(5), shadow(5), usermod(8).
This page is part of the shadow-utils (utilities for managing
accounts and shadow password files) project. Information about the
project can be found at ⟨http://pkg-shadow.alioth.debian.org/⟩. If
you have a bug report for this manual page, see
⟨http://pkg-shadow.alioth.debian.org/getinvolved.php⟩. This page was
obtained from the project's upstream Git repository
⟨git://anonscm.debian.org/git/pkg-shadow/shadow.git⟩ on 2017-07-05.
If you discover any rendering problems in this HTML version of the
page, or you believe there is a better or more up-to-date source for
the page, or you have corrections or improvements to the information
in this COLOPHON (which is not part of the original manual page),
send a mail to man-pages@man7.org
shadow-utils 4.4 07/05/2017 PASSWD(1)
Pages that refer to this page: ldappasswd(1), login(1), login(1@@shadow-utils), crypt(3), pts(4), login.defs(5), passwd(5), passwd(5@@shadow-utils), shadow(5), chpasswd(8), groupadd(8), groupdel(8), groupmems(8), groupmod(8), newusers(8), useradd(8), userdel(8), usermod(8), vipw(8@@util-linux)