x SuSE Linux 13.1-RELEASE x
x SuSE Linux 13.1-RELEASEx
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 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:
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
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 advices on how to choose a strong password on
http://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 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.
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.
CONFIGURATION
The following configuration variables in /etc/login.defs change the
behavior of this tool:
ENCRYPT_METHOD (string)
This defines the system default encryption algorithm for encrypting
passwords (if no algorithm are specified on the command line).
It can take one of these values: DES (default), MD5, SHA256,
SHA512.
Note: this parameter overrides the MD5_CRYPT_ENAB variable.
MD5_CRYPT_ENAB (boolean)
Indicate if passwords must be encrypted using the MD5-based
algorithm. If set to yes, new passwords will be encrypted using the
MD5-based algorithm compatible with the one used by recent releases
of FreeBSD. It supports passwords of unlimited length and longer
salt strings. Set to no if you need to copy encrypted passwords to
other systems which don't understand the new algorithm. Default is
no.
This variable is superseded by the ENCRYPT_METHOD variable or by
any command line option used to configure the encryption algorithm.
This variable is deprecated. You should use ENCRYPT_METHOD.
OBSCURE_CHECKS_ENAB (boolean)
Enable additional checks upon password changes.
PASS_ALWAYS_WARN (boolean)
Warn about weak passwords (but still allow them) if you are root.
PASS_CHANGE_TRIES (number)
Maximum number of attempts to change password if rejected (too
easy).
PASS_MAX_LEN (number), PASS_MIN_LEN (number)
Number of significant characters in the password for crypt().
PASS_MAX_LEN is 8 by default. Don't change unless your crypt() is
better. This is ignored if MD5_CRYPT_ENAB set to yes.
SHA_CRYPT_MIN_ROUNDS (number), SHA_CRYPT_MAX_ROUNDS (number)
When ENCRYPT_METHOD is set to SHA256 or SHA512, this defines the
number of SHA rounds used by the encryption algorithm by default
(when the number of rounds is not specified on the command line).
With a lot of rounds, it is more difficult to brute forcing the
password. But note also that more CPU resources will be needed to
authenticate users.
If not specified, the libc will choose the default number of rounds
(5000).
The values must be inside the 1000-999,999,999 range.
If only one of the SHA_CRYPT_MIN_ROUNDS or SHA_CRYPT_MAX_ROUNDS
values is set, then this value will be used.
If SHA_CRYPT_MIN_ROUNDS > SHA_CRYPT_MAX_ROUNDS, the highest value
will be used.
FILES
/etc/passwd
User account information.
/etc/shadow
Secure user account information.
/etc/login.defs
Shadow password suite configuration.
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), passwd(5), shadow(5), login.defs(5), usermod(8).
shadow-utils 4.1.5.1 05/25/2012 PASSWD(1)
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