PASSWD(1)

NOME
passwd - cambia la password utente

SINOSSI

passwd [options] [LOGIN]

DESCRIZIONE

The passwd command changes passwords for user accounts. A regular user can only change the password for their own account, while the superuser can change the password for any account. The passwd also changes the account or associated password validity period.

  Modifiche delle password

If the account has a non-empty password, the user is first prompted to enter their current password. The entered password is encrypted and compared to the stored value. The user has only one attempt to enter the correct password. The superuser can bypass this step to allow changing forgotten passwords.

After the password has been entered, password aging information is checked to determine 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 for the password to be changed.

Then, the password is tested for complexity. passwd rejects passwords that do not meet the complexity requirements. Do not include the system default erase or kill characters.

  Suggerimenti per password utente

The security of a password depends on 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 on the randomness of the selected password.

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 one that 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

OPZIONI

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
    Deletes a user's password, making it empty. This command sets the account to be passwordless.

-e, --expire
    Fa scadere subito la password dell'utente. Il che ha l'effetto di forzare un cambio password al successivo accesso da parte dell'utente.

-h, --help
    Mostra un messaggio di aiuto ed esce.

-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
    Indica che il cambio password va effettuato solo per i token (password) di autenticazione scaduti. L'utente vuole mantenere inalterati i token non scaduti.

-l, --lock
    Blocca la password dell'account indicato. Questa opzione disabilita una password modificandola in modo che non corrisponda a nessun valore cifrato (aggiunge un «!» all'inizio della 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 1970-01-02).

    Gli utenti con password bloccata non la possono cambiare.

-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
    Modalità silenziosa.

-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. No SELINUX support.

-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
    Visualizza le informazioni sullo stato di un account. Lo stato consiste di 7 campi. Il primo campo è il nome dell'utente. Il secondo campo indica se l'account ha una password bloccata (L), non ha password (NP) o ha una password valida (P). Il terzo campo contiene la data di ultima modifica della password. I successivi quattro campi sono l'età minima, la massima, il periodo di avviso e quello di inattività. Queste età sono espresse in giorni.

-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 password expiration during which the user is 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.

AVVISI/CAVEAT

Il controllo della complessità delle password varia da sistema a sistema. All'utente è caldamente consigliato si utilizzare una password che ritenga sufficientemente complessa.

Gli utenti possono non essere in grado di cambiare la propria password se NIS è abilitato ed essi non sono collegati al server NIS.

passwd uses PAM to authenticate users and to change their passwords.

FILE

/etc/passwd
    Informazioni sugli account utente.

/etc/shadow
    Informazioni sicure sugli account utente.

/etc/pam.d/passwd
    PAM configuration for passwd.

VALORI RESTITUITI

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

10
    an error was returned by pam(3)

VEDERE ANCHE

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/"