PASSWD(1) | User Commands | 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
-d, --delete
-e, --expire
-h, --help
-i, --inactive INACTIVE
-k, --keep-tokens
-l, --lock
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
-q, --quiet
-r, --repository REPOSITORY
-R, --root CHROOT_DIR
-P, --prefix PREFIX_DIR
-S, --status
-u, --unlock
-w, --warndays WARN_DAYS
-x, --maxdays MAX_DAYS
Passing the number -1 as MAX_DAYS will remove checking a password's validity.
-s, --stdin
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
/etc/shadow
/etc/pam.d/passwd
VALORI RESTITUITI
The passwd command exits with the following values:
0
1
2
3
4
5
6
10
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/"
27/06/2025 | shadow-utils 4.18.0 |