PASSWD(1) User Commands PASSWD(1)


passwd - 更改用户密码


passwd [options] [LOGIN]


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



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.


Then, the password is tested for complexity. passwd will reject any password which is not suitably complex. Care must be taken not to include the system default erase or kill characters.


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.


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


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


-e, --expire


-h, --help


-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


-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 set the account's expire date to Jan 2, 1970).


-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


-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.

-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. PAM authentication is using the host files. No SELINUX support.

-S, --status

显示账户状态信息。状态信息包含 7 个字段。首个字段是用户的登录名,第二个字段表示用户账户是否已经锁定密码(L)、没有密码 (NP)或者密码可用(P),第三个字段给出最后一次更改密码的日期。接下来的四个字段分别是密码的最小年龄、最大年龄、警告期和禁用期。这些年龄以天为单位计算。

-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 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.


在启动了 NIS 的系统上,如果没有登录 NIS 服务器,用户或许不能更改自己的密码。

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







PAM configuration for passwd.


The passwd command exits with the following values:




permission denied


invalid combination of options


unexpected failure, nothing done


unexpected failure, passwd file missing


passwd file busy, try again


invalid argument to option


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: ""

2024-04-01 shadow-utils 4.15.1