PASSWD(1)

名称
passwd - 更改用户密码

大纲

passwd [options] [LOGIN]

描述

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.

  密码更改

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.

  关于用户密码的提示

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

选项

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
    让一个账户的密码立即过期。这可以强制一个用户下次登录时更改密码。

-h, --help
    显示帮助信息并退出。

-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
    表示密码更改只应该因为认证口令(密码)过期更改。用户希望保持他们尚未过期的口令。

-l, --lock
    锁定指定账户的密码。此选项通过将密码更改为一个不可能与加密值匹配的值来禁用(它在密码开头添加一个“!”)。

    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).

    被锁定了密码的用户不允许更改密码。

-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
    安静模式。

-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. No PAM support. 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 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.

CAVEATS

密码复杂性检查在每台机器间不同。用户应该选择适合的尽量复杂的密码。

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.

文件

/etc/passwd
    用户账户信息。

/etc/shadow
    安全用户账户信息。

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

退出值

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)

参见

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/"