PASSWD(1)

NAME
passwd, yppasswd - modify a user's password

SYNOPSIS
passwd [-l] [user]
yppasswd [-l] [-y] [-d domain] [-h host] [-o]

DESCRIPTION
The passwd utility changes the user's local, Kerberos, or NIS password. If the user is not the super-user, passwd first prompts for the current password and will not continue unless the correct password is entered.

When entering the new password, the characters entered do not echo, in order to avoid the password being seen by a passer-by. The passwd utility prompts for the new password twice in order to detect typing errors.

The new password should be at least six characters long (which may be overridden using the login.conf(5) “minpasswordlen” setting for a user's login class) and not purely alphabetic. Its total length must be less than _PASSWORD_LEN (currently 128 characters).

The new password should contain a mixture of upper and lower case characters (which may be overridden using the login.conf(5) “mixpasswordcase” setting for a user's login class). Allowing lower case passwords may be useful where the password file will be used in situations where only lower case passwords are permissible, such as when using Samba to authenticate Windows clients. In all other situations, numbers, upper case letters and meta characters are encouraged.

Once the password has been verified, passwd communicates the new password information to the Kerberos authenticating host.

The following option is available:

-l  Cause the password to be updated only in the local password file, and not with the Kerberos database. When changing only the local password, pwd_mkdb(8) is used to update the password databases.

When changing local or NIS password, the next password change date is set according to “passwordtime” capability in the user's login class.

To change another user's Kerberos password, one must first run kinit(1) (security/heimdal) followed by passwd. The super-user is not required to provide a user's current password if only the local password is modified.

NIS INTERACTION
The passwd utility has built-in support for NIS. If a user exists in the NIS password database but does not exist locally, passwd automatically switches into yppasswd mode. If the specified user does not exist in either the local password database or the NIS password maps, passwd returns an error.

When changing an NIS password, unprivileged users are required to provide their old password for authentication (the rpc.yppasswdd(8) daemon requires the original password before it will allow any changes to the NIS password maps). This restriction applies even to the super-user, with one important exception: the password authentication is bypassed for the super-user on the NIS master server. This means that the super-user on the NIS master server can make unrestricted changes to anyone's NIS password. The super-user on NIS client systems and NIS slave servers still needs to provide a password before the update will be processed.

The following additional options are supported for use with NIS:

-y  Override passwd's checking heuristics and forces it into NIS mode.

-l  When NIS is enabled, the -l flag can be used to force passwd into “local only” mode. This flag can be used to change the entry for a local user when an NIS user exists with the same login name. For example, you will sometimes find entries for system “placeholder” users such as bin or daemon in both the NIS password maps and the local user database. By default, passwd will try to change the NIS password. The -l flag can be used to change the local password instead.

-d domain
    Specify what domain to use when changing an NIS password. By default, passwd assumes that the system default domain should be used. This flag is primarily for use by the superuser on the NIS master server: a single NIS server can support multiple domains. It is also possible that the domainname on the NIS master may not be set (it is not necessary for an NIS server to also be a client) in which case the passwd command needs to be told what domain to operate on.

-h host
    Specify the name of an NIS server. This option, in conjunction with the -d option, can be used to change an NIS password on a non-local NIS server. When a domain is specified with the -d option and passwd is unable to determine the name of the NIS master server (possibly because the local domainname is not set), the name of the NIS master is assumed to be “localhost”. This can be overridden with the -h flag. The specified hostname need not be the name of an NIS master: the name of the NIS master for a given map can be determined by querying any NIS server (master or slave) in a domain, so specifying the name of a slave server will work equally well.

-o  Do not automatically override the password authentication checks for the super-user on the NIS master server; assume “old” mode instead. This flag is of limited practical use but is useful for testing.

FILES
/etc/master.passwd
    the user database
/etc/passwd
    a Version 7 format password file
/etc/passwd.XXXXXX
    temporary copy of the password file
/etc/login.conf
    login class capabilities database
/etc/auth.conf
    configure authentication services

SEE ALSO
chpass(1), kinit(1), login(1), login.conf(5), passwd(5), kerberos(8) (security/heimdal), kpasswdd(8) (security/heimdal), pw(8), pwd_mkdb(8), vipw(8) Robert Morris, Ken Thompson, UNIX password security.

NOTES
The yppasswd command is really only a link to passwd.

HISTORY
A passwd command appeared in AT&T UNIX.