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.\"	from: @(#)passwd.1	6.11 (Berkeley) 7/24/91
.\"
.Dd July 24, 1991
.Dt PASSWD 1
.Os
.Sh NAME
.Nm passwd
.Nd modify a user's password
.Sh SYNOPSIS
.Nm passwd
.Op Fl l
.Op Fl y
.Op Fl k
.Op Fl n Ar name
.Op Fl i Ar instance
.Op Fl r Ar realm
.Op Fl u Ar username[.instance][@realm]
.Op Ar user
.\" This should really be: passwd [-l] [-y] [-k [-n name] [-i instance] [-r realm] [-u username[.instance][@realm]]] [user]
.Sh DESCRIPTION
.Nm passwd
changes the user's local, Kerberos, or YP password.  First, the user is prompted
for their current password.
If the current password is correctly typed, a new password is
requested.
The new password must be entered twice to avoid typing errors.
.Pp
The new password should be at least six characters long and not
purely alphabetic.
Its total length must be less than
.Dv _PASSWORD_LEN
(currently 128 characters).
Numbers, upper case letters and meta-characters
are encouraged.
.Bl -tag -width flag
.It Fl l
Causes the password to be updated only in the local
password file.  When changing only the local password,
.Xr pwd_mkdb  8
is used to update the password databases.
.It Fl y
Forces the YP password database entry to be changed, even if
the user has an entry in the local database.  The
.Xr rpc.yppasswdd 8
daemon should be running on the YP master server.
.It Fl k
Forces the change to affect the Kerberos database, even
if the user has a password in the local database.
Once the password has been verified,
.Nm passwd
communicates the new password information to
the Kerberos authenticating host.
.El
.Pp
The following flags are only used when the
.Fl k
flag is specified:
.Bl -tag -width flag
.It Fl n Ar name
Specifies a
.Ar name
that will be used as the principal name rather  than  the  username
of the user running
.Nm passwd .
(This is determined from the ticket file  if  it exists;  otherwise,
it is determined from the Unix user ID.)
.It Fl i Ar instance
Specifies an
.Ar instance
to use rather than a null instance.
.It Fl r Ar realm
Specifies a
.Ar realm
instead of the local realm.
.It Fl u Ar username[.instance][@realm]
Specifies a fully qualified kerberos principal.
.El
.Pp
This is the behavior if no flags are specified:
if Kerberos is active then
.Nm passwd
will talk to the Kerberos server (even if the user has an entry
in the local database).
If the password is not in the local password database, then
an attempt is made to use the YP database.
.Pp
To change another user's Kerberos password, one must first
run
.Xr kinit 1
followed by
.Xr passwd 1 .
The super-user is not required to provide a user's current password
if only the local password is modified.
.Pp
Which type of cipher is used to encrypt the password information
depends on the configuration in
.Xr passwd.conf 5 .
It can be different for local and YP passwords.
.Sh FILES
.Bl -tag -width /etc/master.passwd -compact
.It Pa /etc/master.passwd
user database
.It Pa /etc/passwd
a Version 7 format password file
.It Pa /etc/passwd.XXXXXX
temporary copy of the password file
.It /etc/passwd.conf
configuration options
.El
.Sh SEE ALSO
.Xr chpass 1 ,
.Xr kerberos 1 ,
.Xr kinit 1 ,
.Xr login 1 ,
.Xr passwd 5 ,
.Xr passwd.conf 5 ,
.Xr kpasswdd 8 ,
.Xr pwd_mkdb 8 ,
.Xr vipw 8
.Rs
.%A Robert Morris
.%A Ken Thompson
.%T "UNIX password security"
.Re
.Sh HISTORY
A
.Nm passwd
command appeared in
.At v6 .