path: root/share/man/man5/passwd.5

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.\"     @(#)passwd.5	8.1 (Berkeley) 6/5/93
.\"
.Dd $Mdocdate: June 20 2012 $
.Dt PASSWD 5
.Os
.Sh NAME
.Nm passwd ,
.Nm master.passwd
.Nd format of the password file
.Sh DESCRIPTION
The
.Nm master.passwd
file, readable only by root, consists of newline-separated records,
one per user, containing ten colon separated fields.
These fields are as follows:
.Pp
.Bl -tag -width password -offset indent -compact
.It name
User's login name.
.It password
User's
.Em encrypted
password.
.It uid
User's login user ID.
.It gid
User's login group ID.
.It class
User's general classification (see
.Xr login.conf 5 ) .
.It change
Password change time.
.It expire
Account expiration time.
.It gecos
General information about the user.
.It home_dir
User's home directory.
.It shell
User's login shell.
.El
.Pp
The publicly-readable
.Nm passwd
file is generated from the
.Nm master.passwd
file by
.Xr pwd_mkdb 8
and has the class, change, and expire fields removed.
Also, the encrypted password field is replaced by an asterisk.
.Pp
The password files should never be edited by hand;
.Xr vipw 8
should be used instead.
.Pp
The
.Ar name
field is the login used to access the computer account, and the
.Ar uid
field is the number associated with it.
They should both be unique across the system (and often across a group of
systems) since they control file access.
.Pp
While it is possible to have multiple entries with identical login names
and/or identical user IDs, it is usually a mistake to do so.
Routines that manipulate these files will often return only one of the
multiple entries, and that one by random selection.
.Pp
The login name may be up to 31 characters long.
For compatibility with legacy software, a login name should start
with a letter and consist solely of letters, numbers, dashes and
underscores.
The login name must never begin with a dash
.Pq Ql \&- ;
also, it is strongly
suggested that neither uppercase characters nor dots
.Pq Ql \&.
be part of the name, as this tends to confuse mailers.
No field may contain a colon
as this has been used historically to separate the fields
in the user database.
.Pp
The password field is the
.Em encrypted
form of the password.
If the
.Ar password
field is empty, no password will be required to gain access to the machine.
This is almost invariably a mistake.
By convention, accounts that are not intended to be logged in to
(e.g. bin, daemon, sshd) only contain a single asterisk in the
.Ar password
field.
Note that there is nothing special about
.Ql * ,
it is just one of many characters that cannot occur in a
valid encrypted password
(see
.Xr crypt 3 ) .
Similarly, login accounts not allowing password authentication
but allowing other authentication methods, for example public key
authentication, conventionally have 13 asterisks in the
.Ar password
field.
Because
.Nm master.passwd
contains the encrypted user passwords, it should not be readable by anyone
without appropriate privileges.
.Pp
Which type of cipher is used to encrypt the password information
depends on the configuration in
.Xr login.conf 5 .
It can be different for local and YP passwords.
.Pp
The
.Ar group
field is the primary group that the user will be placed in upon login.
Note that the
.Xr group 5
file may grant the user access to supplementary groups.
.Pp
The
.Ar class
field is used by
.Xr login 1
and other programs to determine which entry in the
.Xr login.conf 5
database should be used.
.Pp
The
.Ar change
field is the number in seconds, GMT, from the Epoch, until the
password for the account must be changed.
This field may be left empty to turn off the password aging feature.
.Pp
The
.Ar expire
field is the number in seconds, GMT, from the Epoch, until the
account expires.
This field may be left empty to turn off the account aging feature.
.Pp
The
.Ar gecos
field normally contains comma separated subfields as follows:
.Pp
.Bl -tag -width office -offset indent -compact
.It name
User's full name.
.It office
User's office location.
.It wphone
User's work phone number.
.It hphone
User's home phone number.
.El
.Pp
The full name may contain an ampersand
.Pq Ql \&& ,
which will be replaced by the capitalized login name when the gecos field
is displayed or used by various programs such as
.Xr finger 1 ,
.Xr sendmail 8 ,
etc.
.Pp
The office and phone number subfields, if they exist, are used by the
.Xr finger 1
program and possibly by other applications.
.Pp
The
.Ar home_dir
field is the full path name of a directory to be used as the initial
working directory for the user's login shell.
Usually, it is owned by the user and by the user's primary
.Ar group .
.Pp
The
.Ar shell
field is the command interpreter the user prefers.
If there is nothing in the
.Ar shell
field, the default shell
.Pq Pa /bin/sh
is assumed.
Accounts that are not intended to be logged in to usually have
a shell of
.Pa /sbin/nologin .
.Sh YP SUPPORT
If YP is active, the
.Nm passwd
file also supports standard YP exclusions and inclusions, based on user
names and netgroups.
.Pp
Lines beginning with a
.Ql \&-
(minus sign) are entries marked as being excluded
from any following inclusions, which are marked with a
.Ql +
(plus sign).
.Pp
If the second character of the line is a
.Ql @
(at sign), the operation involves the user fields of all entries in the
netgroup specified by the remaining characters of the
.Ar name
field.
Otherwise, the remainder of the
.Ar name
field is assumed to be a specific user name.
.Pp
The
.Ql +
token may also be alone in the
.Ar name
field, which causes all users from the
.Pa passwd.byname
and
.Pa passwd.byuid
YP maps to be included.
.Pp
If the entry contains non-empty
.Ar uid
or
.Ar gid
fields, the specified numbers will override the information retrieved
from the YP maps.
Additionally, if the
.Ar gecos ,
.Ar dir ,
or
.Ar shell
entries contain text, it will override the information included via YP.
On some systems, the
.Ar passwd
field may also be overridden.
It is recommended that the standard way to enable YP passwd support in
.Pa /etc/master.passwd
is:
.Pp
+:*::::::::
.Pp
which after
.Xr pwd_mkdb 8
will result in
.Pa /etc/passwd
containing:
.Pp
+:*:0:0:::
.Pp
When YP is enabled but temporarily unavailable, login becomes impossible
for all users except those having an entry in the
.Xr netid 5
file.
.Sh SEE ALSO
.Xr chpass 1 ,
.Xr login 1 ,
.Xr passwd 1 ,
.Xr crypt 3 ,
.Xr getpwent 3 ,
.Xr login.conf 5 ,
.Xr netgroup 5 ,
.Xr netid 5 ,
.Xr adduser 8 ,
.Xr Makefile.yp 8 ,
.Xr pwd_mkdb 8 ,
.Xr vipw 8 ,
.Xr yp 8
.Pp
.%T "Managing NFS and NIS"
(O'Reilly & Associates)
.Sh STANDARDS
The password file format has changed since
.Bx 4.3 .
The following
.Xr awk 1
script can be used to convert your old-style password
file into a new style password file.
The additional fields
.Dq class ,
.Dq change ,
and
.Dq expire
are added, but are turned off by default.
To set
.Ar change
and
.Ar expire
use the current day in seconds from the Epoch plus the number of seconds
of offset desired.
.Bd -literal -offset indent
BEGIN { FS = ":"}
{ print $1 ":" $2 ":" $3 ":" $4 "::0:0:" $5 ":" $6 ":" $7 }
.Ed
.Sh HISTORY
A
.Nm passwd
file format first appeared in
.At v1 .
The gecos field first appeared in
.At v3 ;
since the same version, the passwords are encrypted.
The gid field first appeared in
.At v5 ;
the class, change and expire fields as well as the
.Nm master.passwd
file in
.Bx 4.3 Reno .
.Pp
The YP file format first appeared in SunOS.
.Sh CAVEATS
Placing YP exclusions in the file after any inclusions does not cancel
the earlier inclusions.