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PASSWD(5)                 FreeBSD File Formats Manual                PASSWD(5)

     passwd - format of the password file

     The passwd files are files consisting of newline separated records, one
     per user, containing ten colon (``:'') separated fields.  These fields
     are as follows:

           name      User's login name.

           password  User's encrypted password.

           uid       User's id.

           gid       User's login group id.

           class     User's login class.

           change    Password change time.

           expire    Account expiration time.

           gecos     General information about the user.

           home_dir  User's home directory.

           shell     User's login shell.

     Lines whose first non-whitespace character is a pound-sign (#) are
     comments, and are ignored.  Blank lines which consist only of spaces,
     tabs or newlines are also ignored.

     The name field is the login used to access the computer account, and the
     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.

     While it is possible to have multiple entries with identical login names
     and/or identical user id's, 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.

     The login name must never begin with a hyphen (``-''); also, it is
     strongly suggested that neither upper-case characters nor dots (``.'') 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.

     The password field is the encrypted form of the password.  If the
     password field is empty, no password will be required to gain access to
     the machine.  This is almost invariably a mistake.  Because these files
     contain the encrypted user passwords, they should not be readable by
     anyone without appropriate privileges.  Administrative accounts have a
     password field containing an asterisk `*' which disallows normal logins.

     The group field is the group that the user will be placed in upon login.
     Although this system supports multiple groups (see groups(1)) this field
     indicates the user's primary group.  Secondary group memberships are
     selected in /etc/group.

     The class field is a key for a user's login class.  Login classes are
     defined in login.conf(5), which is a termcap(5) style database of user
     attributes, accounting, resource and environment settings.

     The 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
     or set to 0 to turn off the password aging feature.

     The expire field is the number in seconds, GMT, from the epoch, until the
     account expires.  This field may be left empty or set to 0 to turn off
     the account aging feature.

     The gecos field normally contains comma (``,'') separated subfields as

           fullname       user's full name
           office         user's office location
           wphone         user's work phone number
           hphone         user's home phone number

     This information is used by the finger(1) program, and the first field
     used by the system mailer.  If an ampersand `&' character appears within
     the fullname field, programs that use this field will substitute it with
     a capitalized version of the account's login name.

     The user's home directory is the full UNIX path name where the user will
     be placed on login.

     The shell field is the command interpreter the user prefers.  If there is
     nothing in the shell field, the Bourne shell (/bin/sh) is assumed.  For
     security reasons, if the shell is set to a script that disallows access
     to the system (the nologin(8) script, for example), care should be taken
     not to import any environment variables.  With sh(1), this can be done by
     specifying the -p flag.  Check the specific shell documentation to
     determine how this is done with other shells.

   Enabling access to NIS passwd data
     The system administrator can configure FreeBSD to use NIS/YP for its
     password information by adding special records to the /etc/master.passwd
     file. These entries should be added with vipw(8) so that the changes can
     be properly merged with the hashed password databases and the /etc/passwd
     file ( /etc/passwd should never be edited manually). Alternatively, the
     administrator can modify /etc/master.passwd in some other way and then
     manually update the password databases with pwd_mkdb(8).

     The simplest way to activate NIS is to add an empty record with only a
     plus sign (`+') in the name field, such as this:


     The `+' will tell the getpwent(3) routines in FreeBSD's standard C
     library to begin using the NIS passwd maps for lookups.

     Note that the entry shown above is known as a wildcard entry, because it
     matches all users (the `+' without any other information matches
     everybody) and allows all NIS password data to be retrieved unaltered.
     However, by specifying a username or netgroup next to the `+' in the NIS
     entry, the administrator can affect what data are extracted from the NIS
     passwd maps and how it is interpreted. Here are a few example records
     that illustrate this feature (note that you can have several NIS entries
     in a single master.passwd file):


     Specific usernames are listed explicitly while netgroups are signified by
     a preceding `@'. In the above example, users in the ``staff'' and
     ``permitted-users'' netgroups will have their password information read
     from NIS and used unaltered. In other words, they will be allowed normal
     access to the machine. Users ``ken'' and ``dennis,'' who have been named
     explicitly rather than through a netgroup, will also have their password
     data read from NIS, _except_ that user ``ken'' will have his shell
     remapped to /bin/csh.  This means that value for his shell specified in
     the NIS password map will be overridden by the value specified in the
     special NIS entry in the local master.passwd file. User ``ken'' may have
     been assigned the csh shell because his NIS password entry specified a
     different shell that may not be installed on the client machine for
     political or technical reasons.  Meanwhile, users in the ``rejected-
     users'' netgroup are prevented from logging in because their UIDs, GIDs
     and shells have been overridden with invalid values.

     User ``mitnick'' will be be ignored entirely because his entry is
     specified with a `-' instead of a `+'. A minus entry can be used to block
     out certain NIS password entries completely; users who's password data
     has been excluded in this way are not recognized by the system at all.
     (Any overrides specified with minus entries are also ignored since there
     is no point in processing override information for a user that the system
     isn't going to recognize in the first place.)  In general, a minus entry
     is used to specifically exclude a user who might otherwise be granted
     access because he happens to be a member of an authorized netgroup. For
     example, if ``mitnick'' is a member of the ``permitted-users'' netgroup
     and must, for whatever the reason, be permitted to remain in that
     netgroup (possibly to retain access to other machines within the domain),
     the administrator can still deny him access to a particular system with a
     minus entry.  Also, it is sometimes easier to explicitly list those users
     who aren't allowed access rather than generate a possibly complicated
     list of users who are allowed access and omit the rest.

     Note that the plus and minus entries are evaluated in order from first to
     last with the first match taking precedence. This means the system will
     only use the first entry that matches a particular user.  If, for
     instance, we have a user ``foo'' who is a member of both the ``staff''
     netgroup and the ``rejected-users'' netgroup, he will be admitted to the
     system because the above example lists the entry for ``staff'' before the
     entry for ``rejected-users.'' If we reversed the order, user ``foo''
     would be flagged as a ``rejected-user'' instead and denied access.

     Lastly, any NIS password database records that do not match against at
     least one of the users or netgroups specified by the NIS access entries
     in the /etc/master.passwd file will be ignored (along with any users
     specified using minus entries). In our example shown above, we do not
     have a wildcard entry at the end of the list; therefore, the system will
     not recognize anyone except ``ken,'' ``dennis,'' the ``staff'' netgroup
     and the ``permitted-users'' netgroup as authorized users. The ``rejected-
     users'' netgroup will be recognized but all members will have their
     shells remapped and therefore be denied access.  All other NIS password
     records will be ignored. The administrator may add a wildcard entry to
     the end of the list such as:


     This entry acts as a catch-all for all users that don't match against any
     of the other entries.  /usr/local/bin/go_away can be a short shell script
     or program that prints a message telling the user that he is not allowed
     access to the system. This technique is sometimes useful when it is
     desirable to have the system be able to recognize all users in a
     particular NIS domain without necessarily granting them login access.
     See the above text on the shell field regarding security concerns when
     using a shell script as the login shell.

     The primary use of this override feature is to permit the administrator
     to enforce access restrictions on NIS client systems. Users can be
     granted access to one group of machines and denied access to other
     machines simply by adding or removing them from a particular netgroup.
     Since the netgroup database can also be accessed via NIS, this allows
     access restrictions to be administered from a single location, namely the
     NIS master server; once a host's access list has been set in
     /etc/master.passwd, it need not be modified again unless new netgroups
     are created.

   Shadow passwords through NIS
     FreeBSD uses a shadow password scheme: users' encrypted passwords are
     stored only in /etc/master.passwd and /etc/spwd.db, which are readable
     and writable only by the superuser. This is done to prevent users from
     running the encrypted passwords through password-guessing programs and
     gaining unauthorized access to other users' accounts. NIS does not
     support a standard means of password shadowing, which implies that
     placing your password data into the NIS passwd maps totally defeats the
     security of FreeBSD's password shadowing system.

     FreeBSD provides a few special features to help get around this problem.
     It is possible to implement password shadowing between FreeBSD NIS
     clients and FreeBSD NIS servers. The getpwent(3) routines will search for
     a master.passwd.byname and master.passwd.byuid maps which should contain
     the same data found in the /etc/master.passwd file. If the maps exist,
     FreeBSD will attempt to use them for user authentication instead of the
     standard passwd.byname and passwd.byuid maps.  FreeBSD's ypserv(8) will
     also check client requests to make sure they originate on a privileged
     port. Since only the superuser is allowed to bind to a privileged port,
     the server can tell if the requesting user is the superuser; all requests
     from non-privileged users to access the master.passwd maps will be
     refused. Since all user authentication programs run with superuser
     privilege, they should have the required access to users' encrypted
     password data while normal users will only be allowed access to the
     standard passwd maps which contain no password information.

     Note that this feature cannot be used in an environment with non-FreeBSD
     systems. Note also that a truly determined user with unrestricted access
     to your network could still compromise the master.passwd maps.

   UID and GID remapping with NIS overrides
     Unlike SunOS and other operating systems that use Sun's NIS code, FreeBSD
     allows the user to override all of the fields in a user's NIS passwd
     entry.  For example, consider the following /etc/master.passwd entry:

           +@foo-users:???:666:666:0:0:0:Bogus user:/home/bogus:/bin/bogus

     This entry will cause all users in the `foo-users' netgroup to have all
     of their password information overridden, including UIDs, GIDs and
     passwords. The result is that all `foo-users' will be locked out of the
     system, since their passwords will be remapped to invalid values.

     This is important to remember because most people are accustomed to using
     an NIS wildcard entry that looks like this:


     This often leads to new FreeBSD administrators choosing NIS entries for
     their master.passwd files that look like this:


     Or worse, this


     DO _NOT_ PUT ENTRIES LIKE THIS IN YOUR master.passwd FILE!! The first
     tells FreeBSD to remap all passwords to `*' (which will prevent anybody
     from logging in) and to remap all UIDs and GIDs to 0 (which will make
     everybody appear to be the superuser). The second case just maps all UIDs
     and GIDs to 0, which means that all users will appear to be root!

   Compatibility of NIS override evaluation
     When Sun originally added NIS support to their getpwent(3) routines, they
     took into account the fact that the SunOS password /etc/passwd file is in
     plain ASCII format. The SunOS documentation claims that adding a '+'
     entry to the password file causes the contents of the NIS password
     database to be 'inserted' at the position in the file where the '+' entry
     appears. If, for example, the administrator places the +:::::: entry in
     the middle of /etc/passwd, then the entire contents of the NIS password
     map would appear as though it had been copied into the middle of the
     password file. If the administrator places the +:::::: entry at both the
     middle and the end of /etc/passwd, then the NIS password map would appear
     twice: once in the middle of the file and once at the end. (By using
     override entries instead of simple wildcards, other combinations could be

     By contrast, FreeBSD does not have a single ASCII password file: it has a
     hashed password database. This database does not have an easily-defined
     beginning, middle or end, which makes it very hard to design a scheme
     that is 100% compatible with SunOS.  For example, the getpwnam() and
     getpwuid() functions in FreeBSD are designed to do direct queries to the
     hash database rather than a linear search. This approach is faster on
     systems where the password database is large. However, when using direct
     database queries, the system does not know or care about the order of the
     original password file, and therefore it cannot easily apply the same
     override logic used by SunOS.

     Instead, FreeBSD groups all the NIS override entries together and
     constructs a filter out of them. Each NIS password entry is compared
     against the override filter exactly once and treated accordingly: if the
     filter allows the entry through unaltered, it's treated unaltered; if the
     filter calls for remapping of fields, then fields are remapped; if the
     filter calls for explicit exclusion (i.e. the entry matches a '-'
     override), the entry is ignored; if the entry doesn't match against any
     of the filter specifications, it's discarded.

     Again, note that the NIS '+' and '-' entries themselves are handled in
     the order in which they were specified in the /etc/master.passwd file
     since doing otherwise would lead to unpredictable behavior.

     The end result is that FreeBSD's provides a very close approximation of
     SunOS's behavior while maintaining the database paradigm, though the
     getpwent(3) functions do behave somewhat differently from their SunOS
     counterparts.  The primary differences are:

           +o   Each NIS password map record can be mapped into the password
               local password space only once.

           +o   The placement of the NIS '+' and '-' entries does not
               necessarily affect where NIS password records will be mapped
               into the password space.

     In %99 of all FreeBSD configurations, NIS client behavior will be
     indistinguishable from that of SunOS or other similar systems. Even so,
     users should be aware of these architectural differences.

   Using groups instead of netgroups for NIS overrides
     FreeBSD offers the capability to do override matching based on user
     groups rather than netgroups. If, for example, an NIS entry is specified


     the system will first try to match users against a netgroup called
     `operator'. If an `operator' netgroup doesn't exist, the system will try
     to match users against the normal `operator' group instead.

   Changes in behavior from older versions of
     FreeBSD There have been several bug fixes and improvements in FreeBSD's
     NIS/YP handling, some of which have caused changes in behavior.  While
     the behavior changes are generally positive, it is important that users
     and system administrators be aware of them:

           1.   In versions prior to 2.0.5, reverse lookups (i.e. using
                getpwuid()) would not have overrides applied, which is to say
                that it was possible for getpwuid() to return a login name
                that getpwnam() would not recognize. This has been fixed:
                overrides specified in /etc/master.passwd now apply to all
                getpwent(3) functions.

           2.   Prior to FreeBSD 2.0.5, netgroup overrides did not work at
                all, largely because FreeBSD did not have support for reading
                netgroups through NIS. Again, this has been fixed, and
                netgroups can be specified just as in SunOS and similar NIS-
                capable systems.

           3.   FreeBSD now has NIS server capabilities and supports the use
                of master.passwd NIS maps in addition to the standard Sixth
                Edition format passwd maps.  This means that you can specify
                change, expiration and class information through NIS, provided
                you use a FreeBSD system as the NIS server.

     /etc/passwd         ASCII password file, with passwords removed
     /etc/pwd.db         db(3) -format password database, with passwords
     /etc/master.passwd  ASCII password file, with passwords intact
     /etc/spwd.db        db(3) -format password database, with passwords

     chpass(1), login(1), passwd(1), getpwent(3), login.conf(5),
     login_getclass(3), yp(4), login.conf(5), adduser(8), pwd_mkdb(8),
     vipw(8), pw(8)

     User information should (and eventually will) be stored elsewhere.

     The YP/NIS password database makes encrypted passwords visible to
     ordinary users, thus making password cracking easier unless you use
     shadow passwords with the master.passwd maps and FreeBSD's ypserv(8)

     Unless you're using FreeBSD's ypserv(8), which supports the use of
     master.passwd type maps, the YP/NIS password database will be in old-
     style (Sixth Edition) format, which means that site-wide values for user
     login class, password expiration date, and other fields present in the
     current format will not be available when a FreeBSD system is used as a
     client with a standard NIS server.

     The password file format has changed since 4.3BSD.  The following awk
     script can be used to convert your old-style password file into a new
     style password file.  The additional fields ``class'', ``change'' and
     ``expire'' are added, but are turned off by default.  These fields can
     then be set using vipw(8) or pw(8).

           BEGIN { FS = ":"}
           { print $1 ":" $2 ":" $3 ":" $4 "::0:0:" $5 ":" $6 ":" $7 }

     A passwd file format appeared in Version 6 AT&T UNIX.  The YP/NIS
     functionality is modeled after SunOS and first appeared in FreeBSD 1.1
     The override capability is new in FreeBSD 2.0.  The override capability
     was updated to properly support netgroups in FreeBSD 2.0.5.  Support for
     comments first appeared in FreeBSD 3.0.

FreeBSD 11.0-PRERELEASE       September 29, 1994       FreeBSD 11.0-PRERELEASE


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