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 or 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.
The group field is the group that the user will be placed in upon login. Since this system supports multiple groups (see groups(1)) this field currently has little special meaning.
The class field is currently unused. In the near future it will be a key to a termcap(5) style database of user attributes.
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 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 to turn off the account aging feature.
The gecos field normally contains comma (``,'') separated subfields as follows:
name user's full name office user's office number wphone user's work phone number hphone user's home phone number
This information is used by the finger(1) program.
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.
Lines beginning with a ``-'' (minus sign) are entries marked as being excluded from any following inclusions, which are marked with a ``+'' (plus sign).
If the second character of the line is a ``@'' (at sign), the operation involves the user fields of all entries in the netgroup specified by the remaining characters of the name field. Otherwise, the remainder of the name field is assumed to be a specific user name.
The ``+'' token may also be alone in the name field, which causes all users from the passwd.byname and passwd.byuid YP maps to be included.
If the entry contains non-empty uid or gid fields, the specified numbers will override the information retrieved from the YP maps. As well, if the gecos, dir or shell entries contain text, it will override the information included via YP. On some systems, the passwd field may also be overriden.
"Managing NFS and NIS" (O'Reilly & Associates)
Placing YP exclusions in the file after any inclusions will have unexpected results.
BEGIN { FS = ":"}
{ print $1 ":" $2 ":" $3 ":" $4 "::0:0:" $5 ":" $6 ":" $7 }
YP file format first appeared in SunOS.