PASSWD(5) BSD File Formats Manual PASSWD(5)
passwd, master.passwd -- format of the password file
The master.passwd file, readable only by root, consists of newline-sepa-
rated 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 login user ID.
gid User's login group ID.
class User's general classification (see login.conf(5)).
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.
The publicly-readable passwd file is generated from the master.passwd
file by pwd_mkdb(8) and has the class, change, and expire fields removed.
Also, the encrypted password field is replaced by an asterisk.
The password files should never be edited by hand; vipw(8) should be used
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 con-
trol file access.
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.
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 ('-'); also, it is strongly suggested that nei-
ther uppercase 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. By convention,
accounts that are not intended to be logged in to (e.g. bin, daemon,
sshd) only contain a single asterisk in the password field. Note that
there is nothing special about '*', it is just one of many characters
that cannot occur in a valid encrypted password (see crypt(3)). Simi-
larly, login accounts not allowing password authentication but allowing
other authentication methods, for example public key authentication, con-
ventionally have 13 asterisks in the password field. Because
master.passwd contains the encrypted user passwords, it should not be
readable by anyone without appropriate privileges.
Configuration for the cipher used to encrypt the password information is
contained in login.conf(5).
The group field is the primary group that the user will be placed in upon
login. Note that the group(5) file may grant the user access to supple-
The class field is used by login(1) and other programs to determine which
entry in the login.conf(5) database should be used.
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
The gecos field normally contains comma separated subfields as follows:
name User's full name.
office User's office location.
wphone User's work phone number.
hphone User's home phone number.
The full name may contain an ampersand ('&'), which will be replaced by
the capitalized login name when the gecos field is displayed or used by
various programs such as finger(1), sendmail(8), etc.
The office and phone number subfields, if they exist, are used by the
finger(1) program and possibly by other applications.
The 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 group.
The shell field is the command interpreter the user prefers. If there is
nothing in the shell field, the default shell (/bin/sh) is assumed.
Accounts that are not intended to be logged in to usually have a shell of
If YP is active, the passwd file also supports standard YP exclusions and
inclusions, based on user names and netgroups.
Lines beginning with a '-' (minus sign) are entries marked as being
excluded from any following inclusions, which are marked with a '+' (plus
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. Additionally,
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 overridden. It is recommended that the standard way to enable YP
passwd support in /etc/master.passwd is:
which after pwd_mkdb(8) will result in /etc/passwd containing:
When YP is enabled but temporarily unavailable, login becomes impossible
for all users except those having an entry in the netid(5) file.
chpass(1), login(1), passwd(1), crypt(3), getpwent(3), login.conf(5),
netgroup(5), netid(5), adduser(8), Makefile.yp(8), pwd_mkdb(8), vipw(8),
Managing NFS and NIS (O'Reilly & Associates)
A passwd file format first appeared in Version 1 AT&T UNIX. The gecos
field first appeared in Version 3 AT&T UNIX; since the same version, the
passwords are encrypted. The gid field first appeared in Version 5 AT&T
UNIX; the class, change and expire fields as well as the master.passwd
file in 4.3BSD-Reno.
The YP file format first appeared in SunOS.
Placing YP exclusions in the file after any inclusions does not cancel
the earlier inclusions.
BSD April 25, 2017 BSD