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NAME

passwd, master.passwd — format of the password file

DESCRIPTION

The 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:

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 instead.

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 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 neither 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)). Similarly, login accounts not allowing password authentication but allowing other authentication methods, for example public key authentication, conventionally 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 supplementary groups.

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 aging feature.

The gecos field normally contains comma separated subfields as follows:

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 /sbin/nologin.

YP SUPPORT

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 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. 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:

+:*:0:0:::

When YP is enabled but temporarily unavailable, login becomes impossible for all users except those having an entry in the netid(5) file.

SEE ALSO

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), yp(8)

Managing NFS and NIS (O'Reilly & Associates)

HISTORY

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.

CAVEATS

Placing YP exclusions in the file after any inclusions does not cancel the earlier inclusions.