Essential System Administration Pocket Reference

User Accounts

/etc/passwd

The password file

username:x:UID:GID:user-info:home-dir:login-shell

username	User account login name (generally limited to 8 characters).
x	Traditional password field, set to a fixed character (usually x) when a shadow password file is in use. AIX uses an exclamation point (!), and FreeBSD uses an asterisk (*).
UID	The user identification number.
GID	The user’s primary group membership.
user-info	Conventionally, contains the user’s full name and, possibly, other job-related information (e.g., office location or phone number). Up to five comma-separated subfields may be defined.
home-dir	The user’s home directory.
login-shell	The program used as the command interpreter for this user. On most systems, the /etc/shells file lists the full pathnames of valid shell programs; on AIX systems, valid shells are listed in the shells field in the usw stanza of /etc/security/login.cfg:         shells = /bin/sh, /bin/csh, ...

Shadow password files

/etc/shadow (Linux and Solaris)

user:pwd:changed:minlife:maxlife:warn:inactive:expires:

user	Username (as in /etc/passwd).
pwd	Encoded password.
changed	Last password change (Unix date format*).
minlife	Minimum number of days a user must keep a new password.
maxlife	Maximum password lifetime, in days.
warn	Days to warn in advance of an upcoming password expiration.
inactive	Days after password expiration that the account will be disabled.
expires	Date the account expires (Unix date format). ...