PASSWD(5) Linux Programmer's Manual PASSWD(5)
passwd - password file
The /etc/passwd file is a text file that describes user login accounts for the system. It
should have read permission allowed for all users (many utilities, like ls(1) use it to
map user IDs to usernames), but write access only for the superuser.
In the good old days there was no great problem with this general read permission. Every-
body could read the encrypted passwords, but the hardware was too slow to crack a well-
chosen password, and moreover the basic assumption used to be that of a friendly user-com-
munity. These days many people run some version of the shadow password suite, where
/etc/passwd has an 'x' character in the password field, and the encrypted passwords are in
/etc/shadow, which is readable by the superuser only.
If the encrypted password, whether in /etc/passwd or in /etc/shadow, is an empty string,
login is allowed without even asking for a password. Note that this functionality may be
intentionally disabled in applications, or configurable (for example using the "nullok" or
"nonull" arguments to pam_unix.so).
If the encrypted password in /etc/passwd is "*NP*" (without the quotes), the shadow record
should be obtained from an NIS+ server.
Regardless of whether shadow passwords are used, many system administrators use an aster-
isk (*) in the encrypted password field to make sure that this user can not authenticate
him- or herself using a password. (But see NOTES below.)
If you create a new login, first put an asterisk (*) in the password field, then use
passwd(1) to set it.
Each line of the file describes a single user, and contains seven colon-separated fields:
The field are as follows:
name This is the user's login name. It should not contain capital letters.
password This is either the encrypted user password, an asterisk (*), or the letter
'x'. (See pwconv(8) for an explanation of 'x'.)
UID The privileged root login account (superuser) has the user ID 0.
GID This is the numeric primary group ID for this user. (Additional groups for
the user are defined in the system group file; see group(5)).
GECOS This field (sometimes called the "comment field") is optional and used only
for informational purposes. Usually, it contains the full username. Some
programs (for example, finger(1)) display information from this field.
GECOS stands for "General Electric Comprehensive Operating System", which was
renamed to GCOS when GE's large systems division was sold to Honeywell. Den-
nis Ritchie has reported: "Sometimes we sent printer output or batch jobs to
the GCOS machine. The gcos field in the password file was a place to stash
the information for the $IDENTcard. Not elegant."
directory This is the user's home directory: the initial directory where the user is
placed after logging in. The value in this field is used to set the HOME
shell This is the program to run at login (if empty, use /bin/sh). If set to a
nonexistent executable, the user will be unable to login through login(1).
The value in this field is used to set the SHELL environment variable.
If you want to create user groups, there must be an entry in /etc/group, or no group will
If the encrypted password is set to an asterisk (*), the user will be unable to login
using login(1), but may still login using rlogin(1), run existing processes and initiate
new ones through rsh(1), cron(8), at(1), or mail filters, etc. Trying to lock an account
by simply changing the shell field yields the same result and additionally allows the use
login(1), passwd(1), su(1), getpwent(3), getpwnam(3), crypt(3), group(5), shadow(5)
This page is part of release 3.55 of the Linux man-pages project. A description of the
project, and information about reporting bugs, can be found at
Linux 2012-05-03 PASSWD(5)