PASSWD(5) Linux Programmer's Manual PASSWD(5)NAMEpasswd - password file
DESCRIPTION
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. Everybody 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-community. These
days many people run some version of the shadow password suite, where
/etc/passwd has "x" instead of encrypted passwords, 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 applica‐
tions, 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 a NIS+ server.
Regardless of whether shadow passwords are used, many system adminis‐
trators use an asterisk 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 has the following
format:
account:password:UID:GID:GECOS:directory:shell
The field are as follows:
account the name of the user on the system. It should not contain
capital letters.
password the encrypted user password, an asterisk (*), or the letter
'x'. (See pwconv(8) for an explanation of 'x'.)
UID the numeric user ID.
GID the numeric primary group ID for this user.
GECOS This field is optional and used only for informational pur‐
poses. Usually, it contains the full username. GECOS
stands for "General Electric Comprehensive Operating Sys‐
tem", which was renamed to GCOS when GE's large systems
division was sold to Honeywell. Dennis 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 the user's $HOME directory.
shell 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).
FILES
/etc/passwd
NOTES
If you want to create user groups, there must be an entry in
/etc/group, or no group will exist.
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 of su(1).
SEE ALSOlogin(1), passwd(1), su(1), getpwent(3), getpwnam(3), group(5),
shadow(5)COLOPHON
This page is part of release 3.35 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can
be found at http://man7.org/linux/man-pages/.
Linux 2010-10-21 PASSWD(5)
