NAME | DESCRIPTION | FILES | NOTES | SEE ALSO | COLOPHON
PASSWD(5) Linux Programmer's Manual PASSWD(5)
passwd - password file
Passwd is a text file, that contains a list of the system's accounts, giving
for each account some useful information like user ID, group ID, home
directory, shell, etc. Often, it also contains the encrypted passwords for
each account. It should have general read permission (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
asterisks (*) instead of encrypted passwords, and the encrypted passwords are
in /etc/shadow which is readable by the superuser only.
Regardless of whether shadow passwords are used, many sysadmins 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 the Notes below.)
If you create a new login, first put an asterisk in the password field, then
use passwd(1) to set it.
There is one entry per line, and each line has the format:
account:password:UID:GID:GECOS:directory:shell
The field descriptions are:
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 numerical user ID.
GID the numerical primary group ID for this user.
GECOS This field is optional and only used for informational
purposes. Usually, it contains the full username. GECOS
means General Electric Comprehensive Operating System, which
has been 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 non-existing executable, the user will be unable to
login through login(1).
/etc/passwd
If you want to create user groups, their GIDs must be equal and 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).
login(1), passwd(1), su(1), getpwent(3), getpwnam(3), group(5), shadow(5)
This page is part of release 3.23 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can be found
at http://www.kernel.org/doc/man-pages/.
Linux 1998-01-05 PASSWD(5)