NAME
passwd - password file
DESCRIPTION
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 user names), 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 user name. 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).
NOTE
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(1),
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).
FILES
/etc/passwd
SEE ALSO
login(1),
passwd(1),
su(1),
group(5),
shadow(5)