PASSWD (5)
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 *'s 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 a star 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 a star 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 or a star.
UID
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 a star, 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)
or
cron (1)
or
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
SEE ALSO
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