Section: Linux Programmer's Manual (5)
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passwd - password file
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
use it to map user IDs to user names), but write access only for the
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
has asterisks (*) instead of encrypted passwords,
and the encrypted passwords are in
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,
to set it.
There is one entry per line, and each line has the format:
The field descriptions are:
the name of the user on the system. It should not contain capital letters.
the encrypted user password, an asterisk (*), or the letter 'x'.
for an explanation of 'x'.)
the numerical user ID.
the numerical primary group ID for this user.
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."
the user's $HOME directory.
the program to run at login (if empty, use
If set to a non-existing executable, the user will be unable to login
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
but may still login using
run existing processes and initiate new ones through
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
- SEE ALSO
linux.jgfs.net manual pages