NAME | DESCRIPTION | FILES | NOTES | SEE ALSO | COLOPHON

PASSWD(5)                 Linux Programmer's Manual                PASSWD(5)

NAME         top

       passwd - password file

DESCRIPTION         top

       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 an 'x' character in the
       password field, 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 applications, 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 an NIS+ server.

       Regardless of whether shadow passwords are used, many system
       administrators 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 contains seven
       colon-separated fields:

              name:password:UID:GID:GECOS:directory:shell

       The field are as follows:

       name        This is the user's login name.  It should not contain
                   capital letters.

       password    This is either the encrypted user password, an asterisk
                   (*), or the letter 'x'.  (See pwconv(8) for an
                   explanation of 'x'.)

       UID         The privileged root login account (superuser) has the
                   user ID 0.

       GID         This is the numeric primary group ID for this user.
                   (Additional groups for the user are defined in the system
                   group file; see group(5)).

       GECOS       This field (sometimes called the "comment field") is
                   optional and used only for informational purposes.
                   Usually, it contains the full username.  Some programs
                   (for example, finger(1)) display information from this
                   field.

                   GECOS stands for "General Electric Comprehensive
                   Operating System", 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   This is the user's home directory: the initial directory
                   where the user is placed after logging in.  The value in
                   this field is used to set the HOME environment variable.

       shell       This is 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).  The value in
                   this field is used to set the SHELL environment variable.

FILES         top

       /etc/passwd

NOTES         top

       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 ALSO         top

       login(1), passwd(1), su(1), crypt(3), getpwent(3), getpwnam(3),
       group(5), shadow(5)

COLOPHON         top

       This page is part of release 3.71 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at
       http://www.kernel.org/doc/man-pages/.

Linux                            2014-02-11                        PASSWD(5)