# passwd

## NAME



           passwd - password file
    


## DESCRIPTION



           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(8)).
    
           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 themself 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



           _/etc/passwd_
    


## NOTES



           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).
    


* * *