passwd(5) — Linux manual page


passwd(5)                  File Formats 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(8)).

       If the encrypted password in /etc/passwd is "*NP*" (without the
       quotes), the shadow record should be obtained from an NIS+

       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:


       The field are as follows:

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

              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

              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."

              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


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

       chfn(1), chsh(1), login(1), passwd(1), su(1), crypt(3),
       getpwent(3), getpwnam(3), group(5), shadow(5), vipw(8)

Linux man-pages (unreleased)     (date)                        passwd(5)

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