Man Pages

passwd(5) - phpMan passwd(5) - phpMan

Command: man perldoc info search(apropos)  

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

       passwd - password file

       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  pass-
       words  for each account.  It should have general read permission (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 "x" instead of encrypted passwords, 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 with-
       out 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

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

       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, then use passwd(1) to set it.

       There is one entry per line, and each line has the format:


       The field descriptions are:

              account   the name of the user on the system.  It should not contain capital letters.

              password  the encrypted user password, an asterisk (*), or the letter 'x'.  (See pwconv(8) for an expla-
                        nation of 'x'.)

              UID       the numerical user ID.

              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  username.   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).


       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 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  addi-
       tionally allows the use of su(1).

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

       This  page  is part of release 3.22 of the Linux man-pages project.  A description of the project, and informa-
       tion about reporting bugs, can be found at

Linux                             1998-01-05                         PASSWD(5)