man5/passwd.5

   1 .\" Copyright (c) 1993 Michael Haardt (michael@moria.de), Fri Apr  2 11:32:09 MET DST 1993
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  23 .\" Modified Sun Jul 25 10:46:28 1993 by Rik Faith (faith@cs.unc.edu)
  24 .\" Modified Sun Aug 21 18:12:27 1994 by Rik Faith (faith@cs.unc.edu)
  25 .\" Modified Sun Jun 18 01:53:57 1995 by Andries Brouwer (aeb@cwi.nl)
  26 .\" Modified Mon Jan  5 20:24:40 MET 1998 by Michael Haardt
  27 .\"  (michael@cantor.informatik.rwth-aachen.de)
  28 .TH PASSWD 5 1998-01-05 "Linux" "Linux Programmer's Manual"
  29 .SH NAME
  30 passwd \- password file
  31 .SH DESCRIPTION
  32 .B Passwd
  33 is a text file, that contains a list of the system's accounts,
  34 giving for each account some useful information like user ID,
  35 group ID, home directory, shell, etc.
  36 Often, it also contains the encrypted passwords for each account.
  37 It should have general read permission (many utilities, like
  38 .BR ls (1)
  39 use it to map user IDs to user names), but write access only for the
  40 superuser.
  41 .PP
  42 In the good old days there was no great problem with this general
  43 read permission.
  44 Everybody could read the encrypted passwords, but the
  45 hardware was too slow to crack a well-chosen password, and moreover, the
  46 basic assumption used to be that of a friendly user-community.
  47 These days many people run some version of the shadow password suite, where
  48 .I /etc/passwd
  49 has asterisks (*) instead of encrypted passwords,
  50 and the encrypted passwords are in
  51 .I /etc/shadow
  52 which is readable by the superuser only.
  53 .PP
  54 Regardless of whether shadow passwords are used, many sysadmins
  55 use an asterisk in the encrypted password field to make sure
  56 that this user can not authenticate him- or herself using a
  57 password. (But see the Notes below.)
  58 .PP
  59 If you create a new login, first put an asterisk in the password field,
  60 then use
  61 .BR passwd (1)
  62 to set it.
  63 .PP
  64 There is one entry per line, and each line has the format:
  65 .sp
  66 .RS
  67 account:password:UID:GID:GECOS:directory:shell
  68 .RE
  69 .sp
  70 The field descriptions are:
  71 .RS
  72 .TP 1.0in
  73 .I account
  74 the name of the user on the system.
  75 It should not contain capital letters.
  76 .TP
  77 .I password
  78 the encrypted user password, an asterisk (*), or the letter 'x'.
  79 (See
  80 .BR pwconv (8)
  81 for an explanation of 'x'.)
  82 .TP
  83 .I UID
  84 the numerical user ID.
  85 .TP
  86 .I GID
  87 the numerical primary group ID for this user.
  88 .TP
  89 .I GECOS
  90 This field is optional and only used for informational purposes.
  91 Usually, it contains the full user name.
  92 GECOS means General Electric
  93 Comprehensive Operating System, which has been renamed to GCOS when
  94 GE's large systems division was sold to Honeywell.
  95 Dennis Ritchie has reported: "Sometimes we sent printer output or
  96 batch jobs to the GCOS machine.
  97 The gcos field in the password file was a place to stash the
  98 information for the $IDENTcard.
  99 Not elegant."
 100 .TP
 101 .I directory
 102 the user's $HOME directory.
 103 .TP
 104 .I shell
 105 the program to run at login (if empty, use
 106 .IR /bin/sh ).
 107 If set to a non-existing executable, the user will be unable to login
 108 through
 109 .BR login (1).
 110 .RE
 111 .SH FILES
 112 .I /etc/passwd
 113 .SH NOTES
 114 If you want to create
 115 user groups, their GIDs must be equal and there must be an entry in
 116 \fI/etc/group\fP, or no group will exist.
 117 .PP
 118 If the encrypted password is set to an asterisk, the user will be unable
 119 to login using
 120 .BR login (1),
 121 but may still login using
 122 .BR rlogin (1),
 123 run existing processes and initiate new ones through
 124 .BR rsh (1),
 125 .BR cron (8),
 126 .BR at (1),
 127 or mail filters, etc.
 128 Trying to lock an account by simply changing the
 129 shell field yields the same result and additionally allows the use of
 130 .BR su (1).
 131 .SH "SEE ALSO"
 132 .BR login (1),
 133 .BR passwd (1),
 134 .BR su (1),
 135 .BR group (5),
 136 .BR shadow (5)