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1 .\" Copyright (c) 1993 Michael Haardt (michael@moria.de),
2 .\" Fri Apr 2 11:32:09 MET DST 1993
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25 .\" Modified Sun Jul 25 10:46:28 1993 by Rik Faith (faith@cs.unc.edu)
26 .\" Modified Sun Aug 21 18:12:27 1994 by Rik Faith (faith@cs.unc.edu)
27 .\" Modified Sun Jun 18 01:53:57 1995 by Andries Brouwer (aeb@cwi.nl)
28 .\" Modified Mon Jan 5 20:24:40 MET 1998 by Michael Haardt
29 .\" (michael@cantor.informatik.rwth-aachen.de)
30 .TH PASSWD 5 2018-04-30 "Linux" "Linux Programmer's Manual"
31 .SH NAME
32 passwd \- password file
33 .SH DESCRIPTION
34 The
35 .IR /etc/passwd
36 file is a text file that describes user login accounts for the system.
37 It should have read permission allowed for all users (many utilities, like
38 .BR ls (1)
39 use it to map user IDs to usernames), 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 an \(aqx\(aq character in the password field,
50 and the encrypted passwords are in
51 .IR /etc/shadow ,
52 which is readable by the superuser only.
53 .PP
54 If the encrypted password, whether in
55 .I /etc/passwd
56 or in
57 .IR /etc/shadow ,
58 is an empty string, login is allowed without even asking for a password.
59 Note that this functionality may be intentionally disabled in applications,
60 or configurable (for example using the "nullok" or "nonull" arguments to
61 pam_unix.so).
62 .PP
63 If the encrypted password in
64 .I /etc/passwd
65 is "\fI*NP*\fP" (without the quotes),
66 the shadow record should be obtained from an NIS+ server.
67 .PP
68 Regardless of whether shadow passwords are used, many system administrators
69 use an asterisk (*) in the encrypted password field to make sure
70 that this user can not authenticate themself using a
71 password.
72 (But see NOTES below.)
73 .PP
74 If you create a new login, first put an asterisk (*) in the password field,
75 then use
76 .BR passwd (1)
77 to set it.
78 .PP
79 Each line of the file describes a single user,
80 and contains seven colon-separated fields:
81 .PP
82 .in +4n
83 .EX
84 name:password:UID:GID:GECOS:directory:shell
85 .EE
86 .in
87 .PP
88 The field are as follows:
89 .TP 12
90 .I name
91 This is the user's login name.
92 It should not contain capital letters.
93 .TP
94 .I password
95 This is either the encrypted user password,
96 an asterisk (*), or the letter \(aqx\(aq.
97 (See
98 .BR pwconv (8)
99 for an explanation of \(aqx\(aq.)
100 .TP
101 .I UID
102 The privileged
103 .I root
104 login account (superuser) has the user ID 0.
105 .TP
106 .I GID
107 This is the numeric primary group ID for this user.
108 (Additional groups for the user are defined in the system group file; see
109 .BR group (5)).
110 .TP
111 .I GECOS
112 This field (sometimes called the "comment field")
113 is optional and used only for informational purposes.
114 Usually, it contains the full username.
115 Some programs (for example,
116 .BR finger (1))
117 display information from this field.
118 .IP
119 GECOS stands for "General Electric Comprehensive Operating System",
120 which was renamed to GCOS when
121 GE's large systems division was sold to Honeywell.
122 Dennis Ritchie has reported: "Sometimes we sent printer output or
123 batch jobs to the GCOS machine.
124 The gcos field in the password file was a place to stash the
125 information for the $IDENTcard.
126 Not elegant."
127 .TP
128 .I directory
129 This is the user's home directory:
130 the initial directory where the user is placed after logging in.
131 The value in this field is used to set the
132 .B HOME
133 environment variable.
134 .TP
135 .I shell
136 This is the program to run at login (if empty, use
137 .IR /bin/sh ).
138 If set to a nonexistent executable, the user will be unable to login
139 through
140 .BR login (1).
141 The value in this field is used to set the
142 .B SHELL
143 environment variable.
144 .SH FILES
145 .I /etc/passwd
146 .SH NOTES
147 If you want to create user groups, there must be an entry in
148 .IR /etc/group ,
149 or no group will exist.
150 .PP
151 If the encrypted password is set to an asterisk (*), the user will be unable
152 to login using
153 .BR login (1),
154 but may still login using
155 .BR rlogin (1),
156 run existing processes and initiate new ones through
157 .BR rsh (1),
158 .BR cron (8),
159 .BR at (1),
160 or mail filters, etc.
161 Trying to lock an account by simply changing the
162 shell field yields the same result and additionally allows the use of
163 .BR su (1).
164 .SH SEE ALSO
165 .BR chfn (1),
166 .BR chsh (1),
167 .BR login (1),
168 .BR passwd (1),
169 .BR su (1),
170 .BR crypt (3),
171 .BR getpwent (3),
172 .BR getpwnam (3),
173 .BR group (5),
174 .BR shadow (5),
175 .BR vipw (8)