1passwd(5) File Formats Manual passwd(5)
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6 passwd - password file
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9 The /etc/passwd file is a text file that describes user login accounts
10 for the system. It should have read permission allowed for all users
11 (many utilities, like ls(1) use it to map user IDs to usernames), but
12 write access only for the superuser.
13 In the good old days there was no great problem with this general read
15 permission. Everybody could read the encrypted passwords, but the
16 hardware was too slow to crack a well-chosen password, and moreover the
17 basic assumption used to be that of a friendly user-community. These
18 days many people run some version of the shadow password suite, where
19 /etc/passwd has an 'x' character in the password field, and the en‐
20 crypted passwords are in /etc/shadow, which is readable by the supe‐
21 ruser only.
22 If the encrypted password, whether in /etc/passwd or in /etc/shadow, is
24 an empty string, login is allowed without even asking for a password.
25 Note that this functionality may be intentionally disabled in applica‐
26 tions, or configurable (for example using the "nullok" or "nonull" ar‐
27 guments to pam_unix(8)).
28 If the encrypted password in /etc/passwd is "*NP*" (without the
30 quotes), the shadow record should be obtained from an NIS+ server.
31 Regardless of whether shadow passwords are used, many system adminis‐
33 trators use an asterisk (*) in the encrypted password field to make
34 sure that this user can not authenticate themself using a password.
35 (But see NOTES below.)
36 If you create a new login, first put an asterisk (*) in the password
38 field, then use passwd(1) to set it.
39 Each line of the file describes a single user, and contains seven
41 colon-separated fields:
42 name:password:UID:GID:GECOS:directory:shell
44 The field are as follows:
46 name This is the user's login name. It should not contain capi‐
48 tal letters.
49 password This is either the encrypted user password, an asterisk
51 (*), or the letter 'x'. (See pwconv(8) for an explanation
52 of 'x'.)
53 UID The privileged root login account (superuser) has the user
55 ID 0.
56 GID This is the numeric primary group ID for this user. (Addi‐
58 tional groups for the user are defined in the system group
59 file; see group(5)).
60 GECOS This field (sometimes called the "comment field") is op‐
62 tional and used only for informational purposes. Usually,
63 it contains the full username. Some programs (for example,
64 finger(1)) display information from this field.
65 GECOS stands for "General Electric Comprehensive Operating
67 System", which was renamed to GCOS when GE's large systems
68 division was sold to Honeywell. Dennis Ritchie has re‐
69 ported: "Sometimes we sent printer output or batch jobs to
70 the GCOS machine. The gcos field in the password file was
71 a place to stash the information for the $IDENTcard. Not
72 elegant."
73 directory This is the user's home directory: the initial directory
75 where the user is placed after logging in. The value in
76 this field is used to set the HOME environment variable.
77 shell This is the program to run at login (if empty, use
79 /bin/sh). If set to a nonexistent executable, the user
80 will be unable to login through login(1). The value in
81 this field is used to set the SHELL environment variable.
82
84 /etc/passwd
85
87 If you want to create user groups, there must be an entry in
88 /etc/group, or no group will exist.
89 If the encrypted password is set to an asterisk (*), the user will be
91 unable to login using login(1), but may still login using rlogin(1),
92 run existing processes and initiate new ones through rsh(1), cron(8),
93 at(1), or mail filters, etc. Trying to lock an account by simply
94 changing the shell field yields the same result and additionally allows
95 the use of su(1).
96
98 chfn(1), chsh(1), login(1), passwd(1), su(1), crypt(3), getpwent(3),
99 getpwnam(3), group(5), shadow(5), vipw(8)
100Linux man-pages 6.05 2023-02-05 passwd(5)