1PASSWD(5) Linux Programmer's Manual PASSWD(5)
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6 passwd - password file
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9 Passwd is a text file, that contains a list of the system's accounts,
10 giving for each account some useful information like user ID, group ID,
11 home directory, shell, etc. Often, it also contains the encrypted
12 passwords for each account. It should have general read permission
13 (many utilities, like ls(1) use it to map user IDs to usernames), but
14 write access only for the superuser.
15 In the good old days there was no great problem with this general read
17 permission. Everybody could read the encrypted passwords, but the
18 hardware was too slow to crack a well-chosen password, and moreover,
19 the basic assumption used to be that of a friendly user-community.
20 These days many people run some version of the shadow password suite,
21 where /etc/passwd has "x" instead of encrypted passwords, and the
22 encrypted passwords are in /etc/shadow which is readable by the supe‐
23 ruser only.
24 If the encrypted password, whether in /etc/passwd or in /etc/shadow, is
26 an empty string, login is allowed without even asking for a password.
27 Note that this functionality may be intentionally disabled in applica‐
28 tions, or configurable (for example using the "nullok" or "nonull"
29 arguments to pam_unix.so).
30 If the encrypted password in /etc/passwd is "*NP*" (without the
32 quotes), the shadow record should be obtained from a NIS+ server.
33 Regardless of whether shadow passwords are used, many sysadmins use an
35 asterisk in the encrypted password field to make sure that this user
36 can not authenticate him- or herself using a password. (But see the
37 Notes below.)
38 If you create a new login, first put an asterisk in the password field,
40 then use passwd(1) to set it.
41 There is one entry per line, and each line has the format:
43 account:password:UID:GID:GECOS:directory:shell
45 The field descriptions are:
47 account the name of the user on the system. It should not
49 contain capital letters.
50 password the encrypted user password, an asterisk (*), or the
52 letter 'x'. (See pwconv(8) for an explanation of
53 'x'.)
54 UID the numerical user ID.
56 GID the numerical primary group ID for this user.
58 GECOS This field is optional and only used for informational
60 purposes. Usually, it contains the full username.
61 GECOS means General Electric Comprehensive Operating
62 System, which has been renamed to GCOS when GE's large
63 systems division was sold to Honeywell. Dennis
64 Ritchie has reported: "Sometimes we sent printer out‐
65 put or batch jobs to the GCOS machine. The gcos field
66 in the password file was a place to stash the informa‐
67 tion for the $IDENTcard. Not elegant."
68 directory the user's $HOME directory.
70 shell the program to run at login (if empty, use /bin/sh).
72 If set to a non-existing executable, the user will be
73 unable to login through login(1).
74
76 /etc/passwd
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79 If you want to create user groups, their GIDs must be equal and there
80 must be an entry in /etc/group, or no group will exist.
81 If the encrypted password is set to an asterisk, the user will be
83 unable to login using login(1), but may still login using rlogin(1),
84 run existing processes and initiate new ones through rsh(1), cron(8),
85 at(1), or mail filters, etc. Trying to lock an account by simply
86 changing the shell field yields the same result and additionally allows
87 the use of su(1).
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90 login(1), passwd(1), su(1), getpwent(3), getpwnam(3), group(5),
91 shadow(5)
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94 This page is part of release 3.22 of the Linux man-pages project. A
95 description of the project, and information about reporting bugs, can
96 be found at http://www.kernel.org/doc/man-pages/.
97Linux 1998-01-05 PASSWD(5)