1SHADOW(5) File Formats and Conversions SHADOW(5)
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6 shadow - shadowed password file
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9 shadow is a file which contains the password information for the
10 system's accounts and optional aging information.
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12 This file must not be readable by regular users if password security is
13 to be maintained.
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15 Each line of this file contains 9 fields, separated by colons (“:”), in
16 the following order:
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18 login name
19 It must be a valid account name, which exist on the system.
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21 encrypted password
22 This field may be empty, in which case no passwords are required to
23 authenticate as the specified login name. However, some
24 applications which read the /etc/shadow file may decide not to
25 permit any access at all if the password field is empty.
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27 A password field which starts with an exclamation mark means that
28 the password is locked. The remaining characters on the line
29 represent the password field before the password was locked.
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31 Refer to crypt(3) for details on how this string is interpreted.
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33 If the password field contains some string that is not a valid
34 result of crypt(3), for instance ! or *, the user will not be able
35 to use a unix password to log in (but the user may log in the
36 system by other means).
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38 date of last password change
39 The date of the last password change, expressed as the number of
40 days since Jan 1, 1970 00:00 UTC.
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42 The value 0 has a special meaning, which is that the user should
43 change her password the next time she will log in the system.
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45 An empty field means that password aging features are disabled.
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47 minimum password age
48 The minimum password age is the number of days the user will have
49 to wait before she will be allowed to change her password again.
50
51 An empty field and value 0 mean that there is no minimum password
52 age.
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54 maximum password age
55 The maximum password age is the number of days after which the user
56 will have to change her password.
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58 After this number of days is elapsed, the password may still be
59 valid. The user should be asked to change her password the next
60 time she will log in.
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62 An empty field means that there are no maximum password age, no
63 password warning period, and no password inactivity period (see
64 below).
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66 If the maximum password age is lower than the minimum password age,
67 the user cannot change her password.
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69 password warning period
70 The number of days before a password is going to expire (see the
71 maximum password age above) during which the user should be warned.
72
73 An empty field and value 0 mean that there are no password warning
74 period.
75
76 password inactivity period
77 The number of days after a password has expired (see the maximum
78 password age above) during which the password should still be
79 accepted (and the user should update her password during the next
80 login).
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82 After expiration of the password and this expiration period is
83 elapsed, no login is possible for the user. The user should contact
84 her administrator.
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86 An empty field means that there are no enforcement of an inactivity
87 period.
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89 account expiration date
90 The date of expiration of the account, expressed as the number of
91 days since Jan 1, 1970 00:00 UTC.
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93 Note that an account expiration differs from a password expiration.
94 In case of an account expiration, the user shall not be allowed to
95 login. In case of a password expiration, the user is not allowed to
96 login using her password.
97
98 An empty field means that the account will never expire.
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100 The value 0 should not be used as it is interpreted as either an
101 account with no expiration, or as an expiration on Jan 1, 1970.
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103 reserved field
104 This field is reserved for future use.
105
107 /etc/passwd
108 User account information.
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110 /etc/shadow
111 Secure user account information.
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113 /etc/shadow-
114 Backup file for /etc/shadow.
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116 Note that this file is used by the tools of the shadow toolsuite,
117 but not by all user and password management tools.
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120 chage(1), login(1), passwd(1), passwd(5), pwck(8), pwconv(8),
121 pwunconv(8), su(1), sulogin(8).
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125shadow-utils 4.9 11/19/2021 SHADOW(5)