chpasswd(8)

1CHPASSWD(8)               System Management Commands               CHPASSWD(8)
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NAME

6       chpasswd - update passwords in batch mode
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SYNOPSIS

9       chpasswd [options]
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DESCRIPTION

12       The chpasswd command reads a list of user name and password pairs from
13       standard input and uses this information to update a group of existing
14       users. Each line is of the format:
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16       user_name:password
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18       By default the passwords must be supplied in clear-text, and are
19       encrypted by chpasswd. Also the password age will be updated, if
20       present.
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22       The default encryption algorithm can be defined for the system with the
23       ENCRYPT_METHOD or MD5_CRYPT_ENAB variables of /etc/login.defs, and can
24       be overwritten with the -e, -m, or -c options.
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26       chpasswd first updates all the passwords in memory, and then commits
27       all the changes to disk if no errors occurred for any user.
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29       This command is intended to be used in a large system environment where
30       many accounts are created at a single time.
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OPTIONS

33       The options which apply to the chpasswd command are:
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35       -c, --crypt-method METHOD
36           Use the specified method to encrypt the passwords.
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38           The available methods are DES, MD5, NONE, and SHA256 or SHA512 if
39           your libc support these methods.
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41           By default (if none of the -c, -m, or -e options are specified),
42           the encryption method is defined by the ENCRYPT_METHOD or
43           MD5_CRYPT_ENAB variables of /etc/login.defs.
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45       -e, --encrypted
46           Supplied passwords are in encrypted form.
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48       -h, --help
49           Display help message and exit.
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51       -m, --md5
52           Use MD5 encryption instead of DES when the supplied passwords are
53           not encrypted.
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55       -R, --root CHROOT_DIR
56           Apply changes in the CHROOT_DIR directory and use the configuration
57           files from the CHROOT_DIR directory. Only absolute paths are
58           supported.
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60       -s, --sha-rounds ROUNDS
61           Use the specified number of rounds to encrypt the passwords.
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63           The value 0 means that the system will choose the default number of
64           rounds for the crypt method (5000).
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66           A minimal value of 1000 and a maximal value of 999,999,999 will be
67           enforced.
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69           You can only use this option with the SHA256 or SHA512 crypt
70           method.
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72           By default, the number of rounds is defined by the
73           SHA_CRYPT_MIN_ROUNDS and SHA_CRYPT_MAX_ROUNDS variables in
74           /etc/login.defs.
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CAVEATS

77       Remember to set permissions or umask to prevent readability of
78       unencrypted files by other users.
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CONFIGURATION

81       The following configuration variables in /etc/login.defs change the
82       behavior of this tool:
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84       ENCRYPT_METHOD (string)
85           This defines the system default encryption algorithm for encrypting
86           passwords (if no algorithm are specified on the command line).
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88           It can take one of these values: DES (default), MD5, SHA256,
89           SHA512. MD5 and DES should not be used for new hashes, see crypt(5)
90           for recommendations.
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92           Note: this parameter overrides the MD5_CRYPT_ENAB variable.
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94       MD5_CRYPT_ENAB (boolean)
95           Indicate if passwords must be encrypted using the MD5-based
96           algorithm. If set to yes, new passwords will be encrypted using the
97           MD5-based algorithm compatible with the one used by recent releases
98           of FreeBSD. It supports passwords of unlimited length and longer
99           salt strings. Set to no if you need to copy encrypted passwords to
100           other systems which don't understand the new algorithm. Default is
101           no.
102
103           This variable is superseded by the ENCRYPT_METHOD variable or by
104           any command line option used to configure the encryption algorithm.
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106           This variable is deprecated. You should use ENCRYPT_METHOD.
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108       SHA_CRYPT_MIN_ROUNDS (number), SHA_CRYPT_MAX_ROUNDS (number)
109           When ENCRYPT_METHOD is set to SHA256 or SHA512, this defines the
110           number of SHA rounds used by the encryption algorithm by default
111           (when the number of rounds is not specified on the command line).
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113           With a lot of rounds, it is more difficult to brute forcing the
114           password. But note also that more CPU resources will be needed to
115           authenticate users.
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117           If not specified, the libc will choose the default number of rounds
118           (5000), which is orders of magnitude too low for modern hardware.
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120           The values must be inside the 1000-999,999,999 range.
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122           If only one of the SHA_CRYPT_MIN_ROUNDS or SHA_CRYPT_MAX_ROUNDS
123           values is set, then this value will be used.
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125           If SHA_CRYPT_MIN_ROUNDS > SHA_CRYPT_MAX_ROUNDS, the highest value
126           will be used.
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FILES

129       /etc/passwd
130           User account information.
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132       /etc/shadow
133           Secure user account information.
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135       /etc/login.defs
136           Shadow password suite configuration.
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