huschi.net

CHPASSWD(8)               System Management Commands               CHPASSWD(8)

NAME
       chpasswd - update passwords in batch mode
SYNOPSIS
       chpasswd [options]
DESCRIPTION
       The chpasswd command reads a list of user name and password pairs from
       standard input and uses this information to update a group of existing
       users. Each line is of the format:
       user_name:password
       By default the passwords must be supplied in clear-text, and are
       encrypted by chpasswd. Also the password age will be updated, if
       present.
       The default encryption algorithm can be defined for the system with the
       ENCRYPT_METHOD or MD5_CRYPT_ENAB variables of /etc/login.defs, and can
       be overwritten with the -e, -m, or -c options.
       chpasswd first updates all the passwords in memory, and then commits
       all the changes to disk if no errors occurred for any user.
       This command is intended to be used in a large system environment where
       many accounts are created at a single time.
OPTIONS
       The options which apply to the chpasswd command are:
       -c, --crypt-method METHOD
           Use the specified method to encrypt the passwords.
           The available methods are DES, MD5, NONE, and SHA256 or SHA512 if
           your libc support these methods.
           By default (if none of the -c, -m, or -e options are specified),
           the encryption method is defined by the ENCRYPT_METHOD or
           MD5_CRYPT_ENAB variables of /etc/login.defs.
       -e, --encrypted
           Supplied passwords are in encrypted form.
       -h, --help
           Display help message and exit.
       -m, --md5
           Use MD5 encryption instead of DES when the supplied passwords are
           not encrypted.
       -R, --root CHROOT_DIR
           Apply changes in the CHROOT_DIR directory and use the configuration
           files from the CHROOT_DIR directory.
       -s, --sha-rounds ROUNDS
           Use the specified number of rounds to encrypt the passwords.
           The value 0 means that the system will choose the default number of
           rounds for the crypt method (5000).
           A minimal value of 1000 and a maximal value of 999,999,999 will be
           enforced.
           You can only use this option with the SHA256 or SHA512 crypt
           method.
           By default, the number of rounds is defined by the
           SHA_CRYPT_MIN_ROUNDS and SHA_CRYPT_MAX_ROUNDS variables in
           /etc/login.defs.
CAVEATS
       Remember to set permissions or umask to prevent readability of
       unencrypted files by other users.
CONFIGURATION
       The following configuration variables in /etc/login.defs change the
       behavior of this tool:
       ENCRYPT_METHOD (string)
           This defines the system default encryption algorithm for encrypting
           passwords (if no algorithm are specified on the command line).
           It can take one of these values: DES (default), MD5, SHA256,
           SHA512.
           Note: this parameter overrides the MD5_CRYPT_ENAB variable.
       MD5_CRYPT_ENAB (boolean)
           Indicate if passwords must be encrypted using the MD5-based
           algorithm. If set to yes, new passwords will be encrypted using the
           MD5-based algorithm compatible with the one used by recent releases
           of FreeBSD. It supports passwords of unlimited length and longer
           salt strings. Set to no if you need to copy encrypted passwords to
           other systems which don't understand the new algorithm. Default is
           no.
           This variable is superseded by the ENCRYPT_METHOD variable or by
           any command line option used to configure the encryption algorithm.
           This variable is deprecated. You should use ENCRYPT_METHOD.
       SHA_CRYPT_MIN_ROUNDS (number), SHA_CRYPT_MAX_ROUNDS (number)
           When ENCRYPT_METHOD is set to SHA256 or SHA512, this defines the
           number of SHA rounds used by the encryption algorithm by default
           (when the number of rounds is not specified on the command line).
           With a lot of rounds, it is more difficult to brute forcing the
           password. But note also that more CPU resources will be needed to
           authenticate users.
           If not specified, the libc will choose the default number of rounds
           (5000).
           The values must be inside the 1000-999,999,999 range.
           If only one of the SHA_CRYPT_MIN_ROUNDS or SHA_CRYPT_MAX_ROUNDS
           values is set, then this value will be used.
           If SHA_CRYPT_MIN_ROUNDS > SHA_CRYPT_MAX_ROUNDS, the highest value
           will be used.
FILES
       /etc/passwd
           User account information.
       /etc/shadow
           Secure user account information.
       /etc/login.defs
           Shadow password suite configuration.
SEE ALSO
       passwd(1), newusers(8), login.defs(5),useradd(8).

shadow-utils 4.6                  08/09/2019                       CHPASSWD(8)