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MAN page from OpenSuSE shadow-4.6-lp151.2.3.2.x86_64.rpm

CHPASSWD

Section: System Management Commands (8)
Updated: 04/29/2018
Index 

NAME

chpasswd - update passwords in batch mode 

SYNOPSIS

chpasswd [options]
 

DESCRIPTION

Thechpasswdcommand 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 bychpasswd. Also the password age will be updated, if present.

The default encryption algorithm can be defined for the system with theENCRYPT_METHODorMD5_CRYPT_ENABvariables of/etc/login.defs, and can be overwritten with the-e,-m, or-coptions.

chpasswdfirst 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 thechpasswdcommand 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-eoptions are specified), the encryption method is defined by theENCRYPT_METHODorMD5_CRYPT_ENABvariables 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 theCHROOT_DIRdirectory and use the configuration files from theCHROOT_DIRdirectory.

-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 theSHA_CRYPT_MIN_ROUNDSandSHA_CRYPT_MAX_ROUNDSvariables 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.defschange 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 theMD5_CRYPT_ENABvariable.

MD5_CRYPT_ENAB (boolean)

Indicate if passwords must be encrypted using the MD5-based algorithm. If set toyes, 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 tonoif you need to copy encrypted passwords to other systems which don't understand the new algorithm. Default isno.

This variable is superseded by theENCRYPT_METHODvariable or by any command line option used to configure the encryption algorithm.

This variable is deprecated. You should useENCRYPT_METHOD.

SHA_CRYPT_MIN_ROUNDS (number), SHA_CRYPT_MAX_ROUNDS (number)

WhenENCRYPT_METHODis set toSHA256orSHA512, 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 theSHA_CRYPT_MIN_ROUNDSorSHA_CRYPT_MAX_ROUNDSvalues is set, then this value will be used.

IfSHA_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).


 

Index

NAME
SYNOPSIS
DESCRIPTION
OPTIONS
CAVEATS
CONFIGURATION
FILES
SEE ALSO

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