]> Julianne Frances Haugh Creation, 1991 Thomas Kłoczko kloczek@pld.org.pl shadow-utils maintainer, 2000 - 2007 Nicolas François nicolas.francois@centraliens.net shadow-utils maintainer, 2007 - now chpasswd 8 System Management Commands shadow-utils &SHADOW_UTILS_VERSION; chpasswd update passwords in batch mode chpasswd options 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. By default, passwords are encrypted by PAM, but (even if not recommended) you can select a different encryption method with the -e, -m, or -c options. Except when PAM is used to encrypt the passwords, chpasswd first updates all the passwords in memory, and then commits all the changes to disk if no errors occurred for any user. When PAM is used to encrypt the passwords (and update the passwords in the system database) then if a password cannot be updated chpasswd continues updating the passwords of the next users, and will return an error code on exit. This command is intended to be used in a large system environment where many accounts are created at a single time. 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 BCRYPT, DES, MD5, SHA256, SHA512, YESCRYPT and NONE if your libc supports these methods. By default, PAM is used to encrypt the passwords. 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. Only absolute paths are supported. -P, --prefix PREFIX_DIR Apply changes to configuration files under the root filesystem found under the directory PREFIX_DIR. This option does not chroot and is intended for preparing a cross-compilation target. Some limitations: NIS and LDAP users/groups are not verified. PAM authentication is using the host files. No SELINUX support. -s, --sha-rounds ROUNDS Use the specified number of rounds to encrypt the passwords. You can only use this option with crypt method: BCRYPT SHA256 SHA512 YESCRYPT By default, the number of rounds for BCRYPT is defined by the BCRYPT_MIN_ROUNDS and BCRYPT_MAX_ROUNDS variables in /etc/login.defs. A minimal value of 4 and a maximal value of 31 will be enforced for BCRYPT. The default number of rounds is 13. By default, the number of rounds for SHA256 or SHA512 is defined by the SHA_CRYPT_MIN_ROUNDS and SHA_CRYPT_MAX_ROUNDS variables in /etc/login.defs. A minimal value of 1000 and a maximal value of 999,999,999 will be enforced for SHA256 and SHA512. The default number of rounds is 5000. By default, the number of rounds for YESCRYPT is defined by the YESCRYPT_COST_FACTOR in /etc/login.defs. A minimal value of 1 and a maximal value of 11 will be enforced for YESCRYPT. The default number of rounds is 5. Remember to set permissions or umask to prevent readability of unencrypted files by other users. The following configuration variables in /etc/login.defs change the behavior of this tool: &ENCRYPT_METHOD; &MD5_CRYPT_ENAB; &BCRYPT_MIN_ROUNDS; &SHA_CRYPT_MIN_ROUNDS; &YESCRYPT_COST_FACTOR; /etc/passwd User account information. /etc/shadow Secure user account information. /etc/login.defs Shadow password suite configuration. /etc/pam.d/chpasswd PAM configuration for chpasswd. passwd1 , newusers8 , login.defs5 , useradd8 .