chpasswd - update passwords in batch mode
man 查看帮助文档，输入：man chpasswd
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 overwitten 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 occured 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).
- chpasswd 是一个批量更新用户口令的命令
- chpasswd 会从标准输入批量读取成对的用户名和密码，并使用这些信息来更新现有的一组
用户 - 从标准输入读取的每行数据格式应为 username:password 即用户名和密码用冒号分隔开
- 默认情况下所提供的密码必须是明文，并通过chpasswd进行加密
- chpasswd 首先在内存中更新密码，在没有任何错误的情况下才会将更改的密码更新到磁盘中
- chpasswd 的应用场景主要是在一个比较大的系统环境下，同一时间创建了多个用户的情况
- 默认的加密算法可以通过修改/etc/login.defs中ENCRYPT_METHOD变量的值（默认值SHA512），可以通过-e,-m，-c选项覆盖默认的加密算法
常用选项如下：
-c 使用指定的方法来加密密码，可用的方法是DES、MD5、NONE、SHA512（前提是你的系统支持这些加密算法）
-e 输入的密码是加密后的密码
-m 当提供的密码没有加密时，使用MD5代替DES加密
-s 使用指定的rounds数值加密密码（SHA加密算法）- 如果指定的数值为0将使用默认的rounds数值5000
- 数值的范围在1000到999999999之间
- 可以使用-s参数跟上SHA256或SHA512
- 默认的最小和最大rounds定义在/etc/login.defs文件的SHA_CRYPT_MIN_ROUNDS和SHA_CRYPT_MAX_ROUNDS变量中
配置说明：下面列出的所有配置项都可以通过修改/etc/login.defs中的配置来生效
ENCRYPT_METHOD 该值定义了chpasswd默认的加密算法，该变量的值可以定义为：DES(默认)、MD5、SHA256、SHA512
SHA_CRYPT_MIN_ROUNDS 当ENCRYPT_METHOD的值定义为SHA256或SHA512时，将使用该变量的值作为SHA加密算法的最小rounds值
SHA_CRYPT_MAX_ROUNDS 当ENCRYPT_METHOD的值定义为SHA256或SHA512时，将使用该变量的值作为SHA加密算法的最大rounds值基本使用：
[root@prenv ~]# useradd chtest
[root@prenv ~]# chpasswd
chtest:123456
[root@prenv ~]# echo "chtest:123456" > passwd.txt
[root@prenv ~]# chpasswd < passwd.txt