path: root/man/man8/chpasswd.8

'\" t
.\"     Title: chpasswd
.\"    Author: Julianne Frances Haugh
.\" Generator: DocBook XSL Stylesheets vsnapshot <http://docbook.sf.net/>
.\"      Date: 06/21/2024
.\"    Manual: System Management Commands
.\"    Source: shadow-utils 4.15.2
.\"  Language: English
.\"
.TH "CHPASSWD" "8" "06/21/2024" "shadow\-utils 4\&.15\&.2" "System Management Commands"
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.SH "NAME"
chpasswd \- update passwords in batch mode
.SH "SYNOPSIS"
.HP \w'\fBchpasswd\fR\ 'u
\fBchpasswd\fR [\fIoptions\fR]
.SH "DESCRIPTION"
.PP
The
\fBchpasswd\fR
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:
.PP
\fIuser_name\fR:\fIpassword\fR
.PP
By default the passwords must be supplied in clear\-text, and are encrypted by
\fBchpasswd\fR\&. Also the password age will be updated, if present\&.
.PP
The default encryption algorithm can be defined for the system with the
\fBENCRYPT_METHOD\fR
or
\fBMD5_CRYPT_ENAB\fR
variables of
/etc/login\&.defs, and can be overwritten with the
\fB\-e\fR,
\fB\-m\fR, or
\fB\-c\fR
options\&.
.PP
\fBchpasswd\fR
first updates all the passwords in memory, and then commits all the changes to disk if no errors occurred for any user\&.
.PP
This command is intended to be used in a large system environment where many accounts are created at a single time\&.
.SH "OPTIONS"
.PP
The options which apply to the
\fBchpasswd\fR
command are:
.PP
\fB\-c\fR, \fB\-\-crypt\-method\fR\ \&\fIMETHOD\fR
.RS 4
Use the specified method to encrypt the passwords\&.
.sp
The available methods are
\fIDES\fR,
\fIMD5\fR, \fISHA256\fR, \fISHA512\fR
and
\fINONE\fR
if your libc supports these methods\&.
.sp
By default (if none of the
\fB\-c\fR,
\fB\-m\fR, or
\fB\-e\fR
options are specified), the encryption method is defined by the
\fBENCRYPT_METHOD\fR
or
\fBMD5_CRYPT_ENAB\fR
variables of
/etc/login\&.defs\&.
.RE
.PP
\fB\-e\fR, \fB\-\-encrypted\fR
.RS 4
Supplied passwords are in encrypted form\&.
.RE
.PP
\fB\-h\fR, \fB\-\-help\fR
.RS 4
Display help message and exit\&.
.RE
.PP
\fB\-m\fR, \fB\-\-md5\fR
.RS 4
Use MD5 encryption instead of DES when the supplied passwords are not encrypted\&.
.RE
.PP
\fB\-R\fR, \fB\-\-root\fR\ \&\fICHROOT_DIR\fR
.RS 4
Apply changes in the
\fICHROOT_DIR\fR
directory and use the configuration files from the
\fICHROOT_DIR\fR
directory\&. Only absolute paths are supported\&.
.RE
.PP
\fB\-P\fR, \fB\-\-prefix\fR\ \&\fIPREFIX_DIR\fR
.RS 4
Apply changes to configuration files under the root filesystem found under the directory
\fIPREFIX_DIR\fR\&. 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\&.
.RE
.PP
\fB\-s\fR, \fB\-\-sha\-rounds\fR\ \&\fIROUNDS\fR
.RS 4
Use the specified number of rounds to encrypt the passwords\&.
.sp
You can only use this option with crypt method:
\fISHA256\fR \fISHA512\fR
.sp
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\&.
.sp
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\&.
.RE
.SH "CAVEATS"
.PP
Remember to set permissions or umask to prevent readability of unencrypted files by other users\&.
.SH "CONFIGURATION"
.PP
The following configuration variables in
/etc/login\&.defs
change the behavior of this tool:
.PP
\fBENCRYPT_METHOD\fR (string)
.RS 4
This defines the system default encryption algorithm for encrypting passwords (if no algorithm are specified on the command line)\&.
.sp
It can take one of these values:
\fIDES\fR
(default),
\fIMD5\fR, \fISHA256\fR, \fISHA512\fR\&. MD5 and DES should not be used for new hashes, see
crypt(5)
for recommendations\&.
.sp
Note: this parameter overrides the
\fBMD5_CRYPT_ENAB\fR
variable\&.
.RE
.PP
\fBMD5_CRYPT_ENAB\fR (boolean)
.RS 4
Indicate if passwords must be encrypted using the MD5\-based algorithm\&. If set to
\fIyes\fR, 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
\fIno\fR
if you need to copy encrypted passwords to other systems which don\*(Aqt understand the new algorithm\&. Default is
\fIno\fR\&.
.sp
This variable is superseded by the
\fBENCRYPT_METHOD\fR
variable or by any command line option used to configure the encryption algorithm\&.
.sp
This variable is deprecated\&. You should use
\fBENCRYPT_METHOD\fR\&.
.RE
.PP
\fBSHA_CRYPT_MIN_ROUNDS\fR (number), \fBSHA_CRYPT_MAX_ROUNDS\fR (number)
.RS 4
When
\fBENCRYPT_METHOD\fR
is set to
\fISHA256\fR
or
\fISHA512\fR, 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)\&.
.sp
With a lot of rounds, it is more difficult to brute force the password\&. But note also that more CPU resources will be needed to authenticate users\&.
.sp
If not specified, the libc will choose the default number of rounds (5000), which is orders of magnitude too low for modern hardware\&.
.sp
The values must be inside the 1000\-999,999,999 range\&.
.sp
If only one of the
\fBSHA_CRYPT_MIN_ROUNDS\fR
or
\fBSHA_CRYPT_MAX_ROUNDS\fR
values is set, then this value will be used\&.
.sp
If
\fBSHA_CRYPT_MIN_ROUNDS\fR
>
\fBSHA_CRYPT_MAX_ROUNDS\fR, the highest value will be used\&.
.RE
.SH "FILES"
.PP
/etc/passwd
.RS 4
User account information\&.
.RE
.PP
/etc/shadow
.RS 4
Secure user account information\&.
.RE
.PP
/etc/login\&.defs
.RS 4
Shadow password suite configuration\&.
.RE
.SH "SEE ALSO"
.PP
\fBpasswd\fR(1),
\fBnewusers\fR(8),
\fBlogin.defs\fR(5),
\fBuseradd\fR(8)\&.