I read description of these command from a book,
passwd:
Changes the password for an existing user.
chpasswd:
Reads a file of login name and password pairs, and updates the passwords.
It seems these command doing same jobs. Is there a difference between them?
EDIT:
I want to learn when we use them which file(s) change. Do they change same file or different file? If they change different file(s), what are they?
From man chpasswd:
'This command is intended to be used in a large system environment where many accounts are created at a single time.'
passwd is (in my experience) normally used interactively for a single user.
In a nutshell:
passwd checks if the STDIN (file descriptor 0) is attached to the terminal, using isatty(0). If not, passwd would bail out i.e. you can only work with passwd interactively
chpasswd, on the other hand, is designed to read (username and) password from STDIN, and is called the batch mode (creates/updates multiple user credentials at once). It reads password(s) (in clear text by default), and username(s) from STDIN, given in the format user_name:password, with newline separating the entries
See man pages for both of them:
NAME
chpasswd - update passwords in batch mode
SYNOPSIS
chpasswd[options]DESCRIPTION
The
chpasswdcommand 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
NAME
passwd - change user password
SYNOPSIS
passwd[options] [LOGIN]DESCRIPTION
The
passwdcommand changes passwords for user accounts. A normal user may only change the password for his/her own account, while the superuser may change the password for any account.passwdalso changes the account or associated password validity period.
I found that although
echo user:password | chpasswd works for some OSes, some such as debian9,10 will show an error can not connect to /var/run/nscd/socket since it uses /etc/nsswitch.conf to determine where it stores the password.
On the other side, the passwd command seems does not need interactive shell,
(echo user; echo password) | passwd works for me both in physical host and container, for various OSes (ubuntu xenial-bionic, debian9-10, centos75-76, coreos1855-2135)
/etc/passwordcontains user account information./etc/shadowcontains encrypted passwords. I believe those are the only files that are relevant. You could change a password by manually editing those files, but it would be very awkward.