chgpasswd: command not found

Have You tried accessing the binary with the full path?

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/usr/sbin/chgpasswd - from package: passwd

You may install the required package with command apt-get install {package}
Error in other languages:
chgpasswd: bevel nie gevind nie
chgpasswd: comandă negăsită
chgpasswd: comando não encontrado
chgpasswd: commande introuvable
chgpasswd: command not found
chgpasswd: käsku ei ole
chgpasswd: không tìm thấy lệnh
chgpasswd: komanda nerasta
chgpasswd: Kommando nicht gefunden.
chgpasswd: kommandot finns inte
chgpasswd: komut yok
chgpasswd: nie znaleziono polecenia
chgpasswd: níor aimsíodh an t-ordú
chgpasswd: no se encontró la orden
chgpasswd: no s'ha trobat l'ordre
chgpasswd: opdracht niet gevonden
chgpasswd: parancs nem található
chgpasswd: perintah tidak ditemukan
chgpasswd: príkaz nenájdený
chgpasswd: příkaz nenalezen
chgpasswd: команда не найдена
chgpasswd: командата не е открита
chgpasswd: 命令找不到
chgpasswd: コマンドが見つかりません