passwd: command not found

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 CentOS possible default full paths are:

/usr/bin/passwd - from package: passwd

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/passwd - from package: passwd

You may install the required package with command apt-get install {package}

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