multipathd: 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:

/sbin/multipathd - from package: device-mapper-multipath

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

On Debian possible default full paths are:

/sbin/multipathd - from package: multipath-tools
/usr/lib/debug/sbin/multipathd - from package: multipath-tools-dbg

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

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