mkmanifest: 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/mkmanifest - from package: mtools

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

On Debian possible default full paths are:

/usr/bin/mkmanifest - from package: mtools

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

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