mysqldiskusage: 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/mysqldiskusage - from package: mysql-utilities

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

On Debian possible default full paths are:

/usr/bin/mysqldiskusage - from package: mysql-utilities

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

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