isosize: 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/isosize - from package: util-linux-ng

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

On Debian possible default full paths are:

/sbin/isosize - from package: util-linux

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

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