scsi_readcap: 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 Debian possible default full paths are:

/usr/bin/scsi_readcap - from package: sg3-utils

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

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