scsi-rescan: 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/scsi-rescan - from package: sg3_utils

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

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