sha384sum: 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/sha384sum - from package: coreutils

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

On Debian possible default full paths are:

/usr/bin/sha384sum - from package: coreutils

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

Error in other languages:
sha384sum: bevel nie gevind nie
sha384sum: comandă negăsită
sha384sum: comando não encontrado
sha384sum: commande introuvable
sha384sum: command not found
sha384sum: käsku ei ole
sha384sum: không tìm thấy lệnh
sha384sum: komanda nerasta
sha384sum: Kommando nicht gefunden.
sha384sum: kommandot finns inte
sha384sum: komut yok
sha384sum: nie znaleziono polecenia
sha384sum: níor aimsíodh an t-ordú
sha384sum: no se encontró la orden
sha384sum: no s'ha trobat l'ordre
sha384sum: opdracht niet gevonden
sha384sum: parancs nem található
sha384sum: perintah tidak ditemukan
sha384sum: príkaz nenájdený
sha384sum: příkaz nenalezen
sha384sum: команда не найдена
sha384sum: командата не е открита
sha384sum: 命令找不到
sha384sum: コマンドが見つかりません