sha3sum: 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/sha3sum - from package: sha3sum

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

On Debian possible default full paths are:

/usr/bin/sha3sum - from package: libdigest-sha3-perl

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

Error in other languages:
sha3sum: bevel nie gevind nie
sha3sum: comandă negăsită
sha3sum: comando não encontrado
sha3sum: commande introuvable
sha3sum: command not found
sha3sum: käsku ei ole
sha3sum: không tìm thấy lệnh
sha3sum: komanda nerasta
sha3sum: Kommando nicht gefunden.
sha3sum: kommandot finns inte
sha3sum: komut yok
sha3sum: nie znaleziono polecenia
sha3sum: níor aimsíodh an t-ordú
sha3sum: no se encontró la orden
sha3sum: no s'ha trobat l'ordre
sha3sum: opdracht niet gevonden
sha3sum: parancs nem található
sha3sum: perintah tidak ditemukan
sha3sum: príkaz nenájdený
sha3sum: příkaz nenalezen
sha3sum: команда не найдена
sha3sum: командата не е открита
sha3sum: 命令找不到
sha3sum: コマンドが見つかりません