iverilog-vpi: 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/iverilog-vpi - from package: iverilog

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

On Debian possible default full paths are:

/usr/bin/iverilog-vpi - from package: iverilog

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

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