iverilog: 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 - from package: iverilog

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

On Debian possible default full paths are:

/usr/bin/iverilog - from package: iverilog

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

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