gtkwave: 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/gtkwave - from package: gtkwave

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

On Debian possible default full paths are:

/usr/bin/gtkwave - from package: gtkwave

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

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