impressive: 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/impressive - from package: impressive

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

On Debian possible default full paths are:

/usr/bin/impressive - from package: impressive

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

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