gnokii: 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/gnokii - from package: gnokii

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

On Debian possible default full paths are:

/usr/bin/gnokii - from package: gnokii-cli

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

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