skill: 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/skill - from package: procps

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

On Debian possible default full paths are:

/usr/bin/skill - from package: procps

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

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