vacation: 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 Debian possible default full paths are:

/usr/bin/vacation - from package: vacation

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

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