tkaer: 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/tkaer - from package: aegis-tk

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

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