since: 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/since - from package: since

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

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