sak: 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/sak - from package: seqan-apps
/usr/lib/seqan/bin/sak - from package: seqan-apps

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

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