sipsak: 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/sipsak - from package: sipsak

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

On Debian possible default full paths are:

/usr/bin/sipsak - from package: sipsak

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

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