sip: 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/sip - from package: sip-devel

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

On Debian possible default full paths are:

/usr/bin/sip - from package: sip-dev

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

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