ip: 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:

/sbin/ip - from package: iproute

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

On Debian possible default full paths are:

/sbin/ip - from package: iproute2
/bin/ip - from package: iproute2

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

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