NetworkManager: 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/sbin/NetworkManager - from package: NetworkManager

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

On Debian possible default full paths are:

/usr/sbin/NetworkManager - from package: network-manager

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

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