nmap: 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/nmap - from package: nmap

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

On Debian possible default full paths are:

/usr/bin/nmap - from package: nmap

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

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